sa 1... science .. class 10

Study material (Science) (Class 10)

Notes Assembled by Anupam Narang (8802442964)([email protected])

Electricity

Electricity is used in our homes, in industry and in transport.

Example: - In homes lightening, operating fans and for heating purpose.

In industry used in running machines.

In transport used in electric trains, street lightning, etc

Types of electric charges

There are two types of electric charges: positive charges and negative charges.

The charge acquired by glass rod is positive charge and charge acquired by silk

cloth is negative charge, when glass rod is rubbed with the silk cloth. The charge

acquired by ebonite rod is negative charge and charge acquired by wool is positive

charge, when ebonite rod is rubbed with the wool.

Property of electric charges

1. Opposite charges or unlike charges attract each other. (a positive charge

attract negative charge)

2. Similar charges or like charges repel each other. (two positive charges or two

negative charges repel each other)

The SI unit of electric charge is “coulomb (C)”.

One coulomb is the quantity of electric charge which exerts a force of 9 × 109

Newton on an equal charge placed at a distance of 1m from it.

All matters contain positively charged particles called protons and negatively

charged particles called electrons. A proton carries a positive charge of 1.6 × 10-19 C

and electron carries a negative charge of 1.6 × 10-19.

The unit of electric charge is much bigger than the charge of proton or electron.

Conductors and insulators

All the substances can be categorized in two electric categories: - conductors and

insulators.

The substances through which charges can flow easily are called conductors.

The conductors can also be defined as the substances through which electricity can

flow easily. Example: - all metals (silver, aluminium, etc), metal alloys (manganin,

constantan), carbon in the form of graphite and human body.

Those substances through electric charges can not flow are called insulators.

Insulators can also be defined as the substances through which electricity does not

flow. Example: - plastic, glass, ebonite, etc.

In case of glass rod rubbed with silk and ebonite rod rubbed with wool, the charges

attained by glass rod and ebonite rod are fixed but they don‟t move.

All the conductors have some free electrons which are loosely held by the nucleus

of their atoms. These free electrons can move from one atom to another throughout

conductor. The presence of these free electrons in the substance makes it a

conductor.

Electricity



The electrons present in the insulators are tightly bound by the nucleus of the

atoms of insulators due to which they can not move from one atom to another, this

property makes a substance insulator.

Types of electricity

Electricity can be divided in two parts on the bases of the movement of charges.

1. Static electricity:-

The type of electricity in which charges are at rest or do not move is called static

electricity. Example:- the charges acquired by glass rod and silk cloth, when

they are rubbed with each other, the charges acquired by the ebonite rod and

wool, when they are rubbed with each other and lightening in the sky.

2. Current electricity:-

The type of electricity in which charges are in motion is called current electricity.

Example: - the electricity we use in our homes.

Electric potential

The electric potential at any point in the electric field is defined as the work done

in moving a unit positive charge from infinity to that point.

Electric potential is denoted by “V” and its SI unit is “volt”.

When 1 joule of work is done to move 1 C of positive charge form infinity to a point

then the electric potential at that point is said to be 1 volt or 1 V.

Potential difference

The difference in the electric potential between two points is called potential

difference.

The potential difference between the two points in an electric circuit is defined as

amount of work done in moving a unit positive charge from one point to another

point is called potential difference between the two points.

Potential difference (p.d) = 𝑤𝑜𝑟𝑘 𝑑𝑜𝑛𝑒

𝑞𝑢𝑎𝑛𝑡𝑖𝑡𝑦 𝑜𝑓 𝑐𝑕𝑎𝑟𝑔𝑒 𝑚𝑜𝑣𝑒𝑑

V = 𝑊

𝑄

The SI unit of potential difference is “volt (V)”.

The potential difference between the two points is said to be 1 volt if 1 joule of work

is done to move 1 coulomb of positive charge form one point to another point.

1 volt = 1 𝐽

1 𝐶 1 V = 1 J/C = 1 JC-1

Electric current

When two bodies kept at different electric potentials are connected by a metal wire

then the electric charges flow from body at high potential to the body at low

potential through the wire till both the bodies are at same potential.

It is the potential difference between the two bodies which makes the electric

charges to flow in the wire.

The electric charges which flow in the wire are electrons.

The electric current can be defined as the flow of electrons in the conductor such

as metal wire.



The magnitude of the electric current in a conductor is the amount of electric

charge passing through a given point of the conductor in one second.

Current (I) = 𝑄

𝑡 , where “Q” is the charge in coulomb and “t” is the time taken in

seconds.

The SI unit of electric current is ampere (A).

When 1 C of charge is flows through any cross section of a conductor in 1 second,

then the electric current flowing through the wire is said to be 1 ampere (1 A).

1 A = 1 𝐶

1 𝑠𝑒𝑐𝑜𝑛𝑑 = 1 C /s = 1 C s-1

1 milliampere = 1

1000 ampere 1 mA = 10-3 A

Measurement of potential difference

The potential difference is measured by an instrument called voltmeter.

The voltmeter is always connected in parallel across the two points where the

potential difference is to be measured.

A voltmeter has a high resistance so that it takes negligible current from the

circuit.

Voltage is another name of potential difference.

Measurement of electric current

Current is measured by an instrument called ammeter.

The ammeter is always connected in series with the circuit with which the current

is to be measured.

To measure the current in the circuit, the entire current is to be passed through

the ammeter, therefore the ammeter should have very low resistance so that it may

not change the value of the current flowing in the circuit.

How to get the continuous flow of electric current?

The simplest way to maintain the potential difference

between the two ends of the conductor so as to get the

continuous flow electric current is to connect the

conductor with in the two terminals of the battery or

cell.

Direction of electric current

In the past electricity was discovered prior to

the electrons. Therefore, the electric current or

electricity was considered to be the flow of

positive charges and the direction of flow

electric charges was taken as the direction of

electric current.

The conventional direction of electric current is

from the positive terminal to the negative

terminal through the outer circuit.



Later when the electrons were

discovered, it was found that the

positive charges can not flow through a

metal conductor. Therefore, the electric

current through a metal conductor was

defined as the flow of electrons.

The electrons flow from negative

terminal to positive terminal in the

outer circuit. But the direction of

electric current is from the positive terminal to negative terminal.

How the electric current flows in the

wire?

When the metal wire has not been

connected to a source like cell or

battery, then the electrons present in it

move at random in all directions

between the atoms of the metal wire.

When a source of energy like cell or

battery is connected between the ends

of the metal wire, then an electric force acts on the electrons present in the wire.

Since the electrons are negatively charged, they start moving from negative

terminal to positive terminal of the wire.

Electric circuits

A continuous conducting path consisting of wires and

other resistances and switch, between the two terminals

of the cell or a battery along which an electric current

flows, is called a circuit.

Symbols of electric components (or circuit symbols)

Components Symbols

An electric cell

Connecting wire

An electric battery or a

combination of cells

Plug key or switch (open)

or



Plug key or switch (close)

or

A wire joint

Wires crossing without joining

Electric bulb

A resistor of resistance R

Variable resistance or rheostat

Ammeter

Voltmeter

Galvanometer

Circuit diagrams

A diagram which show that how different components are connected by using the

electric symbols for the components called circuit diagram.

G

A circuit diagram consisting of a

cell, a bulb and a closed switch.

A circuit diagram consisting of a

cell, a bulb and an open switch.

Voltmeter connected

parallel with the resistor.



Ohm’s law

According to ohm‟s law, at constant temperature, the current flowing through a

conductor is directly proportional to the potential difference across its ends.

If I is the current flowing through a conductor and V is the potential difference

across its ends, then according to ohm‟s law:

I V (at constant temperature)

This can also be written as : V I

V = R × I

Where “R” is the constant called resistance of the conductor.

R = 𝑉

𝐼 (V = potential difference, I = current and R = resistance)

The ratio of the potential difference applied between the ends of a conductor to the

current flowing through it is a constant quantity called resistance.

R = 𝑉

𝐼 current, I =

𝑉

𝑅

Factors affecting the strength of electric current:

i. Potential difference across the ends of the conductor.

ii. Resistance of the conductor.

Resistance of the conductor

When the electrons move from one part to another part, they collide with other

electrons and with the atoms and ions present in the body of the conductor.

The property of a conductor due to which it opposes the flow of current is called

resistance.

Resistance = 𝑝𝑜𝑡𝑒𝑛𝑡𝑖𝑎𝑙 𝑑𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒

𝑐𝑢𝑟𝑟𝑒𝑛𝑡 R =

𝑉

𝐼

Ammeter in series with the circuit.

resistor

Connecting wire cell switch



The SI unit of the resistance is “ohm (represented by symbol omega “”)”.

1 ohm is the resistance of the conductor such that when a potential difference of I

volt is applied across its ends, and a current of 1 ampere flows through it.

1 = 1 𝑉

1 𝐴

Graph between V and I

current (I) potential difference (V)

the graph between V and I is straight line passing through origin

Good conductors and insulators

Those substances which have low electrical resistance are called good conductors.

Good conductors allow the passage of electric current easily. Silver is the best

conductor. Copper and aluminium are good conductors. Electric wires are made of

Cu and Al because they have low electric resistance.

Those substances which have comparatively high electric resistance are called

resistors. Example: nichrome, manganin and constantan. Resistors reduces the

current in wire.

Those substances which have infinitely high electric resistance are called

insulators. They do not allow the electric current to flow. Example: rubber, glass,

etc

Factors affecting the resistance of conductor

i. Length of conductor

ii. Area of cross-section of conductor or thickness of conductor

iii. Nature of the material of the conductor

iv. Temperature of conductor

Effect of length of conductor

The resistance of the conductor is directly proportional to its length.

Resistance length of conductor R l

When length of conductor is doubled its resistance also gets doubled and if the

length of conductor is halved then its resistance also gets halved.

Effect of Area of cross-section of conductor or thickness of conductor

The resistance of the conductor is inversely proportional to its Area of cross-section

or thickness of conductor.



Resistance 1

Area of cro ss−section of conductor or thickness of conductor R

1

𝐴

When Area of cross-section of conductor is doubled its resistance gets halved and if

the Area of cross-section of conductor is halved then its resistance gets doubled.

Resistance of the conductor is also inversely proportional to the square of the

radius of wire and also inversely proportional to the square of the diameter of wire.

If radius or diameter of wire is doubled then the resistance of the wire gets one-

fourth.

Resistance 1

radius of wire 2 R 1

𝑟2

Resistance 1

diameter of wire 2 R 1

𝑑2

Effect of Nature of the material of the conductor

Resistance of the conductor depends on the type of material of which it is made.

Some materials like metals have low resistance but some materials like nichrome

have high resistance.

Resistance of nichrome wire is 60 times more than the copper wire of same length

and same cross-section area.

Effect of temperature

The resistance of all pure metals increases on raising the temperature and

decreases on decreasing the temperature.

Resistance of alloys like manganin, nichrome and constantan is almost unaffected

by temperature.

Resistance of semiconductor materials like silicon and germanium decreases on

increasing the temperature.

Resistivity

The resistance of the conductor is directly proportional to its length.

Resistance length of conductor R l ………………. (1)

The resistance of the conductor is inversely proportional to its Area of cross-section

or thickness of conductor.

Resistance 1

Area of cross −section of conductor or thickness of conductor R

1

𝐴 … (2)

Combining (1) and (2), we get

R 𝑙

𝐴

R = 𝑙

𝐴

[ (Rho) is a constant known as resistivity of the material of the conductor.]

Resistance of the material is directly proportional to the resistivity of the conductor.

If we change the material of the conductor to one whose resistivity is two times

then the resistance of the conductor also becomes two times, and vice versa.

Resistance resistivity R

The mathematical reaction for the resistivity of the conductor:-

= R 𝐴

𝑙



(R = resistance of conductor, l = length of conductor and A = area of cross-section of

conductor)

The resistivity of the substance is numerically equal to the resistance if the rod of

that substance which is 1 meter long and 1 meter in cross-section. Resistivity of a

substance is equal to the resistance between the opposite faces of a 1 meter cube of

the substance.

SI unit of resistivity:- = R 𝐴

𝑙 =

𝑜𝑕𝑚 × 𝑚𝑒𝑡𝑟𝑒 2

𝑚𝑒𝑡𝑟𝑒 = ohm – metre

Factors affecting the resistivity of the substance

Resistivity of the substance depends on the temperature of substance and nature

of substance. It does not depend on the length and area of cross-section of

substance.

Silver is the best conductor of electricity. But it can not be used to make electrical

wires because it is very costly. Copper and aluminium are used to make electrical

wires because these metals are also having low resistivity and they are not much

costly.

The heating elements of the heating appliances

such as iron and toasters are made of an alloy

rather than pure metal. Because:- the

resistivity of the alloy is much higher than that

of pure metal due to which the heating element

produces lot of heat on passing the electric

current, an alloy do not burn easily or does not

undergoes oxidation at high temperatures,

when it is red hot. Heating elements of the

heating appliances are made of nichrome alloy.

The resistivity of insulators like ebonite, glass and diamond is very high and do not

change with temperature.

The resistivity of semiconductors like silicon and germanium is in between those of

conductors and insulators and decreases on increasing temperature.

Combination of resistances or resistors

The resistances can be combined in two ways:- (1) In series (2) in parallel

When two or more resistances are connected end to end consecutively, they are

said to be connected in series.

When two or more resistances are connected between the same two points, they are

said to be connected in parallel.

Resistances or resistors in series

The combined resistance of any number of resistances connected in series is equal

to the sum of the individual resistances.

R = R1 + R2

When a number of resistances are connected in series, then:-



i. Each resistance has a different potential difference across its ends. The sum of

potential differences across all the resistances is equal to the voltage of the

battery applied.

ii. When a number of resistances are

connected in series then same current

flows through them.

Resultant resistances of two resistances

are connected in series

Two resistances R1 and R2 connected in

series. A battery of V volts has been applied

to the ends of the series combination. V1 is

the potential difference across R1 and V2 is

the potential difference across R2.

For the series combination of resistances the

sum of Potential differences across all resistors is equal to the voltage of battery.

V = V1 + V2 ………….(1)

If I is the current flowing in the circuit,

Then by ohm‟s law, V = I × R ………….(2)

Since same current passes through each resistor,

By ohm‟s law V1 = I × R1

………….(3) and V2 = I × R2 ………….(4)

Using (1), (2), (3) and (4)

I × R = I × R1 + I × R2

I × R = I × (R1 + R2)

R = R1 +R2

Resultant resistances of three

resistances are connected in series

Three resistances R1, R2 and R3 connected

in series. A battery of V volts has been

applied to the ends of the series

combination. V1 is the potential difference

across R1, V2 is the potential difference

across R2 and V3 is the potential

difference across R3.

For the series combination of resistances the sum of Potential differences across all

resistors is equal to the voltage of battery.

V = V1 + V2 + V3 …………. (1)

If I is the current flowing in the circuit,

Then by ohm‟s law, V = I × R …………. (2)

Since same current passes through each resistor,

By ohm‟s law V1 = I × R1 ….(3) ,

V2 = I × R2 ……(4) and V3 = I × R3 ….(5)

Using (1), (2), (3), (4) and (5)



I × R = I × R1 + I × R2 + I × R3

I × R = I × (R1 + R2+ R3)

R = R1 +R2+ R3

Resistances or resistors in parallel

The combined resistance of any number of resistances connected in parallel is

equal to the sum of reciprocals of all the

individual resistances. 1

𝑅 =

1

𝑅1 +

1

𝑅2

When a number of resistances are connected

in parallel, then:-

i. Each resistance has same potential

difference across its ends, which is equal

to the potential difference of the battery.

ii. When a number of resistances are

connected in parallel then different

amount of current flows through each resistance. The sum of currents through

all the resistors is equal to the total current drawn from the battery.

Resultant resistances of two resistances are connected in parallel

Two resistances R1 and R2 connected in parallel. A battery of V volts has been applied

to the ends of the parallel combination. I1 is the current flowing through R1 and I2 is

the current flowing through R2.

For the parallel combination of resistances the sum of currents flowing through all

resistors is equal to the total current drawn from the battery.

I = I1 + I2 ………….(1)

If I is the total current flowing in the circuit, R is the total resistance of the parallel

combination of resistances and V is the potential difference of the battery applied.

Then by ohm‟s law, I = 𝑉

𝑅 ………….(2)

Since there is same potential difference across each resistor,

By ohm‟s law I1 = 𝑉

𝑅1 ………….(3) and I2 =

𝑉

𝑅2 ………….(4)

Using (1), (2), (3) and (4) 𝑉

𝑅 =

𝑉

𝑅1 +

𝑉

𝑅2

𝑉

𝑅 = V

1

𝑅1 +

1

𝑅2

1

𝑅 =

1

𝑅1 +

1

𝑅2

Resultant resistances of three resistances are connected in parallel

Three resistances R1, R2 and R3 connected in parallel.



A battery of V volts has been applied to the ends of the parallel combination. I1 is the

current flowing through R1, I2 is the current flowing through R2 and I3 is the current

flowing through R3.

For the parallel combination of resistances the sum of currents flowing through all

resistors is equal to the total current drawn from the battery.

I = I1 + I2 + I3 ………….(1)

If “I” is the total current flowing in the circuit, “R” is the total resistance of the parallel

combination of resistances and “V” is the potential difference of the battery applied.

Then by ohm‟s law, I = 𝑉

𝑅 ………….(2)

Since there is same potential difference across each resistor,

By ohm‟s law I1 = 𝑉

𝑅1 ………….(3) , I2 =

𝑉

𝑅2 ………….(4) and I3 =

𝑉

𝑅3

………….(5)

Using (1), (2), (3), (4) and (5) 𝑉

𝑅 =

𝑉

𝑅1 +

𝑉

𝑅2 +

𝑉

𝑅3

𝑉

𝑅 = V

1

𝑅1 +

1

𝑅2 +

1

𝑅3

1

𝑅 =

1

𝑅1 +

1

𝑅2 +

1

𝑅3

Domestic electric circuits (series or parallel)

Disadvantages of series circuit for domestic wiring

In series circuit if one electrical appliance stops working due to some defect, then

all appliances stop working because the whole circuit is broken.

Example:- in diwali lights the bulbs are connected in series, if one bulb gets fused

then all bulbs stop working.

In series circuit there is only one switch for all electrical appliances, due to which

they can not be turned on and off separately.

Example:- if all the appliances in our home are connected in series then we will not

be able to run them separately.

In series circuit all the electrical

appliances do not get the same voltage

(220 V) from the power supply line

because the voltage is shared by all the

appliances, due to which the appliance

getting low voltage do not work properly.

Example:- if some bulbs are connected in

series connection they will not get the

proper voltage and hence they will glow

less brightly.

In the series connection of electrical

appliances, the over all resistance of the

electrical circuit increases much due to

which the current from the power supply

is low.



Advantages of parallel circuits in domestic wiring

In parallel circuit if one electrical appliance stops working due to some defect, then

all appliances keep working normally.

Example:- if number of bulbs are connected in parallel and one bulb gets fused

then all bulbs keep working.

In parallel circuit each electrical appliance has its own switch due to which it can

be turned on and off independently, without affecting other appliances.

Example:- all the appliances in our home are connected in parallel due to which

each appliance can be turned on and off separately.

In parallel circuit all the electrical appliances get the same voltage (220 V) from the

power supply line because the voltage is not shared by all the appliances, due to

which all the appliances get proper voltage and work properly.

Example:- if some bulbs are connected in parallel connection then they will get the

proper voltage and hence they will glow equally bright.

In the parallel connection of electrical appliances, the over all resistance of the

electrical circuit is reduced very much due to which the current from the power

supply is high and each appliance draws the required amount of current for its

working.

Electric power

When an electric current flow through the conductor, electrical energy is used up

and electric work is done.

Electric power is defined as electric work done per unit time. “Or”. Rate of doing

electric work is also called power. “Or”. Rate at which electrical energy is consumed

by the appliance is called power.

Power = 𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐 𝑤𝑜𝑟𝑘 𝑑𝑜𝑛𝑒

𝑡𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛 P =

𝑊

𝑡

SI unit of electric power is “watt (W)”. Another unit of electric power is “joule /

second (J/s) or J s-1”.

The electric power is said to be 1 watt if 1 joule of electric work is done in 1 sec or 1

joule of electrical energy is consumed by appliance in 1 sec.

1 watt = 1 𝑗𝑜𝑢𝑙𝑒

1 𝑠𝑒𝑐𝑜𝑛𝑑

The bigger units of electric power used for commercial purpose are “kilowatt and

megawatt”.

1 kilowatt = 1000 watt and 1 megawatt = 106 watt

Formula for calculating electric power

We know that, power is defined as rate at which electric work is done

Power = 𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐 𝑤𝑜𝑟𝑘 𝑑𝑜𝑛𝑒

𝑡𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛 P =

𝑊

𝑡 ………… (1)

Potential difference between two points is defined as the amount of electric work done

in moving a unit amount of charge form one point to another point.

Potential difference (p.d) = 𝑤𝑜𝑟𝑘 𝑑𝑜𝑛𝑒

𝑞𝑢𝑎𝑛𝑡𝑖𝑡𝑦 𝑜𝑓 𝑐𝑕𝑎𝑟𝑔𝑒 𝑚𝑜𝑣𝑒𝑑 V =

𝑊

𝑄 W = V × Q ….. (2)

Electric current is defined as flow of electrons per unit time.



Electric current (I) = 𝑞𝑢𝑎𝑛𝑡𝑖𝑡𝑦 𝑜𝑓 𝑐𝑕𝑎𝑟𝑔𝑒 𝑚𝑜𝑣𝑒𝑑

𝑡𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛 I =

𝑄

𝑡 Q = I × t …….. (3)

Using (2) and (3)

W = V × I × t …………. (4)

Using (1) and (4)

P = V × I × t

𝑡 = V × I electric power = voltage × current

The power of an electrical appliance depends upon the potential difference between

the terminals of the appliance and current flowing through it.

If an electrical appliance is operated at a potential difference of 1 volt and the

appliance carries the current of 1 ampere, then the power of the appliance is 1

watt.

1 watt = 1 volt × 1 ampere 1 W = 1 V × 1 A

Some other formulae of calculating electric power

Power P in terms of I and R

P = V × I …………………… (1)

From ohm‟s law, R = 𝑉

𝐼 V = I × R ……. (2)

Using (1) and (2),

P = I × I × R

P = I2 × R

I = current, R = resistance

Power P in terms of V and R

P = V × I …………………… (1)

From ohm‟s law, R = 𝑉

𝐼 I =

𝑉

𝑅 ……. (2)

Using (1) and (2),

P = V × 𝑉

𝑅

P = 𝑉2

𝑅

V = potential difference, R = resistance

Power voltage rating of the electrical appliance

The power voltage rating of the electrical appliance tells us about the voltage

needed for the effective working of appliance and power used by it.

Electrical energy

Electrical energy of the appliance is defined as the work done by the electric

current to flow through the appliance.

Electrical energy of the appliance is given by the product of its power rating and the

time for which it is used.

Electrical energy = power × time E = P × t

The SI unit is “joule (J)”.



One joule of the electric energy is defined as the energy consumed by an appliance

of power 1 watt in 1 sec.

If we take the unit of power as “watt (W)” and the unit of the time as “hour (h)” then

the unit of the electrical appliance is “watt-hour (Wh)”.

One watt-hour of the electrical energy is defined as the amount of energy consumed

by an appliance of power 1 watt in 1 hour.

Factors on which electrical energy consumed by the appliance depends

1) Power rating of the appliance

2) Time for which the appliance is used

Commercial unit of electric energy: kilowatt-hour (kWh)

1 kilowatt-hour is the amount of electrical energy consumed by an appliance of

1kW in 1 hour.

1 kilowatt-hour is equal to 1 unit of electrical energy.

Relation between the kilowatt-hour and joule

Electrical energy = power × time E = P × t

1 kWh = 1 kW × 1 h

1 kWh = 1000 W × 3600 s

1 kWh = 3600000 Ws

1 kWh = 3600000 J …………………… (1 Ws = 1 J)

1 kWh = 3.6 × 106 J

Effects produced by electric current

Heating effects, magnetic effects and chemical effects.

Heating effect of electric current

When an electric current is passed through a high resistance wire, like nichrome

wire, the resistance wire becomes very hot and produces heat. This is called

heating effects of electric current.

Joule’s law of heating (formula of heat energy)

“R” is resistance of the conductor, “I” is the current flowing through it for time “t”.

When a current flows through the conductor then some work is done the current ato

overcome resistance. Electric charge “Q” moves against the potential difference “V”,

the amount of work done “W” is:

W = Q × V……………………. (1)

Current is defined as the rate of flow of charge.

Current = 𝑐𝑕𝑎𝑟𝑔𝑒

𝑡𝑖𝑚𝑒 I =

𝑄

𝑡 Q = I × t……………………. (2)

From the ohm‟s law, V = I × R ……………………… (3)

Using (1), (2) and (3)

W = (I × t) × (I × R) = I2 R t

Since the electric work done against the resistance is converted into heat energy.



W = H

H = I2 R t

Factors on which the heat produced in a wire depends

1) Square of current (I2):- heat produced in a wire is directly proportional to the

square of current. H I2

If we will double the current then the heat produced becomes four times. If the

current is halved then the heat becomes one-fourth.

2) Resistance of wire (R):- heat produced in a wire is directly proportional to the

resistance of wire. H R

If we will double the resistance then the heat produced becomes two times. If the

resistance is halved then the heat becomes half.

3) Time for which current is passed (t):- heat produced in a wire is directly

proportional to time for which current is passed. H t

If we will double the time then the heat produced becomes two times. If the time is

halved then the heat becomes half.

Applications of heating effect of electric current

The heating effect of current is used I the working of the electrical heating

appliances such as electric iron, electric kettle, Electric toaster, electric oven, room

heaters, water heaters, electric geysers, etc.

The heating effect of electric current is utilized in electric bulbs or electric lamps for

producing light.

The heating effect of electric current is utilized in electric fuse for protecting

household wiring and electrical appliances.

Why does the coil of the heating appliance get heated up to a high temperature

(900C) but the connecting wires of the appliances do not get heated up?

The resistance of the heating elements of the heating appliance is very high due to

which the amount of heat is very high due to the heating effect of electric current

but the resistance of the connecting wires of the appliance is very low due to which

no heat is produced in the connecting wires.

Why tungsten metal is used in making the filaments of electric bulb?

Tungsten has high melting point of 3380C due to which it can be kept white hot

without melting away.

Tungsten has high flexibility and low rate of evaporation at high temperature.

What is the temperature of the tungsten filament when it is white hot?

2500C

Which gases are present in the bulb? Why the gases are filled in the bulb?

Nitrogen or argon or mixture of both is filled in bulb. The gases like nitrogen and

argon are inert in nature so they do not react with tungsten metal and they also

help tungsten metal to dissipate heat in the surroundings keeping the temperature



of filament below the melting point (3380C). Due to this action of gases the life of

tungsten filament is prolonged.

What will happen if the tungsten metal is kept in air at high temperature?

It will burn up quickly reacting wit the oxygen present in the air.

Out of bulb and tube light, which is more power efficient and why?

Tubelight is more power efficient.

In bulb most of the electric power is used up in producing heat in the filament and

some amount of the electric power is converted into light so bulb is not power

efficient. Io tube light there is no filament due to which most of the power is

converted into light which makes the tubelight power efficient.

What is a fuse wire? How does it work?

Fuse wire is a short length of thin tin plated copper wire having low melting point

but high resistance than the total resistance of the house.

When the current in the household circuit exceeds too much due to some reason,

then fuse wire gets heated up, melts and breaks the circuit. Breaking of circuit

leads to stop the flow of large current in the appliances in our house and prevents

the damage to various electrical appliances.

Why the resistance of fuse wire is kept more than the resistance of the

household circuit?

Resistance of fuse wire is kept more than resistance of the house hold circuit so

that the required amount of the current flows into the household circuit without

any obstruction.

Assignment

I. VERY SHORT ANSWER QUESTIONS (1 MARK)

(Answer the questions in one word or one sentence)

1. Multiple choice questions:

i. The S.I. unit of resistivity is

(a) Ω (b) Ω/cm (c) Ω m (d) Ω/m

ii. One horse power is equal to the

(a) 736 W (b) 746 W (c) 700 W (d) 726 W

iii. The instruments used to measure electric potential difference is

(a) voltmeter (b) ammeter (c) rheostat (d) generator

iv. Which of the following is not the unit of energy?

(a) Joule (b) kWh (c) kWs (d) kW

v. Resistivity of a wire depends upon the

(a) length (b) shape (c) thickness (d) material of wire

vi. Which of the following term does not represent electrical power in a circuit?

(a) I2R (b) IR2 (c) VI (d) V2/R

vii. An electric bulb is rated 220 V and 100 W. when it is operated at 110 V, the power consumed will

be

(a) 100 W (b) 75 W (c) 50 W (d) 25 W

viii. The power of a bulb producing 600 J energy in 30 second is

(a)2 W (b) 200 W (c) 1800 W (d) 2000 W



ix. The net resistance of the above resistors is

(a) 30 Ω (b) 15 Ω (c) 60 Ω (d) 40 Ω

x. The physical quantity which is equal to V/I is

(a) resistivity (b) power (c) electrical energy (d) resistance

2. Define the following:

(i) Electrical current (ii) Electric potential difference (iii) Electric power (iv) Resistance (v) Electricity

(vi) Conductor (vii) Insulator

3. State Ohm’s law.

4. State Joule’s law of heating.

5. What is the resistivity of a material?

6. What does an electric circuit mean?

7. Define the unit of current.

8. Name a device that helps to maintain a potential difference across a conductor.

9. What determines the rate at which energy is delivered by a current?

II. SHORT ANSWER QUESTIONS (2 MARKS)

(Answer the questions in about 30 words)

1. On what factors does the resistance of a conductor depend?

2. What will happen to the current when it flows through a thick wire and thin wire of same material

connected to the same source?

3. Why are the coil of electric toasters and electric irons made of an alloy rather than pure metal?

4. Among iron and mercury, which is the better conductor of electricity and why?

5. What are the advantages of connecting electrical devices in parallel with the battery instead of

connecting them in series?

6. How is voltmeter connected in a circuit to measure the potential difference between two points?

7. Why does an electrician wear rubber gloves while working with electrical devices?

8. What is the need of an external potential difference despite the fact that electrons are in a state of

motion inside the atoms?

9. Why are fluorescent tubes used instead of bulbs?

10. Why are gases like argon and nitrogen filled in electric bulbs?

11. Calculate the number of electrons constituting one coulomb of charge.

12. What is meant by saying that the potential difference between two points is 1 V?

13. Why does the cord of an electric heater not glow while the heating element does?

14. Nichrome wire of length l and radius r has resistance of 10 Ω. How would the resistance of the wire

change when: (i) only length of the wire is doubled? (ii) only diameter of wire is doubled? Justify your

answer.

15. State the factors on which the resistance of a cylindrical conductor depends at a given temperature.

16. What is meant by the statement that the resistance of a wire is 1 Ω?

17. What combination is used for connecting in the circuit to measure the potential difference across two

points?

18. List two differences between a voltmeter and an ammeter.

19. Resistance of an incandescent filament of a lamp is comparatively much more than that when it is at

room temperature. Why?

20. State differences between kilowatt and kilowatt hour.

21. How are resistance connected so that the equivalent resistance in physical quantity remains same in such

case?

22. Amongst iron, silver, nichrome, tungsten and copper, which metal/alloy should be used to make the

(i) heating element of electric geysers



(ii) filament of incandescent bulbs

23. Give the significance of electric meter in a domestic circuit.

24. Though same current flows through the electric wires and the filament of bulb, yet only the filament

glows. Why?

25. under which conditions charges can move conductor?

26. List three factors on which amount of heat H produced in a resistor due to an electric current depends.

Also, express it mathematically.

27. Name the define commercial unit of energy. Relate it to SI unit of energy.

28. How is an ammeter and a voltmeter connected in an electric circuit?

29. State the advantages of connecting electrical devices in parallel instead of connecting them in series with

the battery.

30. Keeping the potential difference constant, the resistance of a circuit is doubled. By what factor does the

current change in the circuit?

III. SHORT ANSWER QUESTIONS (3 MARKS)


1. Show how would you connect three resistors, each of 6 Ω, so that the combination has a resistance of (i)

9 Ω (ii) 4 Ω. Justify your answer.

2. Let the resistance of an electrical component remain constant while the potential difference across the

two ends of the component decreases to half of its former vale. What change will occur in the current

through it?

3. How much work is done in moving a charge of 2 C, across two points having a potential difference of 12

V?

4. Will current flow more easily through a thick wire or a thin wire of the same material when connected to

the same source? Why?

5. Draw the symbols of following components used in circuit diagrams.

(i) electric cell (ii) battery (iii) plug key (open) (iv) plug key (closed) (v) wire joint (vi) wire crossing

without joining (vii) electric bulb (viii) a resistor (ix) variable resistance (x) ammeter (xi) voltmeter (xii)

conductor

6. Draw a schematic diagram of a circuit consisting of a battery of a three cells of 2 V each, a 5 Ω resistor or

8 Ω resistor and a plug key, all connected in series.

7. How can three resistors of resistances 2 Ω, 3 Ω and 6 Ω be connected to give a total resistance of (i) 4 Ω,

(ii) 1 Ω?

8. What is the cause of electrical resistance in a conductor?

9. (i) Two identical resistors, each of resistance 10 Ω, are connected in (a) series (b) parallel to a 6 V battery.

Calculate the ratio of power consumed in the combination of resistors in two cases.

(ii) draw the circuit diagram of the two cases.

10. State any two factors on which the resistance of a cylindrical conductor depends. Compare the resistance

of a conductor of length ‘l’ and area of cross-section ‘a’ with that of another conductor of same material

but of length and area of cross-section half and double respectively of the farmer.

11. Explain the term heating effects of electric current. Derive an expression for the heat produced by electric

current and state Joule’s law.

12. Why does the cord of an electric heater not glow while the heating element does?

13. Write the SI unit of resistance and define it. Match the correct range of resistivity with the materials

given.

(i) Conductors (a) 10-6 Ω

(ii) Alloys (b) 1012 to 1017 Ω

(iii) Insulators (c) 10-6 to 10-8 Ω



14. Write one differences between direct current and alternating current. Which one of the two is mostly

produced at power stations in our country. Name one device which provides alternating current. State

one important advantage of using alternating current. State the frequency of power supply generated in

India.

15. Two identical wires, one of nichrome and the other of copper, are connected in series and a current (I) is

passed through them. State the change observed in the temperature of the two wires. Justify your

answers. State the law which explains the above observation.

16. (i) Distinguish between an open and as closed circuit.

(ii) Name the instrument used to measure electric current. How it is connected in a circuit?

(iii) state the direction of conventional current.

17. Two identical resistors are first connected in series and then in parallel. Find the ratio of equivalent

resistance in two cases.

18. Two identical wires are first connected in series and then in parallel to a source of supply. Find the ratio of

the heat produced in the case.

IV. NUMERICAL PROBLEMS (2 OR 3 MARKS)

1. How much energy is given to each coloumb of charge passing through a 6 V battery?

2. Judge the equivalent resistance when the following are connected in parallel-(i) 1 Ω and 106 Ω (ii) 1 Ω and

103 Ω and 106 Ω.

3. An electric lamp of 100 Ω, a toaster of resistance 50 Ω and a water filter of resistance 500 Ω are

connected in parallel to a 220 V source. What is the resistance of an electric iron connected to the same

source that takes as much current as all the three appliances, and what is the current through it?

4. What is the highest and lowest total resistance that can be secured by the combination of four coils of

resistance 4 Ω, 8 Ω, 12 Ω and 24 Ω.

5. An electric iron consumes energy at a rate of 840 Ω when heating is maximum and 360 Ω when the

heating is minimum. The voltage is 220 V. what is the current and the resistance in each case?

6. Compute the heat generated while transferring 96000 coulombs of charge in one hour through a

potential difference of 50 V.

7. An electric iron of resistance 20 Ω draws a current of 5 A. calculate the heat developed in 30 seconds.

8. An electric motor draws 5 A from 220 V line. Determine the power of the motor and energy consumed in

2 h.

9. A hot plate of an electric oven is connected to a 220 V line, has two resistance coils A and B, each of 24 Ω

resistance, which may be used separately, in series or in parallel. What are the currents in the three

cases?

10. A copper wire has diameter 0.5 mm and resistivity of 1.6 x 10-8 Ωm. what will be the length of this wire to

make resistance 10 Ω? How much does the resistance change if the diameter is doubled?

11. A wire of resistance 20 Ω is bent in the form of a closed circle. What is the effective resistance between

two points at the ends of any diameter of the circle?

12. A 12 V battery is connected in the arrangement of resistance given alongside:

(i) calculate the total effective resistance of the circuit.

(ii) the total current flowing in the circuit.



13. In a factory, an electric bulb of 500 watt is used for 2 hours and an electric motor of 0.5 horse power is

used for 5 hours every day. Calculate the cost of using the bulb and the motor for one year, if the cost of

electrical energy is Rs 3 per unit.

14. Two circuits I and II are shown below. In circuit I the key is closed and in circuit II the key is open.

Compare the currents in the two circuits.

15. Electric lamps designed for use on a 220 V electric supply are rated 10 W each. Calculate the number of

lamps that can be connected in parallel to each other across the two wires of 220 V line if the maximum

allowed current is 5 A.

16. The vale of current I flowing in a given resistor for the corresponding values of potential difference V

across the resistor are given below:

I (Amperes) 0.5 1.0 2.0 3.0 4.0

V (Volts) 1.6 3.4 6.7 10.2 13.2

Plot a graph between V and I and calculate the resistance of that resistor.

17. When a 12 V battery is connected across an unknown resistor, there is a current of 2.5 mA in the circuit.

Find the value of the resistance of the resistor.

18. How many 176 Ω resistor (in parallel) are required to carry 5 A on a 220 V line?

19. Several electric bulbs designed to be used on a 220 V electric supply line are rated 10 W. how many

electric bulbs can be connected in parallel with each other across the two wires of 220 V line if the

maximum allowable current id 5 A?

20. Compare the power used in the 2 Ω resistor in each of the following circuit:

(i) a 6 V battery in series with 1 Ω and 2 Ω resistors, and

(ii) a 4 V battery in parallel with 12 Ω and 2 Ω resistors.

21. Two lamps, one rated 100 W at 220 V and the other 60 W at 220 V are connected in parallel to electric

mains supply. What current is drawn from the line if the supply voltage is 220 V?

22. Which will consume more energy, a 250 W TV set in 1 hour or a 1200 W toaster in 10 minutes?

23. An electric heater of resistance 8 Ω draws 15 A from the service mains in 2 hours. Calculate the rate at

which heat is developed in the heater.

24. An electric heater rated 800 W operates 6 hours/day. Find the cost of energy to operate it for 30 days at

Rs 3.00 per unit.



25. How much current will an electric bulb draw from 220 V source of the resistance of the bulb is 1200 Ω? If

in place of bulb, a heater of resistance 100 Ω is connected to the source, calculate the current drawn by it.

26. An electric bulb is connected to a 200 V generator. The current is 0.5 A. what is the power of the bulb?

27. For the circuit diagram given alongside, calculate:

(i) value of current flowing through each resistor

(ii) total current in the circuit

(iii) total effective resistance of the circuit.

28. FIND OUT THE READING OF AMMETER AND VOLTMETER IN THE CIRCUIT GIVEN BELOW:

29. A battery of 12 V is connected to a series combination of resistors 3 Ω, 4 Ω, 5 Ω and 12 Ω. How much

current would flow through the 12 Ω resistor?

30. The potential difference between the terminals of an electric heater is 60 V when it draws current of 4 A

from the source. What current will the heater draw if the potential difference is increased to 120 V?

31. An electric iron consumes energy at a rate of 840 W when heating is at the maximum and 360 W when

the heating is at the minimum. The voltage at which it is running is 220 V. what si the current and

resistance in each case?

32. Calculate the work done in moving a charge of 2 coulombs across two points having a potential difference

of 12 V.

33. Calculate (i) the highest and (ii) the lowest resistance that can be obtained by the combination of four

coils of resistances 4 Ω, 8 Ω, 12 Ω and 24 Ω?

34. In a household 5 tubelights of 40 W each are used for 5 hours and an electric press of 500 W for 4 hours

every day. Calculate the total electrical energy consumed by these appliances in a month of 30 days.

35. An electric charge of 3000C flows through a circuit of 10 minutes. Find the current that flows in the circuit.

36. Compare the power used in the 2 Ω resistor in each of the following circuit:

(i) a 6 V battery in series with 1 Ω and 2 Ω resistors, and

(ii) a 4 V battery in parallel with 12 Ω and 2 Ω resistors.

37. A 6 Ω resistance wire is doubled by folding. Calculate the new resistance.

38. Resistance of a metal wire of length 25 cm is 6.5 Ω. If the diameter of the wire is 0.3 mm, calculate the

resistivity of the metallic wire.

39. In the given circuit, resistors A and B made of the same metal are of the same length but A is thicker than

B. which of the two ammeters will show a higher reading? Justify your answer.

40. A hot plate of an electric oven is connected to a 220 V line. It has two resistance coils A and B each of 30

Ω resistance which may be used separately in series or in parallel. Find the value of the current required

in each of the three cases.

V. LONG ANSWER QUESTIONS (5 MARKS)

1. State and verify the law of combination of resistance.

2. Explain the following:

(i) Why is tungsten used almost exclusively for filament of electric lamps?



(ii) Why are the conductors of an electric heating devices, such a bread-toaster and electric irons, made of

an alloy rather than a pure metal?

(iii) Why is the series arrangement not used for domestic circuits?

(iv) How does the resistance of a wire vary with its area of cross-section?

(v) why are copper and aluminium wires usually employed for electricity transmission?

3. (i) Calculate the resistance of the wire using the graph.

(ii) DEFINE ELECTRIC POWER.

(iii) Derive relation between power, potential difference and resistance.

(iv) what is meant by the statement that the rating of a fuse in a circuit is 5 A?

4. Given that R1 = 100 Ω, R2 = 40 Ω, R3 = 30 Ω, R4 = 20 Ω and RA is the parallel combination of R1 and R2

whereas RB is the parallel combination R3 and R4. Combination RA is connected to the positive terminal of

12 V battery while combination RB is connected to the negative terminal. Ammeter A is connected

between the resistors RA and Rb.

(i) Find RA and RB. also calculate total resistance in the circuit.

(ii) draw the circuit diagram showing above combination connected to battery and ammeter.

5. (i) The temperature of the filament of bulb is 27000C when it glows. Why does it not get burnt up at such

a high temperature?

(ii) The filament of an electric lamp, which draws a current of 0.25 A is used for 4 hours. Calculate the

amount of charge flowing through the circuit.

(iii) an electric iron is rated 2 kW at 220 V. calculate the capacity of the use that should be used for the

electric iron.

Magnetic effects of electric current



Magnet and magnetism: The substances which have the property of attracting small pieces

of iron, nickel, cobalt, etc. are called magnets and this property of attraction is called

magnetism.

Natural magnets: Natural magnets are piece of lodestone, which is a black iron ore (Fe3O4)

called magnetite.

Origin of the word magnetism

Natural magnets called lodestones were found as early as the sixth century B.C. in the

province of Magnesia in ancient Greece, from which the word magnetism derives its name.

Magnetic poles: These regions of concentrated magnetic strength inside the magnet just near

its ends are called magnetic poles.

The end of a freely suspended magnet which points towards north is called the North Pole

while its end pointing towards south is called South Pole.

Basic properties of magnets

1) Attractive property: A magnet attracts small pieces of iron, cobalt, nickel, etc.

2) Directive property: A freely suspended magnet aligns itself nearly in the north-south

direction.

3) Law of magnetic poles: Like magnetic poles repel and unlike magnetic poles attract

each other.

4) Magnetic poles exist in pairs: If we break a magnet into two pieces, we always get two

small dipole magnets. It is not possible to obtain an isolated N-pole or S-pole.

Artificial magnets: Pieces of iron and other magnetic materials can be made to acquire the

properties of natural magnets. Such magnets are called artificial magnets.

Uses of magnets:

1) Magnets are used in radio and stereo speakers.

2) They are used in almirah and refrigerator doors to snap them closed.

3) They are used in video and audio cassette tapes, on the hard discs and floppies for

computers.

4) In children's toys.

5) In medicine, the magnetic resonance imaging (MRI) scanners expose the inner parts of

the patient's body for detailed examination by doctors.

Compass needle. It consists of a small and light magnetic needle pivoted at the centre of a

small circular brass case provided with a glass top, as shown in Fig. The ends of the compass

needle point approximately towards north and south directions. The end pointing towards

north is called North Pole and that pointing towards south is called South Pole. The north pole

of the needle is generally painted black or red.

MAGNETIC FIELD AND FIELD LINES

Magnetic Field

Define: The space surrounding a magnet in which magnetic force is exerted, is called a

magnetic field.

Direction: The direction of magnetic field at a point is the direction of the resultant force

acting on a hypothetical north pole placed where it is placed.

Magnetic Field Lines

Define: The path traced by a north magnetic pole free to move under the influence of a

magnetic field is called a magnetic field line.



Other name of magnetic field lines: The magnetic field lines are also known as magnetic

lines of force.

What does the direction of magnetic field lines at any point tells us: The direction of

tangent drawn on a magnetic field line at any point gives the direction of the magnetic

force on a north pole placed at that point.

Direction of magnetic field line (outside the bar magnet): Since the direction of

magnetic field line is the direction of force on a north pole, so the magnetic field lines

always begin form the N- pole of a magnet and end on the S- pole of the magnet.

Direction of magnetic field line (inside the bar magnet): Inside the magnet, however, the

direction of magnetic field lines is from the S- pole of the magnet to the N- pole of the magnet.

Thus, the magnetic field lines are closed curves.

Methods of plotting lines of force. The following two methods are used for drawing lines of

force of a bar magnet: (i) Iron-filings method. (ii) Compass needle method.

IRON-FILINGS METHOD

Place a card (thick, stiff paper) over a strong

bar magnet. Sprinkle a thin layer of iron

filings over the card with the help of a

sprinkler, and then tap the card gently. The

iron filings arrange themselves in a regular

pattern.

This arrangement of iron filings gives us a

rough picture of the pattern of magnetic field

produced by a bar magnet.

How does iron fillings arrange themselves to represent the magnetic field patterm

around the bar magnet?

The bar magnet exerts a force of magnetic field all around it. The iron filings experience the

force of magnetic field of the bar magnet. The force magnetic field of the bar magnet makes

the iron filings to arrange themselves in a particular pattern. Actually, under the influence

of the magnetic field of the bar magnet, the iron filings behave like tiny magnets and align

themselves along the directions of magnetic field lines. Thus, iron filings show the shape of

magnetic field produced by a bar magnet by aligning themselves with the magnetic field

lines.

Properties (or characteristics) of the Magnetic Field Lines

The magnetic field lines originate from the north pole of a magnet and end at its south

pole.

The magnetic field lines come closer to one another near the poles of a magnet but they are

widely separated at other places.

The magnetic field lines do not intersect (or cross) one another.

How can we say that magnetic force is stronger near the poles of magnet than at other

places near the magnet?

The magnetic field lines of the magnet comes near teach other near the poles and they are

widely separated at other places, due to the more number of magnetic field lines near the

poles and less number of magnetic field lines at other places, the magnetic force is stronger at

poles than at other places



Why magnetic field lines cannot intersect each other?

This is due to the fact that the resultant force on a north pole at any point can be only in one

direction. But if the two magnetic field lines intersect one another, then the resultant force on

a north pole placed at the point of intersection will be along two directions, which is not

possible.

COMPASS NEEDLE METHOD.

Magnetic Field of Earth

How can we show that earth

behaves like a magnet: A

freely suspended magnet

always points in the north –

south direction even in the

absence of any other magnet.

This suggests that the earth

itself behaves as a magnet

which causes a freely

suspended magnet (or

magnetic needle) to point

always in a particular

direction: north and south.

Shape of earth’s magnet: The

shape of the earth‟s magnetic

field resembles that of an

imaginary bar magnet of length

one – fifth of earth‟s diameter buried at its centre.

Poles of earth’s magnet: The south pole of earth‟s magnet is in the geographical north

because it attracts the north pole of the suspended magnet. Similarly, the north pole of

earth‟s magnet in the geographical south because it attracts the south pole of the

suspended magnet. Thus, there is a magnetic S- pole near the geographical north, and a

magnetic N- pole near the geographical south.



Why the freely suspended magnet makes an angle of 15 with the geographical axis

of earth: The axis of earth‟s magnetic field is inclined at an angle about 15 with the

geographical axis. Due to this a freely suspended magnet (or magnetic needle) makes an

angle of about 15 with the geographical axis and points approximately in the north- south

directions at a place.

Reason of earth’s magnetism: The earth‟s magnetism is due to the magnetic effect of

current (which is flowing in the liquid core at the centre of the earth). Thus, earth is a huge

electromagnet.

Magnetic Field Due to a Current in a Conductor

An activity to show that a wire carrying an electric current behaves like a magnet

Danish physicist H.C. Oersted was the first to demonstrate in 1820 that a current carrying

conductor produces a magnetic field around it.

Take a straight thick copper wire and place it between the

points X and Y in an electric circuit as shown in Fig.

Place a small compass near to this copper wire. See the

position of its needle.

Pass the current through the circuit by inserting the key

into the plug.

As we pass current though the copper wire XY, the compass needle gets deflected from its

position of rest. Since a magnetic needle can be deflected only by a magnetic field, so the

current carrying wire produces a magnetic field around it or it behaves like a magnet.

A current carrying conductor produces a magnetic field around it. This effect is called

magnetic effect of current.

How can detect the position of wires in wall using a magnetic compass?

A concealed current carrying conductor can be located due to the magnetic effect of current by

using a plotting compass. For example, if a plotting compass is moved on a wall, its needle will

show deflection at the place where current – carrying wire is concealed.

On what factor does the Magnetic Field Patterns Produced by current – carrying

conductors depends?

The pattern of magnetic field (or shape of magnetic

field lines) produced by a current conductor depends

on its shape.

Magnetic Field Pattern due to straight Current –

Carrying Conductor (Straight Current – carrying

Wire)

Magnetic field pattern: The magnetic field lines

around a straight conductor (straight Wire) carrying

current are concentric circles whose centers lie on

the wire.

Relation between the direction of current and

direction of magnetic field lines: When current in

the wire flows in the upward direction, then the

lines of magnetic field are in the anticlockwise



direction. If the direction of current in the wire is reversed, the direction of magnetic field

lines also gets reversed.

Factors on which the magnetic field produced by a straight current carrying

conductor depends:

1. If we increase the current in the conductor, the deflection of the compass needle

increases. This shows that, the magnitude of the magnetic field produced at a given

point is directly proportional to the current passing through the wire.

2. For a given current, if we move the compass needle away from the wire, its deflection

decreases. This shows that the magnitude of the magnetic field produced by a given

current in the wire is inversely proportional to the distance from the wire.

To know the direction of magnetic field we follow these rules

1) Right hand thumb rule: If the current carrying conductor is held in the right hand

such that the thumb points in the direction of the

current, then the direction of the curl of the fingers

will give the direction of the magnetic field, as shown

in Fig.

2) Maxwell's cork screw rule: If a right handed screw

be rotated along the wire so that it advances in the

direction of current, then the direction in which the

screw rotates gives the direction of the magnetic field

as shown in Fig.

Magnetic Field Pattern due to a circular Loop (or Circular Wire) Carrying Current

Magnetic field pattern: The magnetic field lines are circular near the current – carrying

loop. As we move away, the concentric circles representing magnetic field lines become

bigger and bigger. At the centre of the circular loop, the magnetic field lines are straight.

Factors affecting the magnitude of magnetic field produced by a current – carrying

circular loop (or circular wire) at its centre:

1) Directly proportional to the current passing through the circular loop (or circular wire.

If current flowing through circular loop increases then magnetic field becomes strong

and vice versa.

2) Inversely proportional to the radius of circular loop (or circular wire). If radius of

circular loop decreases then magnetic field at the center of loop increases.



Clock Face Rule to determine the polarity of any face of a circular current loop

If the current around the face of circular wire (or

coil) flows in the clockwise direction, then that

face of the circular wire (or coil) will be south -

pole (S-pole).

If the current around the face of circular wire (or

coil) flows in the Anticlockwise direction, then

that face of circular wire (or coil) will be a North

pole (N-pole)

Magnetic Field due to a Solenoid

Define: The solenoid is a long coil containing a

large number of close turns of insulated copper

wire.

Magnetic field pattern: The magnetic field produced by a current – carrying solenoid is

similar to the magnetic field produced by a bar magnet.

Magnetic field inside the solenoid: The magnetic field lines inside the solenoid are in the

form of parallel straight lines. This indicates that the strength of magnetic field is the same

at all the points inside the solenoid. If the strength of magnetic field is just the same in a

region, it is said to be uniform magnetic field.

Poles of solenoid: the face of solenoid where the current is clockwise that face acts like

south pole and the face of solenoid where the current is anticlockwise that face acts like

north pole.

How can we detect the poles of solenoid: We bring the north pole of a bar magnet near

both the ends of a current – carrying solenoid. The end of solenoid which will be repelled

by the north pole of bar magnet will be its north pole, and the end of solenoid which will be

attracted by the north pole of bar magnet will be its south pole.

Factors affecting the strength of magnetic field produced by a current carrying

solenoid:



1) The number of turns in the solenoid. Larger the

number of turns in the solenoid, greater will be the

magnetism, produced.

2) The strength of current in the solenoid. Larger the

current passed through solenoid, stronger will be the

magnetic field produced.

3) The nature of „‟core material‟‟ used in making solenoid.

The use of soft iron rod as core in a solenoid produces

the strongest magnetism.

4) Diameter of coil. If the diameter of coil decreases then magnetic field strength increases.

Electromagnet: A soft iron core placed inside a solenoid behaves like a powerful magnet when

a current is passed through the solenoid. This device is called an electromagnet.

When the current is switched off, the iron core loses its magnetism and so it is no longer an

electromagnet. Thus, electromagnets are temporary magnets.

Factors on which the strength of an electromagnet depends:

1) Number of turns in the coil. The larger the number of turns in the coil, greater is the

strength of the electromagnet.

2) Strength of the current. The larger the current passed through the solenoid, more

powerful is the electromagnet.

3) Nature of the core material. The core of the magnetic material like soft iron increases

the strength of the electromagnet.

Uses of electromagnets

Cranes and lifts use electromagnets to separate and lift large quantities of iron scrap

and steel

We find them in electrical devices like electric bells, telegraphs, telephones, loud

speakers, electric trains, electric motors and so on

Doctors use weak electromagnets to remove steel splinters from the eye

Differences between an electromagnet and a permanent magnet

Electromagnet Permanent Magnet

1. It is a temporary magnet. It shows

magnetism only as long as the current is

through its coil.

1. It retains magnetism for a long time

even after the removal of the magnetizing

field (or current).

2. It can produce very strong magnetic

field.

2. It produces a much weaker field than

an electromagnet.

3. The strength of an electromagnet can

be easily varied by changing the strength

of current or number of turns in the coil.

3. Its strength cannot be changed,

4. The polarity of an electromagnet can be

reversed by sending the current in reverse

direction.

The polarity of a permanent magnet

cannot be changed.

Advantages of electromagnets over permanent magnets

1) An electromagnet can produce a very strong magnetic field.



2) The strength of the magnetic field of an electromagnet can be increased/decreased by

increasing/decreasing the strength of current or the number of turns in the solenoid.

3) The polarity of an electromagnet can be reversed by sending the current in the reverse

direction.

MAGNETISM IN HUMAN BEINGS

Define ionic currents and why they are produced: Extremely weak electric currents are

produced in the human body by the movement of charged particles called ions. These are

called ionic currents.

Magnetic field produced in our body: When the weak ionic currents flow along the nerve

cells, they produce magnetic field in our body. When we try to touch something with our

hand, our nerves carry electric impulse to the appropriate muscles. And this electric

impulse creates a temporary magnetism in the body.

Organs of body where magnetic field is produced: The two main organs of the human

body where the magnetic field produced is quite significant are the heart and the brain.

Principle of MRI: The magnetism produced inside the human body (by the flow of ionic

currents) forms the basis of a technique called Magnetic Resonance Imaging (MRI) which is

used to obtain images (or pictures) of the internal parts of our body.

Uses: Magnetism has an important use in medical diagnosis because, through MRI scans,

it enables the doctors to see inside the body. For example, MRI can detect cancerous tissue

inside the body of a person.

FORCE ON CURRENT – CARRYING STRAIGHT CONDUCTOR PLACED IN A MAGNETIC

FIELD

A magnet exerts a mechanical force on a current – carrying wire, and if the free to move,

this force can produce a motion in the wire.

Discoverer and his discovery: In 1821, Faraday discovered that: When a current –

carrying conductor is placed in a magnetic field, a mechanical force is exerted on the

conductor which can make the conductor move.

Direction of force exerted on current carrying wire: The direction of force acting on a

current – carrying wire placed in a magnetic field is (i) perpendicular to the direction of

current, and (ii) perpendicular to the direction of magnetic field.

When the maximum force exerted on a current carrying wire: The maximum force is

exerted on a current – carrying conductor only when it is perpendicular to the direction of

magnetic field.

When no force exerted on a current carrying wire: No force acts on a current – carrying

conductor when it is parallel to the magnetic field.

How the direction of force on a current – carrying conductor can be reversed:

1) The direction of force on a current – carrying conductor placed in a magnetic field can

be reversed by reversing the direction of current flowing in the conductor.

2) The direction of force on a current – carrying conductor placed in a magnetic field can

also reversed by reversing the direction of magnetic field.

Fleming’s Left – Hand Rule for the Direction of Force

Statement: Hold the forefinger, the centre finger and the

thumb of your left hand at right angles to one another.

Adjust your in such a way that the forefinger points in the

direction of magnetic field and the centre finger points in



the direction of current, then the direction in which thumb points, gives the direction of

fore acting on the conductor.

Q. When is the force exerted on a current-carrying conductor (i) maximum and (ii)

minimum?

Ans. (i) When the current-carrying conductor is held perpendicular to the direction of the

magnetic field, the force exerted on it is maximum.(ii) When the current-carrying conductor is

held parallel to the direction of the magnetic field, the force exerted on it is minimum or zero.

Q.A current carrying straight conductor is placed in east-west direction. What will be

the direction of the force experienced by this conductor due to earth's magnetic field?

How will this force get affected on?(i) Reversing the direction of flow of current ? (ii)

Doubling the magnitude of current?

Ans. The direction of earth's magnetic field is from geographical south to geographical north.

According to Fleming's left hand rule, the current carrying straight conductor placed in east-

west direction will be deflected downwards. (i) On reversing the direction, the conductor is

deflected in the upward direction. (ii) If the magnitude of current is doubled, it will result in

doubling the magnitude of the force.

Q. On what factors does the force experienced by a current carrying conductor placed in

a uniform magnetic field depend?

Ans. Factors on which the force experienced by a current carrying conductor placed in a

magnetic field depends. If a current / is flowing along the wire of length L which is placed

perpendicular to the direction of the magnetic field B, then the force F experienced by the wire

perpendicular to the current and the magnetic field (as given by Fleming's left hand rule) is

expressed as: F = BIL, Thus, F depends on current /, length L and strength of field B.

THE ELECTRIC MOTOR

Define: A motor is a device which converts electrical energy into mechanical energy.

Motion of which part of motor is used in various appliances: Every motor has a shaft

or spindle which rotates continuously when current is passed into it. The rotation of its

shaft is used to drive the various types of machines in homes and industry.

Uses: Electric motor is used in electric fans, washing machines, refrigerators, mixer and

grinder, electric cars and many other appliances.

Principle of a Motor: A motor works on the principle that when a rectangular coil is

placed in a magnetic field and current is passed through it, a force acts on the coil which

rotates it continuously.

ELECTRIC MOTOR

Electric motor. An electric motor is a rotating device which converts electric energy into mechanical energy. Principle. An electric motor works on the principle that a current carrying conductor placed in a magnetic field experiences a force, the direction of force is given by Fleming's left hand rule. Construction. I. Field magnet. It is a strong horse shoe type magnet with concave poles. II. Armature. It is a rectangular coil ABCD having a large number of turns of thin insulated copper wire wound over a soft iron core. The armature is placed



between the poles the field magnet and it can be rotated about an axis perpendicular to the magnetic field les. III. Split ring commutator. It consists of a cylindrical metal ring split into two halves S1 and S2. The two ends A and D of the armature coil are connected to the split rings S1 and S2 respectively. As the coil rotates, the split rings also rotate about the same axis of rotation. The

function of the split ring commutator is to reverse the direction of current in the coil after every half rotation. IV. Brushes. Two graphite or flexible metal rods maintain a sliding contact with split rings S1

and S2, alternately. V. Battery. A battery of few cells is connected to the brushes. The current from the battery flows to the armature coil through the brushes and the split rings.

Working of a DC Motor

When the coil is powered, a magnetic field is generated around the armature. The left side of

the armature is pushed away from the left

magnet and drawn towards the right, causing rotation.

When the coil turns through 900, the brushes lose contact with the commutator and the

current stops flowing through the coil.

However the coil keeps turning because of its own

momentum.

Now when the coil turns through 1800, the sides get interchanged. As a result the commutator ring C1 is now in contact with brush B2 and commutator ring C2 is in contact with brush B1. Therefore, the current continues to flow in the

same direction.

The Efficiency of the DC Motor Increases by:

Increasing the number of turns in the coil Increasing the strength of the current

Increasing the area of cross-section of the coil

Increasing the strength of the radial magnetic field

An electric motor brings about rotational motion in domestic appliances such as

electric fans, washing machines, refrigerators,

mixers, grinders, blenders, computers, MP3 players,

etc.

ELECTROMAGNETIC INDUCTION: ELECTRICITY

FROM MAGNESTISM

Define: when a conductor is moved in magnetic field

then magnetic field strength linked to conductor

changes and a current in induced in conductor so as

to oppose the change in magnetic field strength. This

phenomenon is called electromagnetic induction.

Discoverer: The phenomenon of electromagnetic

induction was discovered by a British scientist



Michael Faraday and an American scientist Joseph Henry independently in 1831.

Instrument used to find the direction of current: A galvanometer is an instrument

which can be detect the presence of electric current in a circuit. It is connected in series

with the circuit. When no current is flowing through a galvanometer, its pointer is at the

zero mark. When an electric current passes through the galvanometer, then its pointer

deflects (or moves) either to the left side of zero mark or to the right side of the zero mark,

depending on the direction of current.

To Demonstrate Electromagnetic Induction by using a straight Wire and a Horseshoe –

Type Magnet

To Demonstrate Electromagnetic Induction by Using a Coil and a Bar Magnet

The concept of a fixed coil and a rotating magnet is used to produce electricity on large

scale generators of power house.

The condition necessary for the production of electric current by electromagnet induction

is that there must be a relative motion between the coil of wire and a magnet.

Observations about electromagnetic induction:

A current is induced in a coil when it is moved (or rotated) relative to a fixed magnet.

A current is also induced in a fixed coil when a magnet is moved (or rotated) relative to the

fixed coil.

No current is induced in a coil when the coil and magnet both are stationary relative to one

another.

When the direction of motion of coil (or magnet) is reversed, the direction of current

induced in the coil also gets reversed.

Factors affecting the magnitude of induced current:

By winding the coil on a soft iron core.



By increasing the number of turns in the coil.

By increasing the strength of magnet.

By increasing the speed of rotation of coil (or magnet).

Fleming’s Right – Hand rule for the Direction of Induced Current

According to Fleming‟s right – hand rule: Hold the thumb, the forefinger and the centre

finger of your right – hand at right angles to one another. Adjust your hand in such a way

that forefinger points in the direction of magnetic field, and thumb points in the direction

of motion of conductor, then the direction in which centre finger points, gives the direction

of induced current in the conductor.

ELECTRIC GENERATOR

Define: The electric generator is a machine for producing electric current or electricity.

Energy conversion: The electric generator converts mechanical energy into electrical energy.

Dynamo: A small generator is called a dynamo. For example, the small generator used on

bicycles for lighting purposes is called a bicycle dynamo.

Principal of Electric Generator: The electric generator works on the principal that when a

straight conductor is moved in a magnetic field, then current is induced in the conductor. In an

electric generator, a rectangular coil (having straight sides) is made to rotate rapidly in the

magnetic field between the poles of a horseshoe – type magnet. When the coil rotates, it cuts the

magnetic field lines due to which a current is produced in the coil.

Construction. 1. Field magnet. It is a strong horse shoe-type permanent magnet with concave poles. 2. Armature. ABCD is a rectangular armature coil. It consists of a large number of turns of insulated copper wire wound on a soft iron cylindrical core. It can be rotated about an axis perpendicular to the magnetic field of the field magnet. 3. Slip rings. These are two brass rings S1 and S2 rigidly connected to the two ends of the armature coil. As the coil rotates, slip rings also rotate about the same axis of rotation. 4. Brushes. These are two graphite rods B1 and B2 which are kept pressed against the slip rings S1 and S2. Through these brushes, the current induced in the armature coil is sent to the external circuit.

Working. As shown in Fig, suppose the armature coil ABCD is in the horizontal position. Now the coil is rotated clockwise. The coil cuts the magnetic lines of force. The arm AB moves upwards while the arm CD moves downwards. According to Fleming's right hand rule, the induced current flows from A to B in arm AB and C to D in arm CD i.e., the induced current flows along ABCD. The induced current flows in the circuit through brush B2 to Bv After half the rotation of the armature, the arm CD moves upwards and AS moves downwards. The induced current now flows in the reverse direction i.e., along DCBA. The current flows from Bx to B2. Thus the direction of current in the external circuit changes after every half rotation. Such a current which changes its direction after equal intervals of time is called alternating current. This device is called A.C. Generator.



Current is induced in a coil when the current in

the neighboring coil changes.

We can conclude that a potential difference is

produced in the coil-2 whenever the electric current through the coil-1 is changing (starting or

stopping). Coil-1 is called the primarly coil and

coil-2 is called the secondary coil. As the current

in the first coil changes, the magnetic field

associated with it also changes. Thus the

magnetic field lines around the secondary coil

also change. Hence the change in magnetic field

lines associated with the secondary coil is the

cause of induced electric current in it. This

process, by which a changing magnetic field in a

conductor induces a current in another conductor, is called electromagnetic induction.

Differences between electric motor and generator

Electric motor Generator

1. It converts electrical energy into

mechanical energy.

1. It converts mechanical energy into

electrical energy.

2. It is based on magnetic effect of current. 2. It is based on electromagnetic induction.

3. Current is supplied to the coil placed in

magnetic field by an external source of

electrical energy. As a result of it, coil starts

rotating.

3. The coil is rotated in a magnetic field by an

external arrangement. As a result, an electric

current is induced in the coil.

Direct current. A direct current is that current which flows with constant magnitude in the

same direction.

Alternating current. An alternating current is that current whose magnitude changes

continuously with time and whose direction reverses after equal intervals of time.

Advantage of AC over DC.

Only alternating voltage can be stepped up or stepped down by using a transformer. This

makes AC more suitable than DC for transmission for electric power over long distances

without much loss of energy.

Frequency of a.c. mains in India

In India, the direction of A.C. changes after every 1/100 second, i.e., the frequency of A.C. is

50 Hz.

Domestic Electric Circuits

Domestic Wiring

The electric power line enters our house through three wires- namely the live wire, the

neutral wire and the earth wire. To avoid confusion we follow a colour code for



insulating these wires. The red wire is the live wire, and the black wire is neutral. The

earth wire is given green plastic insulation.

The live wire has a high potential of 220 volts whereas the neutral wire has zero

potential. Thus the potential difference between the live wire and the neutral wire is

220-0 = 220 volts.

The earth wire is much thicker in size and is made of copper. One end of it is connected

to a copper plate buried deep under the earth. The earth connection is made to the

electric meter and then to the main switch.

In our homes, we receive supply of electric power through a main supply (mains), either

supported through overhead electric poles or by underground cables.

The live wire and neutral wire, coming from the electric pole, enter a box fitted just

outside our house which has a main fuse F1. The fuse is connected in series with the

live wire. This is done so because it is only the live wire which has a high potential of

220 volts unlike the neutral wire which carries zero potential. The fuse F1 has a high

rating of about 50 amperes. Thus it prevents any damage such as fire to the entire

electrical wiring entering the house due to short-circuit or overloading.

The two wires then enter the electricity meter which records the electrical power

consumed by us in kilowatt-hour (kWh). This meter is installed by the electric supply

Department of our city.

These two wires coming out of the meter are then connected to a main switch which is

placed in a distribution box. Another fuse F2 is placed in series with the live wire in this

box for the sake of consumer safety.

There are two separate circuits in a house namely lighting circuit and power circuit.

The lighting circuit with a 5 A fuse is used for running electric bulbs, fan, radio, TV,

tube lights etc. and the power circuit with a 15 A fuse is used for running electric

heater, electric iron, geyser, refrigerator etc as it draws more current.

The distribution circuits are always connected in parallel combination. In a parallel

circuit even if there is a fault or short-circuiting in any one line, the corresponding fuse

blows off leaving the other circuits and appliances intact and prevents damage to the

entire house.

In case short-circuit occurs in the power circuit, then the power-fuse will blow off but

our lights will continue to burn as the lighting circuit remains unaffected.

A constant voltage of the main line is available for all other electrical appliances.

Along with the two wires, a third wire called the earth wire also enters our house as

shown in the fig. The earth connection is first made to the electric meter and then to

the main switch. This wire then goes into the rooms along with the live and neutral

wires.



Why all switches are put in live wire: All the electrical appliances are provided with separate

switches. All the switches are put in the live wire, so that when we switch off an electrical

appliances (like an electric iron), then its connection with the live wire is cut off and there will

be no danger of an electric shock if we touch the metal case of the electrical appliances. If,

however, we put switches in the neutral wire, then the live wire will be in connection with the

electrical appliances even when the switch is in the off position, and there is a danger of an

electric shock.

SAFETY DEVICES IN HOUSEHOLD CIRCUITS

Earthing of Electrical Appliances

Why earthing is needed: To avoid the risk of electric shocks, the metal body of an electrical

appliances is earthed’. Earthing means to connect the metal case of electrical appliances to the

earth (at zero potential) by means of a metal wire called “earth wire”.

How earth wire is connected in the house hold circuit: One end of the earth wire is buried in

the earth. We connect the earth wire to the metal case of the electrical appliances by using a

three – pin plug.

What will happen if we accidentally touch the earthed appliance: If by chance, the live wire

touches the metal case of the electric iron (or any other appliances), which has been earthed,

then the current passes directly to the earth through the earth wire. It does not need our body

to pass the current and, therefore we do get an electric shock.

What kind of appliances are earthed: We give earth connections to only those electrical

appliances which have metallic body, which draw heavy current, and which we are liable to

touch.

Why we don’t do earthing of bulbs and tube lights: We, however, do not do earthing of an

electric bulb or a tube – light because we hardly touch them when they are on. The metal

casings of the switches are, however, earthed.

Electric Fuse

What happens to the copper wire if maximum current passes through them: The electric

wires used in domestic wiring are made of copper metal because copper is a good conductor of

electricity having very low resistance. If the current passing through wires exceeds this

maximum value, the copper wires get over heated and may even cause a fire.

When a large current can flow in household circuit: An extremely large current can flow

domestic wiring under two circumstances: Short circuiting and overloading.

Short Circuiting: This touching of the live wire and neutral wire directly is known as short

circuit. When the two wires touch each other, the resistance of the circuit so formed is very,

very small very large current flows through the wires and heats the wires to a dangerously

high temperature, and a fire may be started.

Overloading: If too many electrical appliances of high power rating (like electric iron, water

heater, air conditioner, etc.,) are switched on at the same time, they draw an extremely large

current from the circuit. This is known as overloading the circuit. Due to an extremely large

current flowing through them, the copper wires of household wiring het heated to a very

high temperature and a fire may be started.

Define of fuse: A fuse is a safety device having a short length of a thin, tin- plated copper wire

having low melting point, which melts and breaks the circuit if the current exceeds a safe value.



On what factor does the thickness and length of fuse wire depends: The thickness and

length of the fuse wire depends on the maximum current allowed through the circuit.

On which law does the electric fuse work: An electric fuse works on the heating effect of

current.

Why we use thin fuse wire: We use a thin wire in a fuse because it has a much greater

resistance the rest of connecting wires. Due to its high resistance, the heating effect of current

will be much more in the fuse wire than anywhere else in the circuit. This will melt the fuse wire

whereas other wiring will remain safe.

Why we should not use thick fuse wire: We should not use a thick wire as a fuse wire because

it will have a low resistance and hence it will not get heated to its melting point easily.

Why we should not use copper wire as fuse wire: A pure copper wire cannot be used as a

fuse wire because it has a high melting point due to which it will not melt easily when a short

circuit takes place.

Disadvantage of fuse wire: A blown fuse should be replaced only after the cause of excessive

current flow has been found and removed.

What are used these days which have an advantage over fuse wire: These days more and

more houses are using ‘Miniature Circuit Breakers’ (MCBs) to protect the household wiring

from the excessive flow of electric current through it.

How does MCB work: If the current becomes too large, the miniature circuit breaker puts off a

switch cutting off the electric supply. The MCB can be re-set when the fault has been corrected.

Miniature current breaker (MCB) contains an electromagnet which, when the current exceeds

the rated value of circuit breaker, becomes strong enough to separate a pair of contacts (by

putting of a switch) and breaks the circuit. So, unlike fuses, MCBs do not work on heating effect

of current MCBs work on the magnetic effect of current.

Where fuses are used these days: Fuses are also used to protect the individual domestic

electrical appliances from damage which may be caused due to excessive current flow through

them.

Hazards of Electricity (or Dangers of Electricity)

If a person happens to touch a live electric wire, he gets a severe electric shock. In some cases,

electric shock can even kill a person.

Short – circuiting due to damaged wiring or overloading of the circuit can cause electrical fore in

a building.

The defects in the household wiring like loose connections and defective switches, sockets and

plugs can cause sparking and lead to fires.

Precautions in the Use of Electricity



If a person accidently touches a live electric wire or if an electric fir starts in the house, the main

switch should be turned off at once so as to cut off the electricity supply. This will prevent the

fire from spreading.

The person who happens to touch the live electric wire should be provided an insulated support

wood, plastic or rubber. We should never try to pull away the person who is in contact with the

live wire, otherwise we will also get a shock.

All the electrical appliances like electric iron, cooler, and refrigerator, etc. should be given

connection to save ourselves from the risk of electric shocks. Even if the earth connection is

there, we should avoid touching the metal body of an electric appliances when it is on.

All the switches should be put in the live wire of the A.C. circuit, so that when the switch is

turned off, the appliances gets disconnected from live wire and there is no risk of electric shock.

We should always be connected in the live wire of the circuit. The fuse wire should be of proper

rating and material. We should never use a copper wire (connecting wire) as fuse wire because

a copper wire has a very high current rating due to which a copper wire fuse cannot protect the

wiring against short circuiting or overloading.

The household wiring should be done by using good quality wires having proper thickness and

insulation. All the wire connections with switches, sockets, and plugs should be tight, and all the

wire joints should be covered with insulated adhesive tape. Defective switches, sockets and

plugs should be replaced immediately.

Energy: Whenever a body is capable of doing work, the body is said to possess energy.

Thus energy is defined as the ability of a body to do work and the amount of energy

Sources of Energy



possessed by a body is equal to the amount of work it can do when its energy is

released.

Units of energy: On S.I. system, energy is measured in the units of joules or in

calories and on C.G.S. system in ergs. However, the commercial unit of energy is

kilowatt-hour. The energy is said to be one kilowatt-hour, when a body consumes one

kilowatt of energy in one hour.

Sources of energy: A source of energy is that which is capable of providing enough

useful energy at a steady rate over a long period of time.

A good source of energy should be:

(i) Safe and convenient to use, e.g., nuclear energy can be used only by highly

trained engineers with the help of nuclear power plants. It cannot be used for

our household purpose.

(ii) Easy to transport, e.g., coal, petrol, diesel, LPG etc. Have to be transported

from the places of their production to the consumers.

(iii) Easy to store, e.g., huge storage tanks are required to store petrol, diesel, LPG

etc.

Characteristics of an ideal or a good fuel:

1. It should have a high calorific or a heat value, so that it can produce

maximum energy by low fuel consumption.

2. It should have a proper ignition temperature, so that it can burn easily.]

3. It should not produce harmful gases during combustion.

4. It should be cheap in cost and easily available in plenty for everyone.

5. It should be easily and convenient to handle, store and transport from one

place to another.

6. It should not be valuable to any other purpose than as a fuel.

7. It should burn smoothly and should not leave much residue after its

combustion.

Classification of sources energy:

The sources of energy can be classified as follows:

(i) Renewable (ii) Non-Renewable.

Renewable sources of energy

Renewable sources of energy are those which are Inexhaustible, i.e., which can

be replaced as we use them and can be used to produce energy again and again.

These are available in an unlimited amount in nature and develop within a

relatively short period of time.

Examples of Renewable Sources of Energy: (i)Solar energy, (ii) Wind Energy,

(iii) water energy (hydro-energy), (iv) Geothermal energy, (v) Ocean energy, (vi)

Biomass energy (firewood, animal dung and biodegradable waste from cities and

crop residues constitute biomass).



Advantages of Renewable Sources of Energy:

These sources will last as long as the Earth receives light from the sun.

These sources are freely available in nature.

These sources do not cause any pollution.

Non-Renewable Sources of Energy

Non-renewable sources of energy are those which are exhaustible and cannot be

replaced once they have been used.

These sources have been accumulated in nature over a very long period of

millions of years.

Examples of Non-renewable sources of Energy: (i) Coal, (ii) Oil and (iii) Natural

gas.

All these fuels are called fossil fuels.

Disadvantages of Non-renewable sources of Energy:

Due to their extensive use, these sources are fast depleting.

It is difficult to discover and exploit new deposits of these sources.

These sources are a major cause of environmental pollution.

Conventional and Non-conventional Sources of Energy

Sources of energy are also classified as : (i) Conventional sources of energy (ii)

Non-conventional sources of energy.

Conventional sources of energy are those which are used extensively and a

meet a marked portion of our energy requirement and these are :

Fossil fuels (coal, oil and natural gas) and

Hydro energy (energy of water flowing in rivers).

Biomass energy and wind energy also fall in this category as these are

being used since ancient times.

Non-conventional sources of energy are those which are not used as

extensively as the conventional ones and meet our energy requirement only on a

limited scale. Solar energy, ocean energy (tidal energy, wave energy, ocean

thermal energy, OTE), Geothermal energy and nuclear energy belong to this

category. These sources of energy which have been tapped with the aid of

advances in technology to meet our growing energy needs are also called

alternative sources of energy.

Wind Energy

When a large mass of air moves from one place to another it is referred as wind.

During this process kinetic energy gets associated with it which is referred to as

wind energy.

Principle of utilisation of wind energy: Wind energy is efficiently converted

into electrical energy with the aid of a windmill. A windmill is a large fan having

big blades, which rotate by the force exerted by moving wind on them. These

blades remain continuously rotating as long as wind is blowing and can be used

to drive a large number of machines like water pumps, flour mills etc. But these

days a windmill is used to generate electric current which is used for various



purposes and therefore wind power stations are established all over the world

which convert wind energy directly into electrical energy.

Uses of wind energy:

It is used to drive windmills, water lifting pumps and flour mills etc.

It is used to propel sale boats.

It is used to fly engine less aeroplanes or gliders in the air.

It is used to generate electricity used for various purposes like lightening,

heating etc.

Advantages of generating wind energy:

It is readily and abundantly available at every place of the earth free of

cost.

It is eco-friendly and does not produce any kind of environmental

pollution.

It is a renewable source as air itself is a renewable and inexhaustible

resource.

It is a cheap source of energy, as it does not involve any costly investment.

Fossil Fuels

Fossil fuels are formed by the anaerobic decomposition of the remains of

prehistoric plants and animals which got buried deep inside millions of years

ago under high pressure and temperature.

The energy of fossil fuels is in fact, that solar energy which was trapped by

natural processes a very long time ago. Coal, petroleum and natural gas are

fossil fuels.

Formation of Fossil Fuels: During its formation, an entire organism or its

parts often get buried in sand or mud. These, then decay and disintegrate

leaving no signs of their existence. Infact, the harder parts of organisms after

their death, settle down and are covered by sediments and subjected to extreme

pressure and temperature of the earth converts them into fossil fuels, the

process being referred to as fossilization.

Disadvantages of Fossil Fuels:

The fossil fuels are non-renewable sources of energy and once used

cannot be renewed.

Burning of fossil fuels causes air pollution.

The fossil fuels reserves in the earth are limited and may get exhausted

soon.

Solar Energy

The energy produced by the sun in the form of heat and light energy is called as

solar energy.

Principles of utilisation of Solar Energy: Solar energy is utilised by the

involvement of two main principles:

(i) In the appliances requiring a moderate temperature, the incident sun rays

are reflected by a plain mirror on a black container which absorbs the solar



energy and gets heated.

(ii) In the appliances requiring a high temperature, the incident sun rays are

reflected and concentrated by using a large concave reflector which focuses

all the sun rays at a single point called focus and any object kept at the

focus gets strongly heated.

Harnessing or utilisation of Solar energy: The sun is the ultimate source of

energy having a remarkable capacity to produce energy in the form of heat and

light. The energy produced by the sun in one day is about 50,000 times more

than the energy consumed in the whole world in one year. But solar energy has

certain limitations, which does not facilitate its large-scale utilisation. Solar

energy can be put to use in two differ ways.

(i) Direct utilization: Directly the solar energy can be used either by

collecting it as heat energy or by converting it into electricity.

(ii) Indirect utilization: Indirectly the solar energy can be utilized by

converting it into chemical energy like biomass or by utilising the energy

obtained from wind, sea waves, tides etc.

Solar Heating Devices

A device that gets heated by absorbing solar energy radiated by the sun in the form of

heat and light energy is called a solar heating device. For eg. Solar cooker, solar water

heater, solar furnace and solar cells are solar heating devices.

Solar cooker

A solar cooker is a device which utilises solar heat energy for cooking food

material.

Construction: It consists of an insulated wooden box (B) painted with black

from inner side. The lid of the box is provided with a plane mirror reflector (R)

and a glass sheet (G). The food to be cooked is placed in a metal container (C)

painted with black from outer side and kept in the box .The container is covered

with the glass sheet. The box is then kept in direct sunlight and its reflector is

adjusted in such a way that a strong beam of sun light falls over it.

Working: When the solar cooker is kept in direct sunlight, the reflector (R)

reflects both visible and infrared rays of the sunlight on to the top of the box in

the form of a strong beam of light. The black surface of the box and the vessel

absorbs it. When the inner black surface becomes quite hot, it also starts

radiating heat energy in the form of infrared rays, but the upper glass sheet (G)



does not allow these rays to pass through it and go outside the box. As a result,

these infrared rays get absorbed in the box, which increases its internal

temperature up to about 100C - 120C. This high temperature cooks the food

material kept in the metallic container inside the box.

Limitations of solar Cooker:

It can not be used during night.

On a cloudy day, it can not be used.

The direction of the reflector has to be adjusted according to the position

of the sun.

It can not be used for making „chappatis‟.

It can not be used for frying.

Solar cell

A solar cell is a device which converts solar energy (light energy) directly into

electricity.

Construction and working: It is made of semi-conducting material like silicon,

germanium, selenium or gallium. A modern solar cell is made from wafers of

semi conducting materials containing impurities in such a way that a potential

difference gets generated when light falls on them. A 4cm2 solar cell produces a

potential difference of about 0.4--0.5volts and generate about 60 milli-amperes

of current. To generate a large amount of current a number of solar cells are

arranged together in a definite pattern in a solar panel. The energy (electric

current) generated in a solar panel is stored in a battery connected to it and can

be used for various purposes.

Uses of a solar cell:

Solar cells are used for production of electricity for lighting, houses,

streets etc. Solar cells are used for production of electricity to run

electronic appliances like televisions, radios, watches, calculators, toys,

toy games etc. Solar cells are used to develop electricity for offshore oil

drilling platforms etc. Solar cells are used to generate electricity in

artificial satellites, rockets, and space vehicles etc.

Hydro electricity

When the water flowing in a river is stored in a high rise dam and allowed to fall

from the top of the dam. The water rushes down with a great force, which can be

utilised to drive large water turbine. These turbines are connected with electric

generators, which generate electric current. The electricity generated in this

process is termed as hydro electricity or hydel power. Infact the process involves

transference of potential energy of the water into kinetic energy and then into

electric energy.

Advantages of generating hydro electricity:

It is readily and abundantly available everywhere free of cost.

It is eco-friendly and does not produce any kind of environmental

pollution.



It is a renewable source as water itself is a renewable and inexhaustible

resource.

It is a cheap source of energy, as it does not involve any costly investment.

Energy from Oceans

The oceans acquire almost 71% of the surface of the earth and the enormous

amount of water present in them not only act as a big collector of solar heat

energy, but also store large amount of it due to its high specific heat. Thus

ocean water can be used as a renewable resource of energy.

The main forms of ocean energy are:

1. Ocean Thermal energy: The energy available due to the temperature

difference between the deeper levels and surface of an ocean is called as

ocean thermal energy.

2. Ocean Tidal energy: The rise of ocean water due to attraction of the moon

is referred to as high tide and its fall as low tide. The enormous movement

of water due to high and low tide provide a large amount of energy known

as ocean tidal energy. This tidal energy can be utilised by constructing a

tidal barrage or dam.

3. Sea wave energy: The energy obtained from the high speed sea waves is

referred to as sea wave energy. Infact these high speed sea waves have a lot

of kinetic energy associated with them, which can used to drive dynamos

which convert kinetic energy into electrical energy.

4. Energy from Nuclear deuterium of oceans: The ocean water contains

unlimited amount of heavy hydrogen isotope called deuterium which is

isotope hydrogen having one proton and one neutron in its nucleus.

Scientists are working hard to produce energy by carrying by out controlled

nuclear fission of deuterium isotope. The process is still in its experimental

stage.

5. Energy from Salinity gradient in seas: The difference in the concentration

of salts in the water of the two or more seas is called as salinity gradient.

This salinity gradient is now a day used to obtain energy with the

involvement of suitable techniques.

6. Energy from sea vegetation or biomass: Sea vegetation or biomass is

another direct source of energy because the enormous amount of sea weeds

present in the sea water provides an endless supply of methane fuel.

Limitations of Energy from Oceans:

1. Tidal Energy for which very few suitable sites are available for construction

of dams and the power generation is intermittent and not very large.

2. Wave Energy where power output is variable and the presently available

technologies are very expensive.

3. Ocean Thermal Energy where the conversion efficiency is low (3% - 4%) and

a lot of capital investment is required.

Bio-Mass

Biomass is defined as living matter or its residue and is a renewable sources of energy.

The biomass includes (i) all the new plant growth (ii) agricultural and forest residues



(like biogases, bark, sae dust, wood shavings, roots, animal droppings etc.) (iii)

Carbonaceous wastes (like sewage, garbage, night-soil, etc.) (iv) Biodegradable organic

affluent from industries.

Biogas

Biogas is a mixture of gases produced by anaerobic degradation of biomass in

the presence of water but in the absence of oxygen.

It is a renewable source of energy on account of its production from vastly and

continuously available organic wastes.

Advantages of Biogas:

A biogas plant, being quite simple, can easily be built in rural areas. A

small plant using dung from 3 to 4 heads of cattle is capable of supplying

biogas for 6 hours daily for cooking purposes.

Biogas is a clean fuel that burns without smoke and leaves no ash.

The main constituent of biogas, i.e., ethane has a higher calorific value

(55kJ/g) that of petrol (50kJ/g).

The spent slurry, being rich in nitrogen and phosphorus, is good manure.

By using biogas, firewood is saved and deforestation is reduced.

Composition of Biogas: Biogas is mainly composed methane (up to 75%), CO2

(25%) and traces of other gases such as nitrogen and hydrogen. Whereas

methane is a high value calorific fuel, carbon dioxide is an inert gas.

Biogas is prepared in biogas plants which are of two types: (i) Fixed Dome Type (ii)

Floating Gas Holder Type.

Fixed Dome Type Biogas Plant

The main parts of fixed of dome type of biogas plants are:

1. Digester: It is well shaped underground tank made of bricks. Its roof is some-

shaped which acts as a storage tank for biogas.

2. Mixing tank: It is constructed on the ground level where cattle dung and water

are mixed.

3. Inlet tank: It is constructed underground below the mixing tank.

4. Overflow tank: It is constructed slightly below the level of mixing tank.

5. Outlet tank: It is constructed below the overflow tank.



Working of Biogas Plant

Cattle dung and water are mixed in equal proportion in the mixing tank to form slurry.

This slurry is fed into the digester tank through inlet tank when the digester tank is

filled about 2/3rd of its capacity, the dome is left free for collection of biogas. The

slurry undergoes anaerobic fermentation and biogas is produced after 50 to 60 days.

As biogas is collected in the dome it exerts pressure due to which spent slurry go to

the overflow tank through outlet tank and fresh slurry is fed into the digester and

continuous supply of biogas is obtained

spent slurry is used as manure.

Geothermal energy

Geothermal energy is the heat of the earth and is the naturally occurring

thermal energy found within rock formations and the fluids held within those

formations.

Geothermal energy is one of those few sources of energy that do not come

directly or indirectly from the solar energy.

Utilization principle of geothermal energy: The underground hot water in

contact with hot spots changes into steam. As the steam is trapped between the

rocks, it gets compressed to high pressure. At some places, hot water and steam

gush out from the Earth‟s surface after making their way through large cracks

between the rocks and form natural geysers. Geothermal energy carried by

natural geysers is utilized for generating electricity.

Merits of geothermal Energy:

Geothermal energy is the most versatile and least polluting renewable

source of energy.

It can be harnessed for 24 hours throughout the year.

Geothermal energy is relatively inexpensive.

As compared to solar energy and wind energy, the power generation level

of geothermal energy is higher.

Geothermal energy can be used for power generation as well as direct

heating. In USA, water is pumped from underground hot water deposits

and is used to heat houses.

Limitations of Geothermal Energy:

Geothermal hot spots are scattered and usually some distance away from

the areas that need energy.

The overall power production has a lower efficiency (about 15%) as

compared to that of fossil fuels (35% to 40%).

Though as a whole, geothermal energy is inexhaustible, a single by ore

has a limited life span of about 10 years.

Noise pollution is caused by drilling operations at geothermal sites.

Nuclear Energy

A reaction in which the nucleus of an atom undergoes a change to form a new

atom and releases an enormous amount of energy is called as nuclear energy.

There are two distinct ways of obtaining nuclear energy. a) Nuclear fission b)



Nuclear fusion

Nuclear Fission reaction

This type of nuclear reaction was first

of all reported by Otto Hahn in 1938.

He stated that when an unstable heavy

nucleus is bombarded with slow speed

thermal neutrons, it splits into two

small stable nuclei liberates an

enormous amount of heat and light

energy.

When uranium 235 atoms are bombard

with slow moving thermal neutrons, it

breaks up into two small stable nuclei

of Barium and Krypton. The process

also produces three neutrons and an

enormous amount of heat energy and light energy. The reaction involved is

shown:

In all nuclear fission reactions, a small quantity of matter is a lot i,e., the total

mass of all the fission products is less than the total mass of the reactants. This

lost matter gets converted into energy, which is released in any nuclear fission

reaction. The energy (E) obtained due to loss of matter of mass m is given by the

famous Einstein‟s equation. E = mc2 where m is the mass of uranium and c is

the speed of light.

Nuclear Fusion reaction

This type of nuclear reaction was first of all reported by Hans Bethe in 1939.

The word „fusion‟ means „to combine together‟. So, nuclear fusion means

combining together of two or more nuclei to form a single nucleus. Thus, a

process in which two lighter nuclei fuse (combine) together to form a stable

heavier nucleus with a simultaneous release of a very large amount of energy is

called nuclear fusion. The energy produced in a fusion reaction is much higher

than that produced in a nuclear fission reaction.

Nuclear fusion takes place only at very high temperature, about 4 – 15 million

degrees (4 × 106 C – 15 × 106 C). That is why nuclear fusion is also called

thermonuclear reaction.

Advantages of Nuclear Energy

1. The advantages of nuclear energy are that:

2. It produces a large amount of useful energy from a very small amount of a

nuclear fuel (like uranium-235).

3. Once the nuclear fuel (like uranium-235) is loaded into the reactor, the nuclear

power plant can go on producing electricity for two to three years at a stretch.

There is no need for putting in nuclear fuel again and again.

4. It does not produce gases like carbon dioxide which contributes to greenhouse

effect or sulphur dioxide which causes acid rain.



Disadvantages of Nuclear Energy

1. The major hazard of nuclear power generation is the storage and disposal of

spent or used fuels – the uranium still decaying into harmful subatomic particles

(radiations).

2. Improper nuclear-waste storage and disposal result in environmental

contamination.

3. There is a risk of accidental leakage of nuclear radiation.

4. The high cost of installation of a nuclear power plant, high risk of environmental

contamination and limited availability of uranium makes large-scale use of

nuclear energy prohibitive.

Environmental consequences of the increasing demand for energy

1. The combustion for fossil fuels is producing acid rain and damaging plants

(crops), soil and aquatic life.

2. The burning of fossil fuels is increasing the amount of greenhouse gas carbon

dioxide in the atmosphere.

3. The cutting down of trees from the forest (deforestation) for obtaining fire-wood is

causing soil erosion and destroying wild life.

4. The construction of hydro-power plants is disturbing ecological balance.

5. Nuclear power plants are increasing radioactivity in the environment.

Nuclear fission Nuclear fusion

1. It involves breaking of a heavy

nucleus into lighter nuclei into a

heavy two light nuclei.

2. It is carried out by the bombardment

of thermal two lighter nuclei up to

neutrons over a heavy nucleus

3. It is a chain reaction.

4. It is a controlled process.

5. It produces an enormous amount of

energy.

6. Fission products are hazardous.

1. It involves binding of two nucleuses.

2. It is carried out by heating an

extremetemperature.

3. It is not a chain reaction.

4. It is an uncontrolled process.

5. It produces more energy than nuclear

fission.

6. It does not cause pollution.



Chemical reactions

Chemical reactions are the processes in which new substances with new properties are formed.

During a chemical reaction, atoms of one element do not change into those of another element.

Only a rearrangement of atoms takes place in a chemical reaction.

Reactants and products of a chemical reaction

The substances which take part in a chemical reaction are called reactants.

The new substances produced as a result of chemical reaction are called products.

When a magnesium ribbon is heated, it burns in air with a dazzling white flame to form a white

powder called magnesium oxide. Actually, on heating, magnesium combines with oxygen present in

air to form magnesium oxide.

Magnesium

(As ribbon)

+ Oxygen

(From air)

Heat Magnesium oxide

(White powder)

The burning of magnesium in air to from magnesium oxide is an example of a chemical reaction.

The magnesium ribbon which we use usually has a coating of ‘basic magnesium carbonate’ on its

surface which is formed by the slow action of moist air on it (Basic magnesium carbonate is a

mixture of magnesium carbonate and magnesium hydroxide MgCO3.Mg(OH)2 ). Before burning in air,

Chemical reactions and equations



the magnesium ribbon is cleaned by rubbing with a sand paper. This is done to remove the

protective layer of basic magnesium carbonate from the surface of magnesium ribbon so that it may

readily combine with the oxygen of air.

Another point to be noted is that the dazzling (very bright) white light given out during the burning

of magnesium ribbon is harmful to the eyes. So, the magnesium ribbon should be burned by keeping

it as far as possible from the eyes.

A large number of chemical reactions keep on occurring in our daily life. Souring of milk (When left

at room temperature during summer), Formation of curd from milk, cooking of food, Digestion of

food in our body, Process of respiration, Fermentation of grapes, Rusting of iron (When left exposed

to humid atmosphere), Burning of fuels (like wood, coal, kerosene, petrol and LPG), Burning of

candle wax, and Ripening of fruits, are all chemical changes which involve chemical reactions.

Characteristics of Chemical Reactions

In a chemical reaction, the substances known as reactants are converted into new substances called

products. The conversion of reactants into products in a chemical reaction is often accompanied by

some features which can be observed easily.

The easily observable features (or changes) which take place as a result of chemical reactions are

known as characteristics of chemical reactions.

The important characteristics of chemical reactions are:

1. Evolution of a gas,

2. Formation of a precipitate,

3. Change in colour,

4. Change in temperature, and

5. Change in state

Evolution of a Gas

Some chemical reactions are characterised by the evolution of a gas.

For example, when Zinc granules react with dilute sulphuric acid, then bubbles of hydrogen gas are

produced. So, the chemical reaction between zinc and dilute sulphuric acid is chracterised by the

evolution of hydrogen gas.

Zn

Zinc

+ H2SO4

Sulphuric acid

ZnSO4

Zinc sulphate

+ H2

Hydrogen

The chemical reaction between sodium carbonate and dilute hydrochloric acid is characterized by

the evolution of carbon dioxide gas.

Na2CO3

Sodium

carbonate

+ HCI

Hydrochloric

acid

NaCl

Sodium

chloride

+ CO2

Carbon

dioxide

+ H2O

Water

Formation of a Precipitate

A precipitate is a ‘solid produce’ which separates out from the solution during a chemical reaction. A

precipitate can be formed by mixing aqueous solutions (water solutions) of reactants when one of

the products is insoluble in water.



Some chemical reactions are characterized by the formation of a precipitate. For example, when

potassium iodide solution is added to a solution of lead nitrate, then a yellow precipitate of lead

iodide is formed.

2 KI (aq)

Potassium

iodide

+ Pb(NO3)2 (aq)

Lead nitrate

Pb I2 (s)

Lead iodide

(yellow ppt)

+ 2 KNO3 (aq)

Potassium nitrate

The chemical reaction between sulphuric acid and barium chloride solution is characterized by the

formation of a white precipitate of barium sulphate.

BaCI2 (aq)

Barium

chloride

+ H2SO4 (aq)

Sulphuric acid

BaSO4 (s)

Barium sulphate

(White ppt.)

+ 2HCI (aq)

Hydrogen

chloride

Change in Colour

Some chemical reactions are characterised by a change in colour.

For example, when citric acid reacts with potassium permanganate solution, then the purple colour

of potassium permanganate solution disappears (it becomes colourless).

The chemical reaction between sulphur dioxide gas and acidified potassium dichromate solution is

characterized by a change in colour from orange to green.

Change in Temperature

Some chemical reactions are characterised by a change in temperature.

For example, when quicklime (CaO) reacts with water, then slaked lime (Ca(OH)2) is formed and a lot

of heat energy is produced. This heat raises the temperature due to which the reaction mixture

becomes hot.

The reaction between quicklime and water to form slaked lime is an exothermic reaction (which

means heat producing reaction).

The chemical reaction between zinc granules and dilute sulphuric acid is also charaterised by a

change in temperature (which is rise in temperature).

The chemical reaction in which carbon burns in air to form carbon dioxide also releases a lot of heat.

The chemical reaction between barium and ammonium chloride to form barium chloride, ammonia

and water is characterised by a change in temperature (which is fall in temperature). It is

endothermic reaction (which means heat absorbing reaction).

Change in State

Some chemical reactions are characterised by a change in state.

The combustion reaction of candle wax is characterised by a change in state from solid to liquid and

gas (because wax is solid, water formed by the combustion of wax is a liquid at room temperature

whereas carbon dioxide produced by the combustion of wax is a gas).

Chemical equations

The method of representing a chemical reaction with the help of symbols and formulae of the

substances involved in it is known as a chemical equation.



Zn

Zinc

+ H2SO4

Sulphuric

acid

ZnSO4

Zinc sulphate

+

H2

Hydrogen

The substances which combine or react are known as reactants. Zinc and sulphuric acid are the

reactants here.

The new substances produced in a reaction are known as products. Zinc sulphate and hydrogen are

the products in this case.

The arrow sign pointing towards the right hand side is put between is put between the reactants and

products. This arrow indicates that the substances written on the left hand side are combining to

give the substances Written on the right hand side in the equation.

A chemical equation is a short – hand method of representing a chemical reaction.

Balanced and unbalanced Chemical Equations

A balanced chemical equation has an equal number of atoms of different elements in the reactants

and products.

A balanced chemical equation has equal masses of various elements in reactants and products.

An unbalanced chemical equation has an unequal number of atoms of one or more elements in the

reactants and products. In other words, an unbalanced equation has an unequal number of atoms of

one or more elements on its two sides.

An unbalanced equation has unequal masses of various elements in reactants and products.

‘’ Matter can neither be created nor destroyed in a chemical reaction’’. This means that the total

mass of all the reactants must be equal to the total mass of the products.

The number of various types of atoms in reactants must be equal to the number of same type of

atoms in products. It is obvious that we have to make the number of different types of atoms equal

on both the sides of a chemical equation to make. To make the number of different types of atoms

equal in reactants and products is known as balancing of an equation.

The chemical equations are balanced to satisfy the law of conservation of mass in chemical

reactions.

We should never change the formula of an element or a compound to balance an equation. We can

only multiply a symbol or a formula by figures like 2, 3, 4, etc.

To Make Equations More Informative

The chemical equations can be made more informative in three ways:

By indicating the ‘’physical states” of the reactants and products.

By indicating the ‘’heat changes’’ taking place in the reaction.

By indicating the ‘’conditions’’ under which the reaction takes place.

To Indicate the Physical States of Reactants and products in an Equation

Solid state is indicated by the symbol (s)

Liquid state is indicated by the symbol (I)

Aqueous solution (solution made in water) is indicated by the symbol (aq)

Gaseous state is indicated by the symbol (g)

Zn (s)

Zinc

+ H2SO4

Sulphuric acid

ZnSO4 (aq)

Zinc sulphate

+ H2 (g)

Hydrogen gas



Ca(OH)2 (aq)

Calcium hydroxide

(Lime Water)

+ CO2 (g)

Carbon

dioxide

CaCO3 (s)

Calcium

carbonate

(White ppt.)

+ H2O (l)

Water

To Indicate the Heat Changes in an Equation.

There are two types of reactions on the basis of heat changes involve: Exothermic reactions and

endothermic reactions.

Those reactions in which heat is evolved are known as exothermic reactions. For example, when

carbon burns in oxygen to form carbon dioxide, a lot of heat is produced in this reaction:

C (s)

Carbon

+ O2 (g)

Oxygen

CO2 (g)

Carbon dioxide

+ Heat

The burning of carbon in oxygen is an exothermic reaction because heat is evolved in this reaction.

An exothermic reactions is indicated by writing “+ Heat’’ or ‘’+ Heat energy’’ or just “+ Energy’’ on

the products side of an equation.

The burning of natural gas is an exothermic reaction because heat is produced in this reaction.

Please note that all the combustion reactions are exothermic reactions.

CH4 (g)

Methane

(Natural gas)

+ 2O2 (g)

Oxygen

(From air)

CO2 (g)

Carbon

dioxide

+ 2H2O (g)

Water

+ Heat

energy

Glucose then undergoes slow combustion by combining with oxygen in the cells of our body to

produce energy in a process called respiration. In addition to other functions, this energy maintains

our body heat.

C6H12O6 (aq)

Glucose

+ 6O2 (g)

Oxygen

6CO2 (g)

Carbon

dioxide

+ 6H2O (I)

Water

+ Energy

Respiration is an exothermic process because energy is produced during this process.

Those reactions in which heat is absorbed are known as endothermic reactions. For example, when

nitrogen and oxygen are heated to a very high temperature (of about 30000C) they combine to form

nitrogen monoxide, and a lot of heat is absorbed in this reaction:

N2 (g)

Nitrogen

+ O2 (g)

Oxygen

+ Heat 2NO (g)

Nitrogen monoxide

The reaction between nitrogen and oxygen to form nitrogen monoxide is an endothermic reaction

because heat is absorbed in this reaction.

An endothermic reaction is usually indicated by writing “+ Heat” or “Heat energy” or just “+ Energy’’

on the reactants side of an equation.

Photosynthesis is an endothermic reaction. This is because sunlight energy is absorbed during the

process of photosynthesis by green plants.

The electrolysis of water to form hydrogen and oxygen is also an endothermic reaction. This is

because electric energy is absorbed during this reaction.



To Indicate the Conditions Under Which the Reaction Takes Place

If heat is required for a reaction to take place, then the heat sign delta is put over the arrow of the

equation. If the reactions takes place in the presence of a catalyst, then the symbol or formula of the

catalyst is also written above the arrow sign in the equation.

When potassium chlorate (KCIO3) is heated in the presence of manganese dioxide catalyst, it

decomposes to form potassium chloride and oxygen gas.

2KCIO3 (s)

Potassium

Chlorate

MnO2

2KCI (s)

Potassium

Chloride

+ 3O2 (g)

Oxygen

Methanol (or Methyl alcohol) is manufactured from carbon monoxide and hydrogen. The mixture of

carbon monoxide and hydrogen gases is compressed to 300 atmospheres pressure and then passed

over a catalyst consisting of a mixture of zinc oxide and chromium oxide heated to a temperature of

300oC. So, the conditions for this reaction to take place are: a pressure of 300 atmospheres.

CO (g)

Carbon

monoxide

+ 2H2 (g)

Hydrogen

300 atm, 300oC

ZnO + CrO3

CH3OH (I)

Methanol (Methyl

alcohol)

The green plants make food by photosynthesis. During photosynthesis, carbon dioxide combines

with water in the presence of ‘sunlight’ and the green pigment of leaves called ‘chlorophyll’ to make

food like glucose and oxygen gas is given out.

6CO2 (g)

Carbon

dioxide

+ 6H2O (I)

Water

Sunlight

Chlorophyll

C6H12O6(aq)

Glucose

+ 6O2 (g)

Oxygen

TYPES OF CHEMICAL REACTIONS

i. Combination reactions,

ii. Decomposition reactions,

iii. Displacement reactions,

iv. Double displacement reactions, and

v. Oxidation and Reduction reactions.

COMBINATION REACTIONS

Those reactions in which two or more substances combine to form a single substance, are called

combination reactions.

In a combination reaction, two or more elements can combine to form a compound two or more

compounds can combine to form a new compound; or an element and a compound can combine to

form a new compound.

Magnesium and oxygen combine, when heated, to form magnesium oxide:

2Mg (s)

Magnesium

+ O2 (g)

Oxygen

combination 2MgO (s)

Magnesium oxide

(white)

Hydrogen burns in oxygen to form water:

2H2 (g)

Hydrogen

+ O2 (g) Combination 2H2O (I)

Water



Carbon (coal) burns in air to form carbon dioxide:

C (s)

Carbon (Coal)

+ O2 (g)

Oxygen

(From air)

Combination CO2 (g)

Carbon dioxide

Hydrogen combines with chlorine to form hydrogen chloride:

H2 (g)

Hydrogen

+ CI2 (g)

Chlorine

Combination 2HCI (g)

Hydrogen

chloride

(light green)

Sodium metal burns in chlorine to form sodium chloride:

2Na (s)

Sodium

+ CI2 (g)

Chlorine

Combination 2NaCI (s)

Sodium chloride

When iron powder is heated with sulphur, iron sulphide is formed:

Fe (s)

Iron

+ S (s)

Sulphur

Combination FeS(s)

Iron sulphide

(black)

Calcium oxide (lime or quicklime reacts vigorously with water to form calcium hydroxide (slaked

lime):

CaO (s)

Calcium oxide

(Lime or

Quicklime)

+ H2O (I)

Water

Combination

Ca(OH)2 (s)

Calcium hydroxide

(Slaked lime)

Test of carbon dioxide gas

When carbon dioxide reacts with lime water then lime water turns milky

Ca(OH)2 (aq)

Calcium hydroxide

(lime water)

+ CO2 (g)

Carbon dioxide

(From air)

CaCO3 (s) + H2O (I)

Ammonia reacts with hydrogen chloride to form ammonia chloride. This can be written as:

NH3 (g)

Ammonia

+ HCI (g)

Hydrogen chloride

Combination NH4CI (s)

Ammonium chloride

(white)

Carbon monoxide reacts with oxygen to from carbon dioxide:

2CO (g)

Carbon

monoxide

+ O2 (g)

Oxygen

Combination 2CO2 (g)

Carbon dioxide

Sulphur dioxide reacts with oxygen to produce sulphur trioxide. This reaction can be written as:

2SO2 (g)

Sulphur dioxide

+ O2 (g)

Oxygen

combination 2SO3

Sulphur trioxide



DECOMPOSITION REACTIONS

Those reactions in which a compound splits up into two or more simpler substances are known as

decomposition reactions.

The decomposition reactions are carried out by applying heat, light or electricity. Heat, light or

electricity provide energy which breaks a compound into two or more simpler compounds.

When calcium carbonate is heated, it decomposes to give calcium oxide and carbon dioxide:

CaCO3 (s)

Calcium carbonate

(Limestone)

Heat

Decompositon

CaO (s)

Calcium oxide

(Lime)

+ CO2 (g)

Carbon dioxide

When a decomposition reaction is carried out by heating, it is called ‘thermal decomposition’.

When potassium chlorate is heated in the presence of manganese dioxide catalyst (black colour), it

decomposes to give potassium chloride and oxygen:

2KCIO3 (s)

Potassium chlorate

Heat, MnO2

(Decomposition)

2KCI (s)

Potassium chloride

+ 3O2 (g)

Oxygen

When ferrous sulphate is heated strongly, it decomposes to from oxide, sulphur dioxide and sulphur

trioxide:

2FeSO4 (s)

Ferrous sulphate

(Green)

Heat

(Decomposition)

Fe2O3 (s)

Ferric Oxide

(Brown)

+ SO2 (g)

Sulphur

dioxide

+ SO3 (g)

Sulphur

trioxide

In this reaction, the green colour of ferrous sulphate changes to brown due to the formation of ferric

oxide. A smell of burning sulphur is obtained due to the formation of sulphur dioxide gas.

When lead nitrate is heated strongly, it breaks down to from simpler substances like head monoxide,

nitrogen and oxygen. This can be written as:

2Pb(NO3)2 (s)

Lead nitrate

(Colourless )

Heat

(Decomposition)

2PbO (s)

Lead monoxide

(Yellow)

+ 4NO2 (g)

Nitrogen dioxide

(Brown fumes)

+ O2 (g)

Oxygen

When electric current is passed through acidified water, it decomposes to give hydrogen gas and

oxygen gas. This reaction can be represented as:

2H2O (I)

Water

Electricity

(Decomposition)

2H2 (g)

Hydrogen

+ O2 (g)

Oxygen

The electrolysis of water produces 2 volumes of hydrogen gas and 1 volume of oxygen gas, we

conclude that the ratio of hydrogen and oxygen elements in water is 2:1 by volume.

When electric current is passed through molten sodium chloride, it decomposes to give sodium

metal and chlorine gas:

2NaCI (I)

Sodium chloride (Molten)

Electricity

(Decomposition)

2Na (s)

Sodium metal

+ CI2 (g)

Chlorine gas

This decomposition reaction is used to obtain sodium metal from sodium chlorine (common salt). It

is called electrolysis of molten sodium chloride.

When electric current is passed through molten aluminium oxide, it decomposes to give aluminium

metal and oxygen gas:

2Al2O3 (I)

Aluminium oxide (Molten)

Electricity

(Decomposition)

4Al (I)

Aluminium metal

+ 3O2 (g)

Oxygen gas



This decomposition reaction is used to extract aluminium metal from aluminium oxide. It is called

electrolysis of molten aluminium oxide.

When silver chloride is exposed to light, it decomposes to form silver metal and chlorine gas:

2AgCI (s)

Silver chloride

(White)

Light

(Decomposition)

2Ag (s)

Silver

(Greyish White)

+ CI2 (g)

Chlorine

(Yellowish – green)

In this reaction, the white colour of silver chloride changes to grayish white due to the formation of

silver metal. The decomposition of silver chloride is caused by light (It may by sunlight or bulb light).

This reaction is used in black and white photography.

Silver bromide also behaves in the same way as silver chloride with light energy.

2 AgBr (s)

Silver Bromide

(Pale yellow)

Light

(Decomposition)

2Ag (s)

Silver

(Greyish white)

+ Br2 (g)

Bromine

(Red – brown)

In this reaction, Pale yellow colour of silver bromide changes to grayish white due to the formation

of silver metal. The decomposition of silver bromide is caused by light. The light may be sunlight or

bulb light. This reaction of decomposition of silver bromide is also used in black and white

photography.

Uses of Decomposition Reactions:

The decomposition reactions carried by electricity are used to extract several; metals from their

naturally occurring compounds like chlorides or oxides. When the fused (molten) metal chloride or

metal oxide is decomposed by passing electricity, then metal is produced at the cathode (negative

electrode).

Decomposition Reactions in Our Body:

The digestion of food in the body is an example of decomposition reaction. When we eat foods like

wheat, rice, or potatoes, then the starch present in them decomposes to give simple sugars like

glucose in the body; and the proteins decompose to form amino acids.

DISPLACEMENT REACTIONS

Reactivity series of metals Reactivity series of non metals

Decreasing

reactivity of

Please

Send

Cat

Monkey

And

Potassium

Sodium

Calcium

Magnesium

Aluminium

K

Na

Ca

Mg

Al

F

C

B

I

Fluorine

Chlorine

Bromine

Iodine

F

Cl

Br

I



Zebra

In

Ten

Long

High

Cages

Make

Sure

Get

Padlocked

Zinc

Iron

Tin

Lead

Hydrogen

Copper

Mercury

Silver

Gold

Platinum

Zn

Fe

Sn

Pb

H

Cu

Hg

Ag

Au

Pt

metals

And non

metals

When a strip of zinc metal is placed in copper sulphate solution, then zinc sulphate solution and

copper are obtained:

CuSO4 (aq)

Copper sulphate

(Blue solution)

+ Zn (s)

Zinc

(Silvery – White)

ZnSO4 (aq)

Zinc Sulphate

(Colourless

solution)

+ Cu (s)

Copper

(Red – brown)

When a piece of magnesium metal is placed in copper sulphate solution, then magnesium sulphate

solution and copper metal are formed:

CuSO4 (aq)

Copper sulphate

(Blue solution)

+ Mg (s)

Magnesium

(Silvery white)

MgSO4 (aq)

Magnesium sulphate

(Colourless solution)

+ Cu (s)

Copper

(Red –

brown)

When a piece of iron metal (say, an iron nail) is placed in copper sulphate solution, then iron

sulphate solution and copper metal are formed:

CuSO4 (aq)

Copper sulphate

(Blue solution)

+ Fe (s)

Iron (Grey)

FeSO4 (aq)

Iron sulphate

Greenish solution)

+ Cu (s)

Copper

(Red – brown)

When a strip of lead metal is placed in a solution of copper chloride, then lead chloride solution and

copper metal are formed:

CuCI2 (aq)

Copper sulphate

(Green solution)

+ Pb (s)

Lead

(Blue Grey)

PbCI2 (aq)

Lead Chloride

(Colourless solution)

+ Cu (s)

Copper

(Red- brown)

When a copper strip is placed in a solution of silver nitrate, then copper nitrate solution and silver

metal are formed:

2AgNO3 (aq)

Silver nitrate

(Colourless

solution)

+ Cu (s)

Copper

(Red- brown)

CU(NO3)2 (aq)

Copper nitrate

(Blue solution)

+ 2Ag (s)

Silver

(grayish White)

Iron metal reacts with dilute hydrochloric acid to form iron (II) chloride and hydrogen gas:

Fe (s)

Iron

(As iron filings)

+ 2HCI (aq)

Hydrochloric

acid

FeCI2 (aq)

Iron (II) Chloride

(Ferrous chloride)

+ H2 (g)

Hydrogen



Magnesium metal reacts with hydrochloric acid to form magnesium chloride and hydrogen gas:

Mg (s)

Magnesium

+ 2HCI (aq)

Hydrochloric acid

MgCI2 (aq)

Magnesium

chloride

+ H2 (g)

Hydrogen

Sodium metal reacts with water to form sodium hydroxide solution and hydrogen gas:

2Na (s)

Sodium

+ 2H2O (I)

Water

2NaOH (aq)

Sodium hydroxide

+ H2 (g)

Hydrogen

Chlorine gas reacts with potassium iodide solution to form potassium chloride and iodine:

CI2 (g)

Chlorine

+ 2KI (aq)

Potassium iodide

2KCI (aq)

Potassium chloride

+ I2 (s)

Iodine

When copper oxide is heated with magnesium powder, then magnesium oxide and copper are

formed:

CuO (s)

Copper

oxide

+ Mg (s)

Magnesium

MgO (s)

Magnesium oxide

+ Cu (s)

Copper

When iron (III) oxide is heated with aluminium powder, then aluminium oxide iron metal are

formed:

Fe2O3 (s)

Iron (III) oxide

(Ferric oxide)

+ 2AI (s)

Aluminium

AI2O3 (s)

Aluminium oxide

+ 2Fe (I)

Iron (Molten)

DOUBLE DISPLACEMENT REACTIONS

Those reactions in which two compounds react by an exchange of ions to form two new compounds

are called double displacement reactions.

A double displacement reaction usually occurs in solution and one of the products, being insoluble,

precipitate out (separates as a solid).

When silver nitrate solution is added to sodium chloride solution, then a white precipitate of silver

chloride is formed along with sodium nitrate solution:

AgNO3 (aq)

Silver nitrate

+ NaCI (aq)

Sodium chloride

AgCI (s)

Silver chloride

(White ppt.)

+ NaNO3 (aq)

Sodium nitrate

When barium chloride solution is added to sodium sulphate solution, then a white precipitate of

barium sulphate is formed along with sodium chloride solution:

BaCI2 (aq)

Barium

chloride

+ Na2SO4 (aq)

Sodium sulphate

BaSO4 (s)

Barium sulphate

(White ppt.)

+ 2NaCI (aq)

Sodium chloride

Any reaction in which an insoluble solid (called precipitate) is formed that separates from the

solution is called a precipitation reaction.

If barium chloride solution is added to copper sulphate, then a white preceipitate barium sulphate is

produced along with copper chloride solution:

BaCI2 (aq)

Barium

+ CuSO4 (aq)

Copper

BaSO4 (s)

Barium sulphate

+ CuCI2 (aq)

Copper chloride



chloride sulphate (White ppt.)

When hydrogen sulphide gas is passed through copper sulpahte solution, then a black precipitate of

copper sulphide is formed along with sulphuric acid solution:

CuSO4 (aq)

Copper

sulphate

+ H2S (G)

Hydrogen sulphide

(rotten eggs smell)

CuS (s)

Copper

sulphide

+ H2SO4 (aq)

Sulphuric acid

When ammonium hydroxide solution is added to aluminium chloride solution, then a white

precipitate of aluminium hydroxide is formed along with ammonium chloride solution:

AICI3 (aq)

Aluminium

chloride

+ 3NH4OH (aq)

Ammonium

hydroxide

AI(OH)3 (s)

Aluminium hydroxide

(White ppt.)

+ 3NH4CI (aq)

Ammonium

chloride

When potassium iodide solution is added to lead nitrate solution, then a yellow precipitate of lead

iodide is produced along with potassium nitrate solution:

Pb(NO3)2 (aq)

Lead nitrate

+ 2KI

Potassium

iodide

PbI2(s)

Lead iodide

(yellow ppt.)

+ 2KNO3 (aq)

Potassium nitrate

The reactions between acids and bases to form salts and water are also double displacement

reactions. For example, sodium hydroxide and hydrochloric acid react to form sodium chloride and

water:

NaOH (aq)

Sodium

hydroxide

+ HCI (aq)

Hydrochloric acid

NaCI (aq)

Sodium

chloride

+ H2O (I)

Water

Ques 1. Write the balanced chemical equations for the following and identity the type of the reaction

in each case:

Barium

chloride (aq)

+ Potassium

sulphate (aq)

Barium Sulphate (s) + Potassium

Chloride (aq)

Zinc carbonate (s) Zinc oxide (s) + Carbon dioxide (g)

Hydrogen (g) + Chlorine (g) Hydrogen chloride (g)

Magnesium (s) + Hydrochloric acid (aq)

Magnesium

chloride (aq)

+ Hydrogen (g)

OXIDATION AND REDUCTION REACTIONS

The addition of oxygen to a substance is called oxidation.

The removal of hydrogen from a substance is also called oxidation.

The addition of hydrogen to a substance is called reduction.

The removal of oxygen from a substance is called reduction.

The process of reduction is just the opposite of oxidation.

Oxidation and reduction occur together.

The oxidation and reduction reactions are also called redox reactions.

When copper oxide is heated with hydrogen, then copper metal and water are formed:

CuO

Copper oxide

+ H2

Hydrogen

Heat Cu

Copper

+ H2O

Water



Substance oxidized: H2

Substance reduced: CuO

Oxidising agent: CuO

Reducing agent: H2

When hydrogen sulphide reacts with chlorine, then sulphur and hydrogen chloride are formed:

H2S

Hydrogen sulphide

+ CI2

Chlorine

S

Sulphur

+ 2HCI

Hydrogen chloride

Substance oxidized: H2S

Substance reduced: CI2

Oxidising agent: CI2

Reducing agent: H2S

The substance which gets oxidized is the reducing agent.

The substance which gets reduced is the oxidizing agent.

When zinc oxide is heated with carbon, then zinc metal and carbon monoxide are formed:

ZnO

Zinc oxide

+ C

Carbon

Heat Zn

Zinc

+ CO

Carbon monoxide

When manganese dioxide reacts with hydrochloric acid, then manganese dichloride, chlorine and

water are formed:

MnO2

Manganese

dioxide

+ 4HCI

Hydrochloric

acid

MnCI2

Manganese

dichloride

+ CI2

Chlorine

+ 2H2O

Water

There is another concept of oxidation and reduction in terms of metals and non – metals.

The addition of non – metallic element (or removal of metallic element) is called oxidation.

The addition of metallic element (or removal of non – metallic element) is called reduction.

When copper is heated in air, it reacts with the oxygen of air to form a black compound copper

oxide:

2Cu

Copper

(Red – brown)

+ O2

Oxygen

(From air)

Heat 2CuO

Copper oxide

(black)

CuO

Copper oxide

(Black)

+ H2

Hydrogen

Heat Cu

Copper

(Red – brown)

+ H2o

Water

Name the substances oxidized and substance reduced in the following reaction:

SO2

Sulphur

dioxide

+ 2H2S

Hydrogen

sulphide

2H2O

Water

+ 3S

Sulphur

Ques 2. Select the oxidising agent and the reducing agent from the following reaction:

H2S

Hydrogen

suphide

+ I2

Iodine

2HI

Hydogen

iodide

+ S

Sulphur

Ques 3. Identity the substance that is oxidised and the that is reduced in the following reaction:



4Na (s) + O2 (g) 2Na2O (s)

Ques 4. Which of the statement about the reaction below are incorrect?

2PbO (s) + C (s)

2Pb (s) + CO2 (g)

a) Lead is getting reduced.

b) Carbon dioxide is getting oxidised.

c) Carbon is getting oxidised.

d) Lead oxide is getting reduced.

Ques 5. A shiny brown coloured element X on heating in air becomes black in colour. Name the

element X and the black coloured compound formed.

EFFECTS OF OXIDATION REACTIONS IN EVERYDAY LIFE

There are two common effects of oxidation reactions which we observe in daily life. These are:

Corrosion of metals, and

Rancidity of food

Corrosion

Corrosion is the process in which metals are eaten up gradually by the action of air, moisture or a

chemical (such as an acid) on their surface.

Rusting of iron metal is the most common form of corrosion.

During the corrosion of iron (or rusting of iron), iron metal is oxidized by the oxygen of air in the

presence of water (moisture) to form hydrated iron (III) oxide called rust:

4Fe

Iron

+ 3O2

Oxygen

+ 2xH2O

Water

2Fe2O3.xH2O

Hydrated iron (III) oxide

(Rust)

The rusting of iron is a redox reaction. Rusting involves unwanted oxidation of iron metal which

occurs in nature on its own.

Copper reacts slowly with carbon dioxide and water vapour present in air and gets covered with a

green layer of basic copper carbonate (CuCO3.Cu(OH)2).

Silver (Ag) reacts very slowly with the hydrogen sulphide gas (H2S) present in air and gets covered

with a black coating of silver sulphide (AgS).

Corrosion weakens the iron and steel objects and structures such as railings, car bodies, bridges and

ships, etc and cuts short their life.

A lot of money has to be spent every year to prevent the corrosion of iron and steel objects, and to

replace the damaged iron and steel structures.

Rancidity

The condition produced by aerial oxidation of fats and oils in foods marked by unpleasant smell and

taste is called rancidity.

Rancidity spoils the food material prepared in fats and oils which have been kept for a considerable

time and makes them unfit for eating. The characteristics of a rancid food are that it gives out

unpleasant taste. Rancidity is called ‘Vikritgandhita’ in Hindi.



The development of rancidity of food can be prevented or retarded (slowed down) in the following

ways:

1) Rancidity can be prevented by adding anti – oxidants to foods containing fats and oils.

Anti – oxidant is a substance (or chemical) which prevents oxidation.

Anti – oxidants are actually reducing agents. When anti – oxidants are added to foods, then

the fats and oils present in them do not get oxidised easily and hence do not turn rancid. So

the foods remain good to eat for a much longer time.

Two common anti–oxidants used in foods to prevent the development of rancidity are BHA

(Butylated Hydroxy – Anisole) and BHT (Butylated Hydroxy – Toluene).

2) Rancidity can be prevented by packaging fat and oil containing foods in nitrogen gas.

When the packed food is surrounded by an unreactive gas nitrogen, there is no oxygen (of

air) to cause its oxidation and make it rancid. The manufacturers of patato chips (and other

similar food products) fill the plastic bags containing chips with nitrogen gas to prevent the

chips from being oxidised and turn rancid.

3) Rancidity can be retarded by keeping food in a refrigerator.

The refrigerator has a low temperature inside it. When the food is kept in a refrigerator, the

oxidation of fats and oils in it is slowed down due to low temperature. So, the development

of rancidity due to oxidation is retarded.

4) Rancidity can be retarded by storing food in air – tight containers.

When food is stored in air – tight containers, then there is little exposure to oxygen of air.

Due to reduced exposure to oxygen, the oxidation of fats and oils present in food is slowed

down and hence the development of rancidity is retarded.

5) Rancidity can be retarded by storing foods away form light.

In the absence of light, the oxidation of fats and oils present in food is slowed down and

hence the development of rancidity is retarded.

Assignment



QUESTION BANK FOR SUMMATIVE ASSESSMENT



1. Multiple choice Questions:

Choose the correct answer from the given options.

(i) Which of the following is a powerful reducing agent?

(a) Li (b) Cu (c) Au (d) Zn

(ii) Which of the following will liberate hydrogen from acids?

(a) Au (b) Cu (c) Ag (d)Na

(iii) When sodium is added to water it gets

(a) Reduced (b)hydrolysed (c) oxidised (d) none

(iv) When magnesium ribbon is burnt in air, the ash formed is

(a) Black (b) yellow (c) white (d) blue

(v) Oxygen gas

(a) Is colourless (c) support combustion

(b) Is odourless (d) all of them

(vi) In the electrolysis of water, oxygen is liberated at

(a) Cathode (b) anode (c) both cathode & anode (d) none of these

(vii) Which of the following is true about reduction?

(a) It involves addition of oxygen. (c) it involves removal of hydrogen.

(b) It involves gain of electron. (d) it involves loss of electron.

(viii) Rust is

(a) Hydrate ferrous oxide (c) only ferric oxide

(b) Only ferrous oxide (d) hydrate ferric oxide

(ix) Which of the following metal is protected by itself with a layer of its oxide?

(a) Silver (b) copper (c) gold (d) aluminium

(x) The term rancidity represents

(a) Acid rain (b) oxidation of fatty acids (c) rottening of fruits (d) fading of coloured

clothes

(xi) Which of the statements about the reaction below are incorrect?

2PbO(s) + C(s) → 2Pb(s) + CO2(g)

(p) leading is getting reduce (q) carbon dioxide is getting oxidized

(r) carbon is getting oxidized (s) lead oxide is getting reduced

(a) p and q (b) p and r (c) p, q and r (d) all of these

(xii) Fe2O3 + 2Al → Al2O3 + 2Fe

The above reaction is an example of a

(a) Combination reaction (c) decomposition reaction

(b) Double replacement reaction (d) displacement reaction

(xiii) What happens when dilute hydrochloric acid is added to iron filling?

(a) Hydrogen gas and iron chloride are produced.

(b) Chlorine gas and iron hydroxide are produced.

(c) No reaction takes place.

(d) Iron salt and water are produced.

2. Define the following:

(i) Chemical equation.

(ii) Combination reaction.

(iii) Decomposition reaction.



(iv) Displacement reaction.

(v) Double replacement reaction.

(vi) Oxidation.

(vii) Reduction.

(viii) Corrosion.

(ix) Rancidity.

3. Why does the colour of copper sulphate change when an iron nail is dipped in it?

4. How will you identify whether a chemical reaction is exothermic or endothermic in nature?

5. Which law of chemical combination of associated with the balancing of a chemical equation?

6. Why should a magnesium ribbon be cleaned before burning in air?

7. Why do we apply paint on iron articles? OR why are iron articles painted?

8. What does the term ‘aqueous’ represent?

9. Mention the role of oxidizing agent in a reaction?

10. What is rust?

11. What type of reaction is represented by the digestion of food in our body?

12. Write the balanced chemical equation for following statements: OR Translate the following statements

into chemical equations and then balance them:

(i) Solutions of barium chloride and sodium sulphate in water react ti give insoluble barium sulphate

and the solution of sodium chloride.

(ii) Hydrochloric acid solution react with sodium hydroxide solution to produce sodium chloride and

water.

(iii) Hydrogen reacts with chlorine to give hydrogen chloride.

(iv) Sodium metal reacts with water to produce sodium hydroxide and hydrogen.

(v) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitates of

barium sulphate.

(vi) Hydrogen combines with nitrogen to form ammonia.

(vii) Hydrogen sulphide gas burns in air to give water and sulphur dioxide.

(viii) Potassium metal reacts with water to gives potassium hydroxide and hydrogen gas.

(ix) Sodium hydroxide solution reacts with hydrochloric acid solution to produce sodium chloride

solution and water.

13. Balance the following chemical equations:

(i) HNO3 + Ca(OH)2 → Ca(NO3)2 +H2O

(ii) NaOH + H2SO4 → Na2SO4 + H2O

(iii) NaCl + AgNO3 → AgCl + NaNO3

(iv) BaCl2 + H2SO4 → BaSO4 + HCl

14. Write the balanced chemical equation fr the following reaction:

(i) Calcium hydroxide + carbon dioxide → calcium carbonate + water

(ii) Zinc + silver nitrate → zinc nitrate + silver

(iii) Aluminium + copper chloride → aluminium chloride + copper

(iv) Barium chloride + potassium sulphate → barium sulphate + potassium chloride

15. Write the balanced chemical equation for the following and identity the type of reaction in each case:

(i) Potassium bromide (aq) + barium iodide (aq) → potassium iodide (aq) + barium bromide (s)

(ii) Zinc carbonate (s) → zinc oxide (s) + carbon dioxide (g)

(iii) Hydrogen (g) + chlorine (g) → hydrogen chloride (g)

(iv) Magnesium (s) + hydrochloric acid (aq) → magnesium chloride (aq) + hydrogen (g)


(Answes the questions in about 30 words)



1. What happens when:

(i) An aqueous solution of silver nitrate is mixed with that of sodium chloride?

(ii) Hydrogen is burned in oxygen?

(iii) Carbon dioxide gas is bubbled through lime water in small quantity?

(iv) Aluminium reacts with sulphuric acid?

(v) Carbon dioxide gas is passed through lime water in excess?

2. Why are gold, silver and platinum considered as noble metals?

3. Why does the colour of copper sulphate solution change when a zinc rod is placed in it?

4. Why are food items preserved by flushing with nitrogen?

5. Why is respiration considered as an exothermic reaction?

6. During thermite welding the following reaction occurs:

Fe2O3 2Al → 2Fe + Al2O3

Find out the oxidizing and reducing agent stating why.

7. All decomposition reactions are endothermic reactions. Give reasom.

8. When lead nitrate solution and potassium iodide solution are mixed together, we get lead iodide and

potassium nitrate solutions. Write balanced chemical equation for the reaction involved.

9. A solution of substance ‘X’ is used for white-washing.

(i) Name the substance ‘X’ and write its formula.

(ii) Express the reaction of ‘X’ with water in the form of a balanced chemical equation.

10. Hydrogen burns in oxygen to give water. Explain the reaction on the basis of oxidation and reduction

reactions.

11. Identify the substances that are oxidized and the substance that are reduced in the following reactions:

(i) 4Na(s) + O2 → 2Na2O(s)

(ii) CuO(s) + H2 → Cu(s) + H2O(l)

12. What is balance chemical equation? Why should chemical equations be balanced?

13. Why are decomposition reactions called the opposite of combination reactions? Write equations for

these reactions.

14. Write one equation each for decomposition reactions where energy is supplied in the form of heat, light

or electricity.

15. In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper

metal. Write the reaction involved.

16. What do you mean by precipitation reaction? Explain by giving example.

17. Explain the following in terms of gain or loss of oxygen with two example each:

(i) Oxidation.

(ii) Reduction.

18. Oil and fat containing food items are flushed with nitrogen. Why?

19. Explain the following terms with one example each:

(i) Corrosion.

(ii) Rancidity.

20. Write the balanced chemical equation for the following reaction and identify the type of reaction and

define it.

“Iron (III) oxide reacts with aluminium and gives molten iron and aluminium oxide”.

21. Identify the type of chemical reaction and also write the chemical equation for the reaction that takes

place when a solution of potassium chloride is mixed with silver nitrate solution. Write the chemical

equation name of one the products obtained.

22. Write balanced chemical equations for the following reactions:

(i) Silver bromide on exposure to sunlight decomposes into silver and bromide.



(ii) Sodium metal reacts with water to form sodium hydroxide and hydrogen.

23. Write two observations that you will make when an iron nail in an aqueous solution of copper sulphate.

Write the chemical equation of this reaction.

24. Write the skeletal equations for the following reactions:

(i) Hydrogen sulphide reacts with sulphur dioxide to form sulphur and water.

(ii) Methane on burning combines with oxygen to produce carbon dioxide and water.

25. Barium chloride reacts with aluminium sulphate to give aluminium chloride and barium sulpahte.

(i) State the two types in which the above reaction can be classified.

(ii) Translate the above statement into a chemical equation.

26. Identify the type of reaction from the following equations:

(i) CH2 + 2O2 → CO2 + 2H2O

(ii) CaO + H2O → Ca(OH)2

(iii) Pb(NO3)2 + 2KI → PbI2 + 2KnO3

(iv) CuSO4 + Zn → ZnSO4 + Cu

27. Write balanced equation for the reaction between magnesium and hydrochloric acid. Name the product

obtained. Identify the type of reaction.

28. Translate the following statement into chemical equation and balance it.

“A metal in the form of ribbon burns with a dazzling white flame and changes into a white power.”

29. In attest tube, hydrochloric acid is poured over a few zinc granules. List two observation that suggest that

chemical reaction has occurred.

30. Write the chemical equation for the reaction between

(i) Al2O3 and HCl

(ii) Na2O and H2O

31. (i) state the law which is followed in balancing a chemical equation.

(ii) Balance the following chemical equation: Fe + H2O → Fe3O4 + H2.

32. Identify the type of reaction from the following equation and define it:

CH4 + 2O2 → CO2 + 2H2O + heat

33. List four observations that help us to determine whether a chemical reaction has taken place.

34. Consider the following chemical equation: Fe2O3 + 2Al → Al2O3 +2Fe

Name two categories in which you can place this reaction.

35. Name a compound that is used in black and white photography. Give a balanced chemical equation for

the reaction that takes place, when it is exposed to light. Also state the type of reaction.

36. Why do we need to balance a chemical equation?

37. Identify whether the following reactions are exothermic or endothermic:

(i) CaO + H2O → Ca(OH)2

(ii) CH4 +2O2 → CO2 + H2O

38. What happens when basic oxides like Na2O or K2O are dissolved in water? Write balanced chemical

equation.

39. Iron articles are shiny when new, but get coated with reddish-brown powder when left for sometimes.

Give reason.

40. Identify the type of each of the following reactions:

(i) A reaction in which a single product is formed from two or more reactants.

(ii) The reaction mixture becomes warm.

(iii) An insoluble substance is formed.

(iv) External surface of the container in which reaction takes place becomes freezing cold.





1. A small amount of calcium oxide or quick lime is placed in a beaker. Slowly some water is added. What do

you expect to happen in the situation? Refer to the diagram for help.

2. Explain the following with example:

(i) Precipitate (ii) Oxidation (iii) Reduction

3. A redox reaction is complementary in itself. Explain.

4. Give one example of decomposition reaction which is carried out by

(i) Electric energy (ii) Heat energy

5. (i) What are redox reactions.

(ii) Identify the substances oxidized and the substances reduced in the following reactions:

(a) 2PbO + c → Pb + CO2 (b) MnO2 + 4HCl → MnCl2 + 2H2O + Cl2

6. 2 g of ferrous sulphate crystals are heated in a boiling tube.

(i) State the colour of ferrous sulphate crystals both before heating and after heating.

(ii) Name the gases produced during heating.

(iii) Write the chemical equation for the reaction.

7. When the grapes are hanging on the plants, they do not ferment, but after being plucked from the plant,

they can ferment. What are the conditions for fermentation of the grapes?

8. Potato chips manufactures fill the packets of chips with a gas. Name the gas that is filled and state the

reasons for its filling.

9. Physical changes can be reserved but why can’t chemical changes be reserved?

10. What do you mean by electrolysis of acidulated water? What are the products obtained after the

electrolysis of water?

11. Write the balanced equation for the following chemical reactions:

(i) Hydrogen + chlorine → Hydrogen chloride

(ii) Barium chloride + Aluminium sulphate → barium sulphate +Aluminium hloride

(iii) Sodium + Water → Sodium hydroxide + Hydrogen

12. What does one mean by exothermic endothermic reactions? Give examples.

13. What is the difference between displacement and double displacement reactions? Write equations for

these reactions.

14. (i) Give an example for a combination reaction which is exothermic.

(ii) Identify the oxidizing agent and reducing agent in the following reaction:

H2S +Cl2 → 2HCl +S

15. What is rancidity? Mention any two ways by which rancidity can be prevented.

16. A small amount of quick lime is added to water in a beaker.

(i) Name and define the type of reaction that has taken place.

(ii) Write balanced chemical equation for the above reaction. Write the chemical name of the

product obtained.

(iii) State two observations that you will make in the reaction.

17. A metal M was placed in lead nitrate solution. After sometime, a thin layer of metal lead deposits on

metal M. which is more reactive – metal M or lead? Explain.

18. In the electrolysis of water,



(i) Name the gas collected at the cathode and anode respectively.

(ii) Why is the volume of one gas collected at one electrode double that at the other? Name this gas.

(iii) How will you test the evolved gases?

19. A metal ‘X’ acquires a green colour coating on its surface on exposure to air.

(i) Identify the metal ‘X’ and name the process responsible for this change.

(ii) Name and write chemical formula of the green coating formed on the metal.

(iii) List two important methods to prevent the process.

20. Write balance equations for the reaction of:

(i) Aluminium when heated in air. Write the name of the product.

(ii) Iron with steam. Name the product obtained.

(iii) Calcium with water. Why does calcium start floating in water.

21. A small amount of calcium oxide is taken in beaker and water is added slowly to it.

(i) Will there by any change in temperature of the contents? Explain.

(ii) Name and define the type of reaction taking place.

(iii) Write the chemical equation for the above reaction.

22. When is chemical reaction considered double displacement reaction? Explain giving example. State a

difference between displacement and double displacement reaction.

23. A brown substance ‘X’ on heating in air forms a substance ‘Y’. when hydrogen gas is passed over heated

‘Y’ it again changes back into ‘X’.

(i) Name the substance ‘X’ and ‘Y’.

(ii) Name the chemical processes occurring during both the changes.

(iii) Write the chemical equations involved in both the changes.

24. 2 g of lead nitrate powder is taken in a boiling tube. The boiling tube is heated over a flame. Now answer

the following questions:

(i) State the colour of fumes evolved and the residue left.

(ii) Name the type of chemical reaction that has taken place stating its balanced chemical equation.

25. State the meaning of oxidation in a chemical reaction. Consider the chemical reaction represented by the

following equation and write the names of the substances oxidized, reduced, oxidizing agent and reducing

agent in the reaction:

MnO2 + 4HCl → MnCl2 + 2H2O + Cl2

26. Write balanced equations for the following reactions:

(i) Dilute sulphuric acid reacts with aluminium powder.

(ii) Dilute hydrochloric acid reacts with sodium carbonate.

(iii) Carbon dioxide is passed through lime water.

27. A few crystals of copper sulphate are heated in a dry boiling tube.

(i) What is the colour of crystals before and after heating?

(ii) What is the reason for the colour change?

(iii) Can its original colour be restored? How?

28. Aqueous solutions of sodium sulphate and barium chloride react as follows:

Na2 + BaCl2 → BaSO4(s) + 2NaCl

(i) Identify the type of reaction.

(ii) Define the type of reaction.

(iii) Suggest the other name to this reaction.

29. Write balanced chemical equation for the reaction of dil. HCl with:

(i) Zn metal (ii) Na2CO3 (iii) NaOH



30. What is meant by skeletal chemical equation? What does it represent? Using the equation for electrolytic

decomposition of water, differentiate between the skeletal chemical equation and a balanced chemical

equation.

31. (i) state the meaning of reduction in terms of gain or loss of oxygen.

(ii) In the reaction represented by the following equatiom:

(a) Name the substance oxidized.

(b) Name the substance reduced.

(c) Name the oxidizing agent.

(d) Name the reducing agent.

32. The colour of freshly prepared solution of copper sulphate gradually changes when an iron nail is dipped

in it. Name the reaction that takes place. Define the reaction. Also give a balanced chemical equation

mentioning the state of the reactants and the products.

33. 2 g of lead nitrate powder is taken in a boiling tube. The boiling tube is heated over a flame. Now answer

the following questions:

(iii) State the colour of fumes evolved and the residue left.

(iv) Name the type of chemical reaction that has taken place stating its balanced chemical equation.

34. A metal compound ‘X’ reacts with dil. H2SO4 to produce effervescene. The gas evolved extinguishes a

burning candle. If one of the compounds formed is calcium sulphate, then what is ‘X’ and the gas

evolved? Also write a balanced chemical equation for the reaction which occurred.

35. A student has mixed the solution of lead (II) nitrate and potassium iodide.

(i) State the colour of the precipitate formed.

(ii) Write a balanced chemical equation for the reaction.

(iii) Suggest an alternative name for the above precipitation reaction. Give justification for your

answer.

36. An aqueous solution of metal nitrate reacts with sodium bromide solution to form yellow precipitate of

compound ‘Q’ which is used in photography. ‘Q’ on exposure to sunlight undergoes decomposition

reaction to form metal present along with a reddish- brown gas. Identify ‘P’ and ‘Q’.write balanced

chemical equation for the chemical reaction. List two categories in which this reaction can be placed.

IV. LONG ANSWER QUESTIONS (5 MARKS)


1. Marble and bronze statues often get corroded when kept in the open for a long time. Give reasons to

support this statement.

2. Given below is a figure showing an experiment. Identify the experiment. What does the experiment

show?

3. A housewife wanted her house to be white-washed, she bought 10 kg of quick lime from the market and

dissolved it in 30 litres of water. On adding quicklime to water, she noticed that the water started boiling

even when it was not heated. Give reason for her observation. Write the relevant equation and name the

product.



4. A student dropped a few pieces of marble in dilute hydrochloric acid present in beaker. The evolved gas

was collected and passed through lime water. What changes would be observed in lime water? What type

of reaction is it? Define it. Write the balanced chemical equation for both the changes observed.

5. With the help of a diagram show any displacement reaction.

6. On the basis of electron concept, show that the chemical reaction taking place between zinc and copper

sulphate dissolved in water is an example of a redox reaction.

7. Write balanced chemical equation for the reactions that take place during respiration. Identify the type of

combination reaction that takes place during this process and justify the name. give one more example of

this type of reaction.

8. (i) Identify the type of chemical reaction that will take place and define it. How will the colour of the salt

change?

(ii) Write the chemical equation of the reaction that takes place.

(iii) Mention one commercial use of this salt.

V. HOTS

1. A shiny brown-coloured element ‘X’ on heating in air becomes black colour. Name the element ‘X’ and the

black-coloured compound formed.

2. A student adds water to quicklime taken in a beaker. He feels the beaker turning hot. Why does this

happen? Write a chemical equation for the reaction. State the type of this reaction.

3. A solution of CuSO4 was kept in an iron pot. After a few days, the iron pot was found to have a number of

holes in it. Write the equations of the reaction that took place. Explain this reaction with Fe2O3. State the

special name given to this reaction.

VI. VALUE BASED QUESTIONS

1. When solid ammonium chloride (NH4Cl) is mixed with barium hydroxide octahydrate [Ba(OH)2.8H2O] in a

clean and dry test tube, a gas (X) is liberated and water droplets are deposited on the outer surface of the

test tube.

(i) Name the gas (X) liberated and write the balanced equation.

(ii) Gas X is also liberated by heating ammonium chloride with another base. Name that base.

(iii) Write the merit of one reaction over the other reaction in which gas X is liberated.

(iv) What is the cause of deposition of water droplets on the outer surface of the test tube in the

given reaction?

2. A student stores a blue solution of copper sulphate in a container made of zinc metal. After about half an

hour it was observed that the blue colour of the solution fades and the inner surface of the container is

spoiled.

(i) Why does the blue colour fade as time passes?

(ii) Why is the inner surface of the container spoiled?

(iii) What conclusions do you draw from the above two observations?

(iv) Which one is oxidized in the process?



(a) Zn (b) Cu (c) None

(v) Which one is reduced in the process?

(a) Zn (b) Cu (c) None

(vi) Write a balanced chemical equation for the process.

3. Quick lime is used for white-washing. When quick lime is dissolved in water slaked lime is formed which

gives a shining look to the surface of the wall when applied on it.

(i) Write the formula of quick lime.

(ii) What is the chemical name of slaked lime?

(iii) Give balanced chemical equation for the reaction between quick lime and water.

(iv) What is the cause of shining look of the surface of wall when slaked lime is applied on it?

(v) Write a balanced chemical equation when slaked lime react with carbon dioxide of the

atmospheric air.

4. Production of unpleasant taste and unpleasant smell in fatty and oily foods is called rancidity.

(i) Which process – oxidation or reduction is responsible for the rancidity of the fatty foods?

(ii) Name two factors which accelerate the rancidity.

(iii) Name two factors which slow down the rancidity.

One hundred and seventeen different chemical are known to us at present.

These combine to form a large number of compounds. On the basis of their chemical properties, all

the compounds can be classified into three groups:

Acids,

Bases, and

Acids, bases and salts



Salts

Colour indicators for Testing Acids and Bases

Define: An indicator is a ‘dye’ that changes its colour when it is put into an acid or a base.

How does an indicator tells us about acid and bases: An indicator tells us whether the substances

we are testing is an acid or a base by changing its colour.

The three most common indicators to test for acids and bases are: Litmus, Methyl orange and

phenolphthalein.

Litmus:-

Litmus is a natural indicator.

Colour: Litmus solution is a purple dye.

From where it is extracted: Litmus is extracted from a type of plant called ‘lichen’. Lichen is a

plant belonging to the division Thallophyta.

Nature of litmus: Litmus solution is neither acidic nor basic (it is neutral).

Color changes in acidic and basic solutions: It turns red in acidic solutions and blue in basic

solutions.

The most common indicator used for testing acids and bases in the laboratory is litmus.

In which form litmus is used: Litmus can be used in the form of litmus solution or in the form of

litmus paper. It is of two types: Blue litmus and Red litmus.

An acid turns blue litmus to red.

A basic (or alkali) turns red litmus to blue.

Methyl orange:

The neutral colour of methyl orange is ‘orange’.

Color changes in acidic and basic solutions: Methyl orange indicator gives red colour in acid

solution. Methyl orange indicator gives yellow colour in basic solution.

Phenolphthalein:

The neutral colour of phenolphthalein is ‘colourless’.

Color changes in acidic and basic solutions: Phenolphthalein indicator is colourless in acid

solution. Phenolphthalein indicator gives pink colour in basic solution.

Turmeric:

Turmeric is a neutral indicator.

Turmeric (haldi) contains a yellow dye.

It turns red in basic solutions. It remain yellow in acidic solutions.

The red cabbage extract:

The red cabbage extract (obtained from red cabbage leaves) is a neutral indicator.

It is red in colour. The red cabbage extract remains red in acidic solutions but turns green on

adding to basic solutions.

The coloured petals of Hydrangea, Petunia and Geranium flowers:

The coloured petals of some flowers (such as Hydrangea, Petunia and Geranium) which changes

colour in the presence of acids or bases also act as indicators.

The flower of Hydrangea plant is usually blue which turn pink in the presence of a base.



Why does the yellow stain of curry on cloth turns reddish brown and the colour vanishes off when the

cloth is rinsed with water?

A yellow stain of curry on a white cloth (which is due to the presence of turmeric in curry) turns

reddish- brown when soap solution is scrubbed on it. This is due to the fact that soap solution is

basic in nature which changes the colour of turmeric in the curry stain to red- brown. This stain turns

to yellow again when the cloth is rinsed with plenty of water. This is because then the basic soap

gets removed with water.

Olfactory Indicators

Those substances whose smell (or odour) changes in acidic or basic solutions are called olfactory

indicators. An olfactory indicator usually works on the principle when an acid or base is added to it,

then its ‘characteristic smell’ cannot be detected. Onion and Vanilla extract are olfactory indicators.

Onion has a characteristic smell. When a basic solution like sodium hydroxide solution is added to a

cloth strip treated with onions (or onion extract), then the onion smell cannot be detected. An acidic

solution like hydrochloric acid, however, does not destroy the smell of onions. This can be used as a

test for acids and bases.

Vanilla extract has a characteristic pleasant smell. If a basic solution like sodium hydroxide solution is

added to vanilla extract, then we cannot detect the characteristic smell of vanilla extract. An acidic

solution like hydrochloric acid, however, does not destroy the smell of vanilla extract. This can be

used as a test for acids and bases.

ACIDS

Acids are those chemical substances which have a sour taste. Acids change the colour of blue litmus

to red.

Raw mango, raw grapes, lemon, orange, and tamarind (imli), etc, are sour in taste due to the

presence of acids in them.

Soured milk (or curd) also contains lactic acid in it.

The acids present in plant materials and animals are called organic acids, Organic acids are naturally

occurring acids.

Acetic acid is found in vinegar (sirka), citric acid is present in citrus fruits such as lemons and oranges,

lactic acid is present in sour milk (or curd), tartaric acid is present in tamarind and unripe grapes,

oxalic acid is present in tomatoes whereas formic acid (or methanoic acid) is present in ant sting and

nettle leaf sting.

Organic acids (or naturally occurring acids) are weak acids. It is not harmful to eat or drink

substances containing naturally occurring acids in them.

The acids prepared from the minerals of the earth are called mineral acids. Mineral acids are man-

made acids.

The three most common mineral acids are: Hydrochloric acid, sulphuric acid and Nitric acid.

Concentrated mineral acids are very dangerous. They can burn our hands and clothes.

Concentrated and Dilute Acids

A concentrated acid is one which contains the minimum possible amount of water in it.

A dilute acid is one which contains much more of water in it.



Diluting of Acids is always done by mixing acid in water, not by mixing water in acid. Explain?

The process of mixing the concentrated acid with water is highly exothermic (or heat producing). So,

when a concentrated acid and water are mixed together, a large amount of heat is evolved.

The dilution of a concentrated acid is always be done by adding concentrated acid to water gradually

with stirring and not by adding water to concentrated acid. This is because: When a concentrated

acid is added to water for preparing a dilute acid, then the heat is evolved gradually, and easily

absorbed by the large amount of water (to which acid is being added).

If, however, water is added to concentrated acid to dilute it, then a large amount of heat is evolved

at once. This heat changes some of the water to steam explosively which can splash the acid on our

face or clothes and cause acid burns. Even the glass container may break due to excessive heating.

Properties of Acids

1. Acids have a sour taste

2. Acids turn litmus to red

3. Acid solutions conduct electricity (They are electrolytes)

4. Acids react with metals to from hydrogen gas

Metal + Acid Salt + Hydrogen gas

Most of the acids react with metals to form salts and evolve hydrogen gas.

Why curd, vinegar, lemon juice and orange juice should not be kept in metal vessels?

Curd and other sour foodstuffs such as vinegar, lemon juice and orange juice etc. should not be kept

in metal vessels (like copper vessels). This is because curd and other which can cause food poisoning

and damage our health.

5. Acids react with metal carbonates and metal hydrogen carbonates to form carbon dioxide gas and

water vapour.

Metal

carbonate

+ Acid Salt + Carbon dioxide + Water

Metal

hydrogen

carbonate

+ Acid Salt + Carbon dioxide + Water

Na2CO3 (s)

Sodium

carbonate

+ 2HCI (aq)

Hydrochloric

acid

2NaCI (aq)

Sodium

chloride

+ CO2

Carbon dioxide

(brisk

effervescence)

+ H2O

(I)

Water

Brisk effervescence (the rapid escape of small bubbles of gas from the liquid).

NaHCO3 (s)

Sodium

+ HCI

Hydrochloride NaCI (aq)

Sodium

+ CO2 (g)

Carbon dioxide

+ H2O

(I)

Zn (s)

Zinc

(A metal)

+ H2SO4 (aq)

Sulphuric acid

(Dilute)

ZnSO4 (aq)

Zinc sulphate

(A salt)

+ H2 (g)

Hydrogen



hydrogen

carbonate

acid chloride Water

Tests of carbon dioxide

Carbon dioxide gas does not support combustion. So, carbon dioxide gas can extinguish a burning

substance (say, a burning candle).

When carbon dioxide gas is passed through lime water, the lime water turns milky due to the

formation of a white precipitate of calcium carbonate:

Ca(OH)2 (aq)

Calcium hydroxide

(Lime water)

+ CO2 (g)

Carbon

dioxide

CaCO3 (s)

Calcium carbonate

(White ppt.)

+ H2O (I)

Water

What happens if excess of carbon dioxide is passed through lime water?

If excess of carbon dioxide gas is passed through lime water, then the white precipitate formed first

dissolves due to the formation of a soluble salt calcium hydrogen carbonate, and the solution becomes

clear again:

CaCO3 (s)

Calcium carbonate

(White ppt.)

(Insoluble in water)

+ CO2 (g)

Carbon

dioxide

+ H2O (I)

Water

Ca(HCO3)2 (aq) Calcium

hydrogen carbonate

(soluble in water)

What should we suggest to a person suffering from acidity?

If someone is suffering from the problem of acidity after overeating, we can suggest taking baking

soda solution as remedy. This is because baking soda is sodium hydrogen carbonate which reacts

with excess hydrochloric acid in the stomach and neutralises it. This gives relief to the person

suffering from acidity.

What are the other forms of calcium carbonate? What happens when calcium carbonate reacts with

dilute hydrochloric acid and dilute sulphuric acid?

Limestone, marble and chalk are the different forms of the same chemical compound ‘calcium

carbonate’. Even the egg-shells are made of calcium carbonate.

Calcium carbonate reacts with dilute hydrochloric acid to form calcium chloride, carbon dioxide and

water.

Calcium carbonate reacts with dilute sulphuric acid to form calcium sulphate, carbon dioxide and

water.

6. Acids react with bases (or alkalis) to form salt and water

Acid + Base Salt + Water

The reaction between an acid and a base to form salt and water is called a neutralization reaction.

NaOH (aq)

Sodium hydroxide

(Base)

+ HCI (aq)

Hydrochloric acid

(Acid)

NaCI (aq)

Sodium chloride

(Salt)

+ H2O (I)

Water

7. Acids react with metal oxides to form salt and water

Metal oxide + Acid Salt + Water



8. The acids also react with metal hydroxides to form salt and water. The reaction between an acid and

a metal hydroxide is also a kind of neutralisation reaction.

What is used to treat the acidity in stomach? How does it treat it?

The antacid called ‘Milk of Magnesia’ which is used to remove indigestion (caused by too much

hydrochloric acid in the stomach) is a metal hydroxide called ‘magnesium hydroxide’. Magnesium

hydroxide is basic in nature. It reacts with the excess hydrochloric acid present in the stomach and

neutralises it.

9. Acids have corrosive nature

The mineral acids cause severe burns on the skin and attack and eat up materials like cloth, wood,

metal, structures and stonework, so they are said to be corrosive. For example, if concentrated

sulphuric acid falls accidently on skin, clothes or wood, it causes severe burns on the skin, it cuts

holes in the clothes, and burns the wood producing black spots on its surface.

Why acids are not stored in metal containers? In which type of containers acids are stored and why?

Acids are never stored in metal containers because they gradually corrode and eat up the metal

container. Acids are stored in containers made of glass and ceramics because they are not attacked

by acids.

What do all acids have in common

An acid is a substance which is dissociates (or ionizes) on dissolving in water to produce hydrogen

ions [H+(aq) ions].

HCI (aq)

Hydrochloric acid H+ (aq)

Hydrogen ions

+ CI- (aq)

Chloride ions

It is the presence of hydrogen ions [H+ (aq) ions] in hydrochloride acid solution which makes it

behave like an acid.

Hydrogen ions do not exist as H+ ions in solution, they attach themselves to the polar water

molecules to form hydronium ions, H3O+.

H+

Hydrogen ion

+ H2O

Water

H3O+

Hydronium ion

H+ (aq) and H3O+ are just the same because: H+ + H2O.

A common thing in all the acids is that they produce hydrogen ions [H+ (aq) ions] when dissolved in

water. Thus, the acidic behavior of an acid solution is due to the presence of hydrogen ions in it.

HCI (aq) H+ (aq) + CI- (aq)

H2SO4 (aq) 2H+ (aq) + SO42- (aq)

HNO3 (aq) H+ (aq) + NO3- (aq)

CH3COOH (aq) CH3COO- (aq) + H+ (aq)

CuO (s)

Coppper (II)

oxide

(Black)

+ 2HCI (aq)

Hydrochloric acid

CuCI2 (aq)

Copper (II)

chloride

(Blue- green)

+ H2O (l)

Water



Why compounds containing hydrogen such as glucose (C6H12O6) and alcohol (C2H5OH) do not show

acidic character?

The compounds such as glucose (C6H12O6) and alcohol (C2H5OH) also contain hydrogen but they do

not show acidic character. The aqueous solutions of glucose and alcohol do not show acidic

character because their hydrogen does not separate out as hydrogen ions [H+(aq) ions] on dissolving

in water.

Why acids conduct electricity? But glucose and alcohol do not conduct electricity?

The aqueous solution of an acid conducts electricity due to the presence of charged particles called

ions in it. For example, when hydrochloric acid (HCI) is dissolved in water, then its solution contains

hydrogen ions, H+ (aq) and chloride ions, CI- (aq). These ions can carry electric current. So, due to the

presence of H+ (aq) ions and CI- (aq) ions, a solution of hydrochloric acid conducts electricity.

The hydrogen containing compounds like glucose and alcohol do not produce hydrogen ions or some

other ions in solution. So, due to the absence of ions, glucose solution and alcohol solution do not

conduct electricity.

Why distilled water does not conduct electricity? Why rain water conduct electricity?

Distilled water does not conduct electricity because it does not contain any ionic compound (like

acids, bases or salts) dissolved in it. On the other hand, rain water conducts electricity.

Rain water, while falling to the earth through the atmosphere, dissolves an acidic gas carbon dioxide

from the air and forms carbonic acid (H2CO3). Carbonic acid provides hydrogen ions, H+ (aq), and

carbonate ions, CO32- (aq) to rain water. So, due to the presence of carbonic acid (which provides

ions to rain water), the rain water conducts electricity.

Why Acids Do Not Show Acidic Behaviour in the Absence of Water?

The acids do not produce hydrogen ions in the absence of water and hence will not show its acidic

behaviour.

Why dry HCL gas does not show acidic behaviour in the absence of water?

Dry HCL gas does not contain any hydrogen ions in it, so it does not show acidic behaviour. In fact,

dry HCI gas does not change the colour of dry blue litmus paper because it has no hydrogen ions

[H+(aq) ions] in it. However, when HCI gas dissolves in water, it forms hydrogen ions and hence

shows acidic behaviour:

HCI (g) Dissolve in water

H+ (aq) + CI- (aq)

The separation of H+ ions from HCI molecules cannot occur in the absence of water. The separation

of H+ ions from HCI molecules can occur only in the presence of water. That is why HCI gas shows

behaviour only in the presence of water.

Why HCL gas turns wt blue litmus paper red?

The HCL gas turns ‘wet’ blue litmus paper red because it dissolves in the water present in wet litmus

paper to form hydrogen ions, H+ (aq) ions, which can turn blue litmus paper to red.

HCL + H2O H3O+

Hydronium ion

+ CI-



Strong Acids

An acid which is completely ionized in water and thus produces a large amount of hydrogen ions is

called a strong acid.

For example, hydrochloric acid is completely ionized in water, so it is a strong acid.

HCL (aq) H+ (aq) + CI- (aq)

The single arrow pointing towards right in the above equation indicates that hydrochloric acid is

completely ionized to form ions.

Sulphuric acid (H2SO4) and nitric acid (HNO3) are also strong acids because they are fully ionized in

water to produce a large amount of hydrogen ions.

The word ‘strong’ here refers to the ‘degree of ionisation’ and not to the ‘concentration’ of the acid.

Due to large amount of hydrogen ions in their solution, strong acids react very rapidly with other

substances (such as metals, metal carbonates and metal hydro carbonates, etc). Strong acids also

have a high electrical conductivity because of the high concentration of hydrogen ions in their

solution.

Weak Acids

An acid which is partially ionized in water and thus produces a small amount of hydrogen ions is

called a weak acid. Example, acetic acid is partially ionized in water to produce only a small amount

of hydrogen ions, so it as a weak acid:

CH3COOH (aq)

Acetic acid

CH3COO- (aq)

Acetate ions

+ H+ (aq)

Hydrogen ions

The double arrow pointing towards right as well as left in the above equation tells acetic acid does

not ionize fully to form hydrogen ions. Carbonic acid (H2CO3) are also weak acids because they ionize

only partially in water to form a small amount of hydrogen ions. Due to a small amount of hydrogen

ions present in their solution, weak acids react quite slowly with other substances (such as metals,

metal carbonates and metal hydrogen carbonates, etc,) Weak acids have low electrical conductivity

because of the low concentration of hydrogen ions in them.

When the concentrated solution of an acid is diluted by mixing water, then the concentration of

hydrogen ions H+ (aq) [or hydronium ions, H3O+] per unit volume decreases.

Uses of Mineral Acids in Industry

Sulphuric acid is used in the manufacture of fertilizers (like ammonium sulphate), paints, dyes,

chemicals, plastics, synthetic fibres, detergents, explosives and car batteries.

Nitric acid is used for making fertilizers (like ammonium nitrate), explosive (like TNT: Tri-nitro

Toluene), dyes and plastics.

Hydrochloric acid is used for removing oxide film steel objects (before they are galvanized) and for

removing ‘scale’ deposits from inside the boilers. It is also used in dye-stuffs, textile, food and

leather industries.

BASES



Bases are those chemical substances which have a bitter taste. All the base change the colour of red

litmus to blue.

A base is a chemical substance which can neutralize an acid. All the metal oxides and metal

hydroxide are bases.

For example, sodium oxide (Na2O) is sodium hydroxide (NaOH), calcium oxide (or lime) (CaO),

calcium hydroxide (or slaked lime) [Ca(OH)2], Ammonium hydroxide (NH4OH).

Metal carbonates and metal hydrogen carbonate are also considered to be bases because they

neutralize the acids. Thus, sodium carbonate (Na2CO3), calcium carbonate (CaCO3) and sodium

hydrogen carbonate (NaHCO3) are also bases.

Water Soluble Bases: Alkalis

A base which is soluble in water an alkali. Sodium hydroxide (NaOH), Potassium hydroxide (KOH),

Calcium hydroxide [Ca(OH2], Ammonium hydroxide (NH4OH), and Magnesium hydroxide [Mg(OH)2].

The soluble bases (or alkali) are much more useful than insoluble bases because most of the

chemical reactions take place only in aqueous solutions (or water solutions).

What Do All the Bases Have in Common

A base is a substance which dissolve in water to produce ions (OH- ions) in solution.

NaOH (s)

Sodium hydroxide

(Base or Alkali)

Water

Na+ (aq)

Sodium ions

+ OH- (aq)

Hydroxide

ions

KOH (s) Water

K+ (aq) + OH- (aq)

Mg(OH)2 (s) Water

Mg2+ (aq) + 2OH- (aq)

A common property of all the bases (or alkalis) is that they all produce hydroxide ions (OH- ions)

when dissolved in water. NaOH, KOH, Mg(OH)2, Ca(OH)2 and NH4OH are all bases (or alkalis) because

they dissolve in water to produce hydroxide ions (OH- ions).

Bases are of two types: strong bases and weak bases.

Strong Bases

A base which completely ionizes in water and thus produces a large amount of hydroxide ions (OH-

ions) is called a strong base (or a strong alkali).

Sodium hydroxide (NaOH) and potassium hydroxide (KOH) are strong bases (or strong alkalis). This is

because they completely ionize on dissolving in water to produce a large amount of hydroxide ions

(OH- ions).

Weak Bases

A base which is partially ionized in water and thus produces a small amount of hydroxide ions (OH-

ions) is called a weak base (or weak alkali).

Ammonium hydroxide (NH4OH), Calcium hydroxide [Ca(OH)2] and magnesium hydroxide [Mg(OH)2]

are weak bases (or weak alkalis). This is because they ionize only partially on dissolving in water and

produce a small amount of hydroxide ions (OH- ions).



Properties of Bases

1) Bases have bitter taste

2) Bases feel soapy to touch

3) Bases turn red litmus to blue

4) Bases conduct electricity in solution (They are electrolytes)

5) Bases react with some metals to form hydrogen gas.

2NaOH (aq)

Sodium

hydroxide

(Base)

+ Zn (s)

Zinc

Heat

Na2ZnO2 (aq)

Sodium Zincate

(Salt)

+ H2 (g)

Hydrogen

6) Bases react with acids to form salt and water

2NaOH (aq)

Sodium

hydroxide

(Base)

+ H2SO4 (aq)

Sulphuric acid

(Acid)

Na2SO4 (aq)

Sodium sulphate

(Salt)

+ 2H2O (I)

Water

What happens when an acid and a base combines?

When an acid and a base combine then the real neutralization reaction occurs due to the

combination of hydrogen ions present in acid and hydroxide ions present in base to form water.

H+ (aq)

Hydrogen ions

(From acid)

+ OH- (aq)

Hydroxide ions

(From base)

Neutralisation

reaction

H2O (I)

Water

7) Bases react with non-metal oxides to form salt and water

Non-metal

oxide

+ Base Salt + Water

Ca(OH)2 (aq)

Calcium

hydroxide

(Base)

+ CO2 (g)

Carbon dioxide

(Non-metal oxide)

CaCO3 (s)

Calcium

carbonate

(Salt)

+ H2O (I)

Water

Uses of Bases

Sodium hydroxide is used in the manufacture of soap, paper and a synthetic fibre called ‘rayon’.

Calcium hydroxide (called slaked lime) is used in the manufacture of bleaching powder.

Magnesium hydroxide is used as an ‘antacid’ to neutralize excess acid in the stomach and cure

indigestion.

Sodium carbonate is used as washing soda and for softening hard water.

Sodium hydrogen carbonate is used as baking soda in cooking food, for making baking powders, as

an antacid to cure indigestion and in soda-acid fire extinguishers.

STRENGTH OF ACID AND BASE SOLUTIONS: pH SCALE

Why water is neutral?



Water (H2O) is slightly ionized into hydrogen ions (H+) and hydroxide ions (OH-). In pure water, the

concentration of hydrogen ions and hydroxide ions are equal. Due to this, pure water is neither

acidic nor basic, it is neutral.

What happens to the hydrogen ion concentration when acid is added to water?

Acids produce hydrogen ions in water. So, when an acid is added to water, then the concentration of

hydrogen in water increases. The solution of acid thus formed will have more of hydrogen ions (and

less of hydroxide ions), and it will be acidic in nature. In other words, acidic solutions have excess of

hydrogen ions.

Acids also contain hydroxide ions

Even the acidic solutions contain hydroxide ions which come from the ionization of water but the

concentration of hydroxide ions in acidic solutions is much less than that of hydrogen ions.

What happens to the hydroxide ion concentration when base is added to water?

Bases produce hydroxide ions in water. So, when a base is added to water, then the concentration of

hydroxide ions in it increases. The solution formed by dissolving a base in water will have more of

hydroxide ions (and less of hydrogen ions), and it will be basic in nature, In other words, the basic

solutions have excess of hydroxide ions.

Bases also contain hydrogen ions

Even the basic solutions have hydrogen ions in them which come from the ionization of water but the

concentration of hydrogen ions in basic solutions is much less than that of hydroxide ions.

pH scale

In 1909 Sorenson devised a scale (known as pH scale) on which the strength of acid solutions as well

as basic solutions could be represented by making use of the hydrogen ion concentration in them.

Sorenson linked the hydrogen ion concentrations of acd and base solutions to the simple numbers 0

to 14 on his pH scale.

The pH of a solution is inversely proportional to the concentration of hydrogen ions in it. That is, a

solution having a high concentration of hydrogen ions has a low pH value. On the other hand, a

solution having low concentration of hydrogen ions has a high pH value.

In the term pH, letter ‘p’ stands for a German word ‘Potenz’ which means ‘Powder’ and letter H

stands for hydrogen ions concentration [H+].

The strength of an acid or base is measured on a scale of numbers called the pH scale. The pH scale

has values from 0 to 14.

pH is a pure number, it has no units.

The rules of pH scale.

Neutral substances have a pH of exactly 7.

Acids (or acidic solutions) have a pH of less than 7.

Lower the pH, the stronger the acid.

Bases (or basic solutions) have a pH of more than 7.

The higher the pH, the stronger the base (or alkali).



Universal Indicator

Universal indicator is a mixture of many different indicators (or dyes) which gives different colours at

different pH values of the entire pH scale.

How does a universal indicator works?

The universal indicator shows different colours at different concentrations of hydrogen ions in the

solution.

When an acid or base solution is added to the universal indicator, the indicator produces a new

colour. The colour produced by universal indicator is used to find the pH value of the acid or base

solution by matching the colour with the colours on pH colour chart. And knowing the pH value, we

can make out whether the given solution is a strong acid, weak acid, strong base or a weak base.

pH Colour pH Colour pH Colour

0 Dark red 5 Orange yellow 10 Navy blue

1 Red 6 Greenish yellow 11 Purple

2 Red 7 Green 12 Dark purple

3 Orange red 8 Greenish blue 13 Violet

4 Orange 9 Blue 14 Violet

IMPORTANCE OF pH IN EVERYDAY LIFE

pH in Our Digestive System

Importance: Our stomach produces hydrochloric acid (of pH about 1.4). This dilute hydrochloric acid

helps in digesting our food without harming the stomach.

How acidity or indigestion is caused: Excess of acid is produced in the stomach due to various

reasons (one being overeating). The excess acid in the stomach causes indigestion which produces

pain and irritation.

How to cure indigestion or acidity caused in stomach: In order to cure indigestion and get rid of

pain, we can take bases called ‘antacids’ (antacid’ means ‘anti-acid’ ). Antacids are group of mild

bases which have no toxic effects on the body. Being basic in nature, antacids react with excess acid

in the stomach and neutralize it. This gives relief to the person concerned.

Example of antacids: The two common antacids used for curing indigestion due to acidity are:

Magnesium hydroxide (Milk of Magnesia) and sodium hydrogen carbonate (Baking soda).

pH Changes as the cause of Tooth Decay

Cause: When we eat food containing sugar, then the bacteria present in our mouth break down the

sugar to form acids (such as lactic acid). Thus, acid is formed in the mouth after a sugary food has

been eaten. This acid lowers the pH in the mouth (making it acidic) Tooth decay starts the pH of acid

formed in the mouth falls below 5.5. This is because then the acid becomes strong enough to attack

the enamel of our teeth and corrode it. This sets in tooth decay. Through tooth enamel is made of

calcium phosphate (which is the hardest material in our body), but it starts getting corroded when

the pH in the mouth is lower than 5.5.

Prevention of tooth decay: The best way to prevent tooth decay is to clean the mouth thoroughly

after eating food (by rinsing it with lots of clean water). Many toothpastes contain bases to



neutralize the mouth acid (the pH of toothpaste being about 8.0). So, using the toothpastes (which

are basic) for cleaning the teeth can neutralize the excess acid in mouth and prevent tooth decay.

Reduction of chances of tooth decay: A person can lessen the chances of suffering from tooth decay

by changing his eating habits such as eating less of sugary foods like sweets, toffees, ice-cream,

chocolates, and candy, etc.

pH Changes and Survival of plants

Soil pH and Plant Growth: Most of the plants grow best when the pH of the soil is close to 7. If soil is

too acidic or too basic (too alkaline), then the plant grow badly or do nor grow at all.

How the pH of soil is affected: The soil may be acidic or basic naturally. The soil pH is also affected

by the use of chemical fertilizers in the fields. The pH of acidic soil can reach as low as 4 and that of

the basic soil can go up to 8.3.

What can be added to soil if the soil is too acidic: If the soil is too acidic (having low pH), then it is

treated with materials like quicklime (calcium oxide) or slaked lime (calcium hydroxide) or chalk

(calcium carbonate). All these materials are bases and hence react with the excess acid present in

soil and reduce its acidity. A farmer should add lime (or slaked lime or chalk) in his field when the soil

is too acidic.

What can be added to soil if the soil is too acidic: If the soil is too alkaline then its alkalinity can be

reduced by adding decaying organic matter manure or compost) which contains acidic materials.

pH Changes and Survival of Animals

How is our body affected due to the change of pH: The pH plays an important role in the survival of

animals, including human beings. Our body works well within a narrow pH range of 7.0 to 7.8. If, due

to some reason, this pH range gets disturbed in the body of a person, then many aliments can occur.

How is aquatic life affected due to the change of pH: The aquatic animals (like fish) can survive in

lake or river water within a narrow range of pH change. When the pH of rain water is about 5.6, it is

called acid rain. Too much acid rain can lower the pH of lake water or river water to such an extent

(and make it so acidic) that the survival of aquatic animals becomes difficult. The high acidity of lake

water or river water can even kill the aquatic animals (like fish).

How the pH of river can be adjusted if river water is acidic: Calcium carbonate is often added to

acidic lake water to neutralize the acid that comes from acid rain. This prevents the fish in the lake

from being killed.

Self Defence By Animals and Plants through Chemical Warfare

Honey bee:

What happens when a honey bee stings: When a honey-bee stings a person, it injects an acidic

liquid into the skin which causes immense pain and irritation.

How can we get relief if honey bee stings: If the bee stings a person, then rubbing a mild base

like baking soda solution on the stung area of the skin gives relief. This is because, being a base,

baking soda neutralise the acidic liquid injected by bee sting and cancels its effect.

Wasp sting:

What happens when a wasp stings: When a wasp stings, it injects an alkaline liquid into the skin,

which causes immense pain and irritation.



How can we get relief if wasp stings: If a wasp stings a person, then rubbing a mild acid like

vinegar on the stung area of the skin gives relief. This is because, being an acidic substance,

vinegar neutralises the alkaline liquid by the wasp sting and cancels its effect.

Ant:

What happens when an ant stings: An ant’s sting injects methanoic acid into the skin of a person

causing burning pain.

How can we get relief if ant stings: An ant’s sting injects methanoic acid into the skin of a

person, being acidic, an ant’s sting can be neutralised by rubbing a mild base like baking soda on

the affected area of the skin.

Nettle plant: (Nettle is a wild herbaceous plant found in the jungles.)

What happens when we accidentally touches nettle leaves: The nettle leaves have stinging hairs.

When a person happens to touch the leaves of a nettle plant accidently, the stinging hair of nettle

leaves inject methanoic acid into the skin of the person causing burning pain.

How can we get relief if we accidentally touch nettle leaves: The stinging hair of nettle leaves inject

methanoic acid into the skin of the person, the nettle sting, being acidic, can be neutralised by

rubbing baking soda on the skin.

Natural remedy of nettle leaves stings: Nature itself has provided remedy for the nettle stings in the

form of a ‘dock’ plant. So, a traditional remedy for the nettle leaf sting is to rub the stung area of the

skin of the person with the leaf of a dock plant (which often grows beside the nettle plant in the

jungle).

SALTS

A salt is a compound formed from an acid by the replacement of the hydrogen in the acid by a

metal.

Hydrochloric acid is HCI. If we replace the hydrogen (H) of this acid by a metal atom, say a sodium atom

(Na), then we will get a salt NaCI. This is called sodium chloride.The hydrogen of acid is replaced by an

ammonium group (NH4) as in the case of ammonium chloride, NH4CI.

Salts are formed when acids react with bases.

The salts of ‘hydrochloric acid’ are called ‘chlorides’.

The salts of ‘sulphuric acid’ are called ‘sulphates’.

The salts of ‘nitric acid’ are called ‘nitrates’.

The salts of ‘carbonic acid’ are called ‘carbonates’.

The salts of ‘acetic acid’ are called ‘acetates’.

Just like acids and bases, solution of salts in water conduct electricity. That is, salts are electrolytes.

Salt solution conducts electricity due to the presence of ions in them. Salts are ionic compounds.

Every salt consists of a positively charged ion (cation) and a negatively charged ion (called anion).

Family of Salts

The salts having the same positive ions (or same negative ions) are said to belong to a family of salts.

The pH of Salt Solutions

Through the aqueous solutions of many salts are neutral (having a pH of 7), but some salts produce

acidic or basic solutions (alkaline solutions) when dissolved in water.



The acidic nature and basic nature of some salt solutions can be explained on the basic of hydrolysis

of salts.

The salts of strong acids and strong bases give neutral solutions.

Sodium chloride salt (NaCI) is formed from a strong acid hydrochloric acid (HCI), and a strong base

sodium hydroxide (NaOH).

The salts of strong acids and weak bases gives acidic bases give acidic solution.

Ammonium chloride (NH4CI) is the slat of a strong acid hydrochloric acid (HCI), and a weak base

ammonium hydroxide (NH4OH), so an aqueous solution of ammonium chloride is acidic in nature.

NH4CI (s)

Ammonium

chloride

+ H2O (I)

Water

Hydrolysis

NH4OH (aq)

Ammonium hydroxide

(Weak base)

+ HCI (aq)

Hydrochloric acid

(Strong acid)

Hydrochloric acid is a strong acid which is fully ionised and gives a large amount of hydrogen ions

[H+(aq)]. On the other hand, ammonium hydroxide is a weak base which is only slightly ionised and gives

a small amount of hydroxide ions [OH-(aq)]. Since ammonium chloride solution contains more of

hydrogen ions than hydroxide ions, it is acidic nature. It turns blue litmus red.

Another example of a salt which gives an acidic solution is ammoinium sulpahte (NH4)2SO4.

The salts of weak acids and strong bases give basic solutions (or alkaline solutions).

Sodium carbonate (Na2CO3) is the salt of a weak acid carbonic acid (H2CO3) and a strong base sodium

hydroxide (NaOH), so an aqueous solution of sodium carbonate will be basic in nature.

Na2CO3 (s)

Sodium

carbonate

+ 2H2O (I)

Water

Hydrolysis

2NaOH (aq)

Sodium hydroxide

(Strong base)

+ H2CO3 (aq)

Carbonic acid

(Weak acid)

Another example of a salt which gives a basic solution is sodium acetate (Ch3COONa).

COMMON SALT (SODIUM CHLORIDE)

The common salt is a white powder which in preparing food, especially vegetables and pulses, etc.

Common salt is also known as just ‘salt’. The chemical name of common salt is sodium chloride

(NaCI). Common salt (or sodium chloride) is a neutral salt.

Sodium chloride can be made in the laboratory by

NaOH (aq)

Sodium

hydroxide

+ HCI (aq)

Hydrochloric acid

NaCI (aq)

Sodium chloride

(Common salt)

+ H2O (I)

Water

From where Common Salt is Obtained

Common Salt from Sea-Water: Sea-water contains may dissolved salts in it. The major salt present

in sea- water is common salt (or sodium chloride). Common salt is obtained from sea-water by the

process of evaporation.

How common salt is obtained from sea-water: This is done as follows: Sea-water is trapped in large,

shallow pools and allowed to stand there. The sun’s heat evaporates the water slowly and common



salt is impure because it has some other salts missed in it. It is purified to obtain pure common salt

(or sodium chloride). The huge quantities of common salt required by industry come from sea-water.

Common salt from Underground Deposits: Underground deposits of common salt are found in

many parts of the world. The large crystals of common salt found in underground deposits are called

rock salt. Rock salt is usually brown due to the presence of impurities in it. Rock salt is mined from

the underground deposits just like coal. The rock salt which we dig out today from the earth was

formed when the ancient seas dried up by evaporation, thousands of years ago.

Uses of Common Salt (or sodium Chloride)

Common salt (sodium chloride) is used as a raw material for making a large number of useful

chemicals in industry such as: Sodium hydroxide (caustic soda0, sodium carbonate (washing soda),

sodium hydrogen carbonate (baking soda), hydrochloric acid, hydrogen, chlorine, and sodium metal.

Common salt (sodium chloride) is used in cooking food. It improves the flavor of food. Sodium

chloride is required by our body for the working of nervous system, the movement of muscles, and

the production of hydrochloric acid in the stomach for the digestion of food.

Common salt (sodium chloride) is used in the manufacture of soap.

Common salt (sodium chloride) is used to melt ice which collects on the roads during winter in cold

countries.

CHEMICALS FROM COMMON SALT

Sodium hydroxide (caustic soda), sodium carbonate (washing soda), and sodium hydrogen carbonate

(Baking soda).

SODIUM HYDROXIDE

Sodium hydroxide is commonly known as caustic soda. The chemical formula of sodium hydroxide is

NaOH. Sodium hydroxide is a very important basic chemical which is used as a starting material for

making many other chemicals.

Production of Sodium Hydroxide

Sodium hydroxide is produced by the electrolysis of a concentrated aqueous solution of sodium

chloride (which is called brine).

When electricity is passed through a concentrated solution of sodium chloride (called brine), it

decomposes to form sodium hydroxide, chlorine and hydrogen:

2NaCI (aq)

Sodium

chloride

+ 2H2O (I)

Water

Electricity

(Electrolysis)

2NaOH (aq)

Sodium

hydroxide

(Caustic soda)

+ CI2 (g)

Chlorine

+ H2 (g)

Hydrogen

Chlorine gas is produced at the anode (positive electrode) and hydrogen gas is produced at the

cathode (negative electrode). Sodium hydroxide solution is formed near the cathode.

The process of electrolysis of sodium chloride solution is called chlor-alkali process because of the

products formed: chlor for chlorine and alkali for sodium hydroxide. The three very useful products

obtained by the electrolysis of sodium chloride solution called brine (or chlor-alkali process) are

sodium hydroxide, chlorine and hydrogen.



Uses of Sodium Hydroxide

Sodium hydroxide is used for making soaps and detergents.

Sodium hydroxide is used for making artificial textile fibres (such as rayon).

Sodium hydroxide is used in the manufacture of paper.

Sodium hydroxide is used in purifying bauxite ore from which aluminium metal is extracted.

Sodium hydroxide is used in de-greasing metals, oil refining and making eyes dyes and bleaches.

Uses of Chlorine

Chlorine is used to sterilise drinking water supply, and the water in swimming pools. This is because

chlorine is a disinfectant (which kills germs like bacteria present in water and makes it safe).

Chlorine is used in the production of bleaching powder.

Chlorine is used in the production of hydrochloric acid.

Chlorine is used to make plastics such as polyvinyl chloride (PVC), pasticides, chlorofluorocarbons

(CFCs), Chloroform, carbon tetrachloride, paints and dye-stuffs.

Chlorine is used for making solvents for drycleaning (such as trichloroethane).

Uses of Hydrogen

Hydrogen is used in the hydrogenation of oils to obtain solid fats (called vegetable ghee or

margarine).

Hydrogen is used in the production of hydrochloric acid.

Hydrogen is used to make ammonia for fertilisers.

Hydrogen is used to make methanol (CH3OH).

Liquid hydrogen is used as a fuel for rockets.

Hydrogen and chlorine, combine to produce another very important chemical called hydrochloric

acid (HCI).

Uses of Hydrochloric Acid

Hydrochloric acid is used for cleaning iron sheets before tin-plating or galvanization.

Hydrochloric acid is used in the preparation of chlorides such as ammonium chloride (which is used

in dry cells).

Hydrochloric acid is used in medicines and cosmetics.

Hydrochloric acid is used in textile, dyeing and tanning industries.

Hydrochloric acid is used in making plastics like polyvinyl chloride (PVC).

Bleaching agent used in making household bleaches and for bleaching fabrics: Sodium hydroxide and

chlorine, combine together to produces another chemical called sodium hydrochlorite (NaCIO). Sodium

hypochlorite is a bleaching agent which is used in making ‘household bleaches’ and for ‘bleaching

fabrics’.

WASHING SODA



Washing soda is sodium carbonate containing 10 molecules of water of crystallisation. That is,

washing soda is sodium carbonate decahydrate. The formula of washing soda is Na2CO3. 10H2O.

Sodium carbonate which does not contain any water of crystallization is called anhydrous sodium

carbonate, Na2CO3. Anhydrous sodium carbonate (Na2CO3) is commonly known as ‘soda ash’.

Production of Washing Soda

A cold and concentrated solution of sodium chloride (called brine) is reacted with ammonia and

carbon dioxide to obtain sodium hydrogen carbonate:

NaCI

Sodium

Chloride

(Common

Salt)

+ NH3

Ammonia

+ H2O

Water

+ CO2

Carbon

dioxide

NaHCO3

Sodium hydrogen

carbonate

+ NH4CI

Ammonia

chloride

Sodium hydrogen carbonate formed is only slightly soluble in water, so it precipitates out as a solid.

Sodium hydrogen carbonate is separated by filtration, dried and heated. On heating, sodium

hydrogen carbonate decomposes to form sodium carbonate:

2NaHCO3

Sodium

hydrogen

carbonate

Heat

Na2CO3

Sodium

carbonate

(Soda ash)

+ CO2

Carbon dioxide

+ H2O

Water

The anhydrous sodium carbonate obtained here is called soda ash.

Anhydrous sodium carbonate (soda ash) is dissolved in water and recrystallised to get washing soda

crystals containing 10 molecules of water of crystallization:

Na2CO3

Anhydrous sodium

carbonate

(Soda ash)

+ 10H2O

Water

Na2CO3.10H2O

Sodium carbonate decahydrate

(washing soda)

Properties of Washing Soda

Washing soda is a transparent crystalline solid.

Washing soda is one of the few metal carbonates which are soluble in water.

The solution of washing soda in water alkaline which turns red litmus to blue.

Detergent properties (or Cleansing properties). Washing soda has detergent properties (or cleansing

properties) because it can remove dirt and grease from dirty clothes, etc. Washing soda attacks dirt

and grease to form water soluble products, which are then washed away on rinsing with water.

Uses of sodium Carbonate (or washing Soda)

Sodium carbonate (or washing soda) is used as a cleansing agent’’ for domestic purposes like

washing clothes. In fact, sodium carbonate is a component of many dry soap powders.

Sodium carbonate is used for removing permanent hardness of water.

Sodium carbonate is used in the manufacture of glass, soap and paper.

Sodium carbonate is used in the manufacture of sodium compounds such as borax.



BAKING SODA

The chemical name of baking soda is sodium hydrogen carbonate. The formula of baking soda is

NaHCO3. It is called sodium bicarbonate.

Production of Sodium Hydrogen Carbonate

Sodium hydrogen carbonate is produced on a large scale by reacting a cold and concentrated

solution of sodium chloride (called brine) with ammonia and carbon dioxide:

NaCI

Sodium

chloride

(Common

salt)

+ NH3

Ammonia

+ H2O

Water

+ CO2

Carbon

dioxide

NaHCO3

Sodium

hydrogen

carbonate

(Baking soda)

+ NH4CI

Ammonium

chloride

Properties of Sodium Hydrogen Carbonate (or Baking Soda)

Sodium hydrogen carbonate consists of white crystals which are sparingly soluble in water.

Sodium hydrogen carbonate is a mild, non-corrosive base. The solution of sodium hydrogen

carbonate in water is mildly alkaline.

Action of Heat: When solid sodium hydrogen carbonate (or its solution) is heated, then it

decomposes to give sodium carbonate with the evolution of carbon dioxide gas:

2NaHCO3

Sodium hydrogen carbonate

(Baking soda)

Heat

Na2CO3

Sodium carbonate

+ CO2

Carbon dioxide

+ H2O

Water

Uses of sodium Hydrogen carbonate (or Baking Soda)

Sodium hydrogen carbonate is used as an antacid in medicine to remove acidity of the stomach.

Being alkaline, sodium hydrogen carbonate neutralizes the excess acid present in the stomach and

relieves indigestion.

Sodium hydrogen carbonate (or baking soda) is used in making baking powder (used in making

cakes, bread, etc).

Sodium hydrogen carbonate (or baking soda) is used in fire extinguishers.

Baking powder

Baking powder is a mixture of baking soda (sodium hydrogen carbonate) and a mild, edible acid such

as tartaric acid.

How does baking powder makes the dough soft and spongy

When baking powder mixes with water (present in dough made for baking cake or bread), then

sodium hydrogen carbonate reacts with tartaric acid to evolve carbon dioxide gas.

NaHCO3 (aq)

Sodium hydrogen

carbonate (Baking

soda)

+ H+ (aq)

Hydrogen ions

(From tartaric

acid)

Na+ (aq)

Sodium ions

(From sodium

tartarate salt)

+ CO2 (g)

Carbon

dioxide

+ H2O (I)

Water



The carbon dioxide gas produced gets trapped in the wet dough and bubbles out slowly making the

cake (or bread) to ‘rise’ and becomes soft and spongy.

What will happen if baking powder is not added during the making of cakes and bread?

If baking powder is not added in the preparation of cake (or bread), then the cake (or bread)

obtained will be hard and quite small in size.

What will happen if only baking soda is added during the making of cakes and bread? What is the

advantage of using baking powder?

If only sodium hydrogen carbonate (baking soda) is used in making cake (or bread), then sodium

carbonate formed from it by the action of heat (during baking) will give a bitter taste to cake (or

bread).

The advantage of using baking powder is that tartaric acid present in it can react with any sodium

carbonate formed and neutralize it. And the sodium tartarate salt formed by neutralization has a

pleasant taste.

Why baking powder only acts when it is mixed with water?

As long as baking powder is dry, the sodium hydrogen carbonate and tartaric acid present in it do

not react with each other. They react only in the presence of water.

Difference between baking soda and baking powder

Baking soda is a single compound: Sodium hydrogen carbonate. On the other hand, baking powder is

a mixture of sodium hydrogen carbonate and a solid, edible acid such as tartaric acid (or citric acid).

Fire extinguishers

Structure: Soda acid type fire extinguishers contain a solution of sodium hydrogen carbonate and

sulphuric acid in separate containers inside them.

Working: When the knob of the fire extinguisher is pressed (or when the fire extinguisher is

inverted), then sulphuric acid mixes with sodium hydrogen carbonate solution to produce a lot of

carbon dioxide gas. The pressure of this carbon dioxide gas force a stream of liquid to fall on the

burning substance. The carbon dioxide gas (coming out along with the liquid) forms a blanket around

the burning substance and cuts off the supply of air to the burning substance. Since the supply of air

is cut off, the process of burning stops and fire gets extinguished. The stream of liquid falling on the

burning substance also helps in putting off fire by cooling the burning substances to below its

ignition temperature.

BLEACHING POWDER

A substance which removes colour from coloured substances and makes them colourless is called a

bleaching agent.

Bleaching powder is calcium oxychloride. The chemical formula of bleaching powder is CaOCl2. It is

also called chloride of lime.

Preparation of Bleaching Powder



Bleaching powder is prepared by passing chlorine gas over dry slaked lime:

Ca(OH)2

Calcium

hydroxide

(Slaked lime)

+ CI2

Chlorine

CaOCI2

Calcium oxychloride

(Bleaching powder)

+ H2O

Water

Properties of Bleaching Powder

Bleaching powder is a white powder which gives a strong of chlorine.

Bleaching powder is soluble in cold water. The small insoluble portion always left behind is the lime

present in it.

Bleaching powder reacts with dilute acids to produce chlorine. When bleaching powder is treated

with an excess of a dilute acid, all the chlorine present in it is liberated.

What happens when bleaching powder reacts with dilute acid: When bleaching powder is treated

with an excess of dilute sulphuric acid, all the chlorine present in it is liberated:

CaOCI2

Calcium

oxychloride

(Bleaching

powder)

+ H2SO4

Sulphuric acid

(Dilute)

CaSO4

Calcium

sulphate

+ CI2

Chlorine

+ H2O

Water

The chlorine produced by the action of a dilute acid on bleaching powder acts as a bleaching agent.

Thus, the real bleaching agent present in bleaching powder is chlorine.

The bleaching action of chlorine is due to its oxidising property. Some coloured substances turn

colourless when oxidised by chlorine. Actually, bleaching powder is an arrangement for storing

chlorine. This is because chlorine gas itself is difficult to store and utilize.

Uses of Bleaching Powder

Bleaching powder is used for bleaching cotton and linen in textile industry and for bleaching wood

pulp in paper industry. It is also used for bleaching washed clothes in laundry (Laundry is a place

where clothes are washed and pressed). The bleaching action bleaching powder is due to the

chlorine released by it.

Bleaching powder is used for disinfecting drinking water supply. That is, for making drinking water

free from germs.

Bleaching powder is used for the manufacture of chloroform (CHCI3).

Bleaching powder is used for making wool unshrinkable.

Bleaching powder is used as an oxidising agent in many chemical industries.

PLASTER OF PARIS

Plaster of Paris is calcium sulphate hemihydrates (calcium sulphate half-hydrate). The formula of

plaster of Paris is CaSO4. 1

2 H2O. the name plaster of Paris came from the fact that it was first of all

made by heating gypsum which was mainly found in Paris.

Preparation of Plaster of Paris



When gypsum is heated to a temperature of 1000C (373 K), it loses three- fourths of its water of

crystallization and forms plaster of Paris:

CaSO4. 2H2O

Gypsum

Heat to 1000C

(373K) CaSO4.

1

2H2O

Plaster of Paris

+ 11

2H2O

Water

2(CaSO4.2H2O)

Gypsum

Heat to 100oC

(373 K)

2CaSO4.H2O

Plaster of Paris

+ 3H2O

Water

Why the heating of gypsum is controlled?

In the preparation of plaster of Paris heating of gypsum should be controlled carefully. The

temperature during the heating of gypsum should not be allowed to go above 1000C (or above

373K). This is because if gypsum is heated above 1000C (or above 373 K), then all its water of

crystallisation is eliminated and anhydrous calcium sulphate (CaSO4) called dead burnt plaster is

formed. The anhydrous calcium sulphate (or dead burnt plaster) does not set like plaster of Paris on

adding water.

Properties of Plaster of Paris

Plaster of Paris is a white powder.

Plaster of Paris has a very remarkable property of setting into a hard mass on wetting with water. So,

when water is added to plaster of Paris, it sets into a hard mass in about half an hour. The setting of

plaster of Paris is due to its hydration to form crystals of gypsum which set to form a hard, solid

mass:

CaSO4.1

2H2O

Plaster of Paris

+ 11

2H2O

Water

CaSO4.2H2O

Gypsum

(Sets as hard mass)

Why POP is used in making of statues: The setting of plaster of Paris is accompanied by a slight

expansion in volume due to which it is used in making casts for statues, toys etc.

Why POP is stored in moisture proof containers: Plaster of Paris should be stored in a moisture-proof

container. This is because the presence of moisture can cause slow setting of plaster of Paris by bringing

about its hydration. This will make the plaster of Paris unless after some time.

Uses of Plaster of Paris

Plaster of Paris is used in hospitals for setting fractured bones in the right position to ensure correct

heating. It keeps the fractured bone straight. This use is based on the fact that when plaster of Paris

is mixed with a proper quantity of water and applied around the fractured limbs, it sets into a hard

mass. In this way, it keeps the bone joints in a fixed position. It is also used for making casts in

dentistry.

Plaster of Paris is used in making toys, decorative materials, cheap ornaments, cosmetics, black-

board chalk and casts for statues.

Plaster of Paris is used as a fire-proofing material.

Plaster of Paris is used in chemistry laboratories for sealing air-gaps in apparatus where air-tight

arrangement is required.



Plaster of Paris is used for making surfaces (Like the walls of a house) smooth before painting them,

and for making ornamental designs on the ceilings of houses and other buildings.

WATER OF CRYSTALLISATION: HYDRATED SALTS

The water molecules which form part of the structure of a crystal (of a salt) are called water of

crystallization.

The salts which contain water of crystallization are called hydrated salts. Every hydrated salt has a

‘fixed number’ of molecules of water of crystallistaion in its one ‘formula unit’.

Examples:

Copper sulpahte crystals contain 5 molecules of water of crystallisation in one formula unit. Hence

written CuSO45H2O. It is called copper sulphate pentahydrate (‘Pentahydrate’ means’ five molecules

of water’).

Sodium carbonate crystals (washing soda crystals) 10 molecules of water of crystallisation per

formula unit and hence written as Na2CO3.10H2O. This is called sodium carbonate decahydrate

(‘Decahydrate’ means’ ten molecules of water’).

Calcium sulphate crystals (gypsum crystals) contain 2 molecules of water of crystallization in one

formula unit and hence written as CaSO4.2H2O. It is called calcium sulphate dehydrate (‘Dihydrate’

means ‘two molecules of water’).

Iron sulphate crystals contain 7 molecules of water of crystallization per formula unit and hence

written as FeSO4.7H2O. It is called iron sulphate heptahydrate (‘Heptahydrate’ means’ seven

molecules of water’).

Importance of Water of crystallization: Water of crystallization is a part of ‘crystal structure’ of a

salt. Since water of crystallisation is not free water, it does not wet the salt. Thus, the containing

water of crystallisation appear to be perfectly dry.

The water of crystallisation gives the crystals of the salts their ‘shape’ and, in some cases, imparts

them ‘colour’. Example, the presence of water of crystallisation in copper sulphate crystals imparts

them a blue colour. Thus, CuSO4.5H2O is blue in colour. Similarly, the presence of water of

crystallisation in iron sulphate crystals imparts them a green colour. So FeSO4.7H2O is green in

colour. Sodium carbonate crystals (Na2CO3.10H2O) and calcium sulphate crystals (CaSO4.2H2O) are,

however, white.

Action of Heat on Hydrated Salts

When hydrated salts are heated strongly, they lose their water of crystallisation. By losing water of

crystallisation, the hydrated salt lose their regular shape and colour, and become colourless powdery

substances. The salts which have lost their water of crystallization are called anhydrous salts. Thus,

the anhydrous salts have no water of crystallisation. When water is added to an anhydrous salt, it

becomes hydrated once again, and regains its colour.

CuSO4.5H2O

Hydrated copper

sulphate

(Blue)

Heat

CuSO4

Anhydous copper sulphate

(White)

+ 5H2O

Water

(Goes away)

The dehydration of copper sulphate crystals is a reversible process.



CuSO4

Anhydrous copper

sulphate

(White)

+ 5H2O

Water

CuSO4.5H2O

Hydrated copper

sulphate

(Blue)

Anhydrous copper sulphate turns blue on adding water.

How many elements are known at present? How many groups they are divided? On what basis they

are divided?

There are 118 chemical elements known at present. On the basis of their physical and chemical

properties, all the elements can be divided into two main groups: metals and non-metals.

What is the meaning of malleable, ductile and brittle?

Malleable mean which can be beaten with a hammer to form thin sheets (without breaking). Ductile

mean which can be stretched (or drawn) to form thin wires.

Brittle mean which breaks into pieces on hammering or stretching.

METALS

Define metals: Metals are the elements that conduct heat and electricity, and are malleable and ductile.

Metals are also lustrous (shiny), hard, strong, heavy and sonorous (which make ringing sound when

struck). Some of the example of metals are : Iron, Aluminium, Copper, Silver, Gold, Platinum, Zinc, Tin,

Lead, Mercury, Sodium, Potassium, Calcium and Magnesium.

Liquid metal: mercury is a liquid metal.

What type of ions are formed by metals: Metals are the elements (except hydrogen) which form

positive ions by losing electrons (or donating electrons). For example , aluminium (Al) is a metal which

forms positively charged aluminium ions (Al3+) by losing electrons.

Why metals are known as electropositive elements: Metals are known as electropositive elements

because they can form positive ions by losing electrons.

The most abundant metal in the earth's crust is aluminium, which constitutes about 7% of the earth's

crust.

The second most abundant metals in the earth's crust is iron, which constitutes about 4% of the

earth's crust.

The major metals in the earth's crusts in the decreasing order of their abundance are: Aluminium,

Iron, Calcium, Sodium, Potassium and Magnesium.

Metals and Non Metals



NON-METALS

Define: Non-metals are the elements that do not conduct heat and electricity, and neither malleable nor

ductile. They are brittle. Non-metals are not lustrous (not shiny), they have dull appearance. Non-metals

are generally soft, and not strong. They are light substances and non-sonorous (which do not make

ringing sound when struck). Some of the examples of non-metals are : Carbon , Sulphur, Phosphorus,

Silicon, Hydrogen, Oxygen, Nitrogen, Chlorine, Bromine, Iodine, Helium, Neon, and Argon.

Number of non metals: There are 22 non-metals. Out of these, 10 non-metals are solids, 1 non-metal

(bromine) is a liquid whereas the remaining 11 non-metals are gases.

What type of ions are formed by non-metals: Non-metals are the elements which form negative ions

by gaining electrons ( or accepting electrons). For example, oxygen (O) is a non-metal which forms

negatively charged oxide ions (O2-) by gaining electrons.

Why non-metals are known as electronegetive elements: Non-metals are known as electronegative

elements because they can form negative ions by gaining electrons. Hydrogen (H) is the only non-metal

element which loses electrons to form positive ions.

Importance of non-metals:

Though non-metals are small in number as compared to metals, but they play a very important role

in our daily life.

Carbon is one of the most important non-metals because all the life on this earth is based on carbon

compounds. This is because the carbon compounds like proteins, fats, carbohydrates, vitamins and

enzymes, etc, are essential for the growth and development of living organisms.

Another non-metal, oxygen is equally important for the existence of life. This is because the

presence of oxygen gas in the air is essential for breathing to maintain life. It is also necessary for

the combustion (or burning) of fuels which provide us energy for various purposes.

Nitrogen is an inert gaseous non-metal whose presence in air reduces the rate of combustion and

makes it safe.

Another non-metal, sulphur is present in many of the substances found in plants and animals. For

example, sulphur is present in hair, onion, garlic and wool, etc.

Non-metals are required to make vegetable ghee, fertilizers, acids, explosives and fungicides, etc.

The most abundant non-metal in the earth's crust is oxygen, which constitutes about 50% of the

earth's crust.

The second most abundant non-metal in the earth's crust is silicon, which constitutes about 26% of

the earth's crust.

The major non-metal in the earth's crust in the decreasing order of their abundance are: Oxygen,

Silicon Phosphorus and Sulphur.

PHYSICAL PROPERTIES OF METALS

1. Malleability

Define: The property which allows the metals to be hammered into thin sheets is called malleability.

Property: Metals are malleable, that is, metals can be beaten into thin sheets with a hammer (without

breaking).

Best malleable metals: Gold and silver.

Highly malleable metals: Aluminium and Copper.

Examples and uses:

Silver metal can be hammered into thin silver foils because of its high malleability. The silver foils are

used for decorating sweets.

Aluminium metal is quite malleable and can be converted into thin sheets called aluminium foils.

Aluminium foils are used for packing food items like biscuits, chocolates, medicines, cigarettes, etc.

Milk bottle caps are also made of aluminium foil. Aluminium sheets are used for making cooking

utensils.



Copper metal is also highly malleable. So, copper sheets are used to make utensils and other

containers.

Iron is also a quite malleable metal which can be hammered to form iron sheets. These iron sheets

are used to make boxes, buckets, drums and water tanks, etc.

2. Ductility

Property: Metals are ductile, that is, metals can be drawn or stretched into thin wires.

Examples and uses:

Gold is the most ductile metal.

Silver is also among the best ductile metals.

Copper and aluminium metals are also very ductile and can be drawn into thin copper wires and

aluminium wires (which are used as electric wires).

Iron, magnesium and tungsten metals are also quite ductile and can be drawn into thin wires. Iron

wires are used for making wore gauzes. Magnesium wires are used in science experiments in the

laboratory. And thin wires of tungsten metal are used for making the filaments of electric bulbs.

3. Good conductors of heat

Property: Metals are good conductors of heat. Metals allow heat to pass through them easily.

Examples and uses:

Silver metal is the best conductor of heat. It has the highest thermal conductivity.

Copper and aluminium metals are also very good conductors of heat. The cooking utensils and

water boilers, etc., are usually made of copper or aluminium metals because they are very good

conductors of heat.

The poorest conductor of heat among the metals is lead.

Mercury metal is also a poor conductor of heat.

How a metal conducts heat: When a metal is heated, its atoms gain energy and vibrate more vigorously.

These electrons can move through the metal. When the energetic electrons and atoms of the metal (some

distance away from the end that is being heated). In this way, heat is conducted from one end of the

metal to its other end.

4. Good conductors of electricity

Property: Metals are good conductors of electricity. Metals allow electricity (or electric current) to pass

through them easily.

Examples and uses:

Silver metal is the best conductor of electricity.

Copper metal is the next best conductor of electricity followed by gold, aluminium and tungsten.

The electric wires are made of copper and aluminium metals because they are very good

conductors of electricity.

The metals like iron and mercury offer comparatively greater resistance to the flow of current, so

they have lower electrical conductivity.

How a metal conducts electricity: Metals are good conductors of electricity because they contain

free electrons. These free electrons can move easily through the metal and conduct electric current.

By which material are wires covered with and why: The electric wires that carry current in our

homes have a covering of plastic such as Poly Vinyl chloride (PVC). Polyvinyl chloride is an

insulator. It does not allow electric current to pass through it. The electric wires have a covering of

an insulating material (like PVC) around them so that even if we happen to touch them, the current

will not pass through our body and hence we will not get an electric shock.

5. Lustrous



Define: The property of a metal of having a shining surface is called 'metallic lustre' (chamak).

Use of the metallic luster: The shiny appearance of the metals makes them useful in making jewellery

and decoration pieces.

Property: Metals are lustrous (or shiny), and can be polished. They have a shining surface.

Examples and uses:

Gold, silver and copper are shiny metals and they can be polished. Gold and silver are used for

making jewellery because they are bright and shiny. The shiny appearance of metals makes them

good reflectors of light.

Silver metal is an excellent reflector of light. This is why it is used in making mirrors.

Why metals lose there shine: The metals lose their shine or brightness on keeping in air for a long time

and acquire a dull appearance due to the formation of a thin layer of oxide , carbonate or sulphide on

their surface (by the slow action of the various gases present in air). We say that the metal surface has

been corroded.

How can we get the shine of the metals back: If we rub the dull surface of a metal object with a sand

paper, then the outer corroded layer is removed and the metal object becomes shiny and bright once

again.

6. Hardness

Property: Metals are generally hard (except sodium and potassium which are soft metals)

Examples: Most of the metals are hard. But all the metals are not equally hard. The hardness varies from

metal to metal. Most of the metals like iron, copper, aluminium ,etc, are very hard. They cannot be cut

with a knife.

Exception: Sodium and potassium are soft metals which can be easily cut with a knife.

7. Strength

Property: Metals are strong (except sodium and potassium metals which are not strong).

Examples and uses: Iron metal (in the form of steel) is very strong. Due to this iron metal is used in the

construction of bridges, buildings, railway lines, girders, machines, vehicles and chains, etc.

Exception: sodium and potassium metals are not strong.

8. State of metals:

Property: Metals are solids at room temperature (except mercury which is a liquid metals).

9. Melting points and boiling points

Property: Metals have high melting points and boiling points (except sodium and potassium metals

which have low melting and boiling points).

Examples: Iron metal has a high melting point of 1535°C. This means that solid iron melts and turns into

liquid iron ( or molten iron) non heating to a high temperature of 1535° C. Copper metal has also a high

melting point of 1083° C.

Exceptions: Sodium and potassium metals have low melting points (of 98°C and 64°C respectively).

Gallium and cesium metals also have low melting points (of 30°C and 28°C respectively). The melting

points of gallium and cesium metals are so low that they start melting in hand (by the heat of our body)

10. Densities

Property: Metals have high densities, we mean that metals are heavy substances (except sodium and

potassium metals which have low densities.

Examples: the density of iron is 7.8 g /cm3 which is quite high so, iron metal is a heavy substance.



Exception: Sodium and potassium metals have low densities (of 0.97 g/cm3 and 0.86 g/cm3 respectively.

They are very light metals.

11. Sonorous

Property: Metals are sonorous. That is, metals make sound when hit with an object.

Define: Sonorous means capable of producing a deep or ringing sound. The property of metals of being

sonorous is called sonorousness or sonorousity.

Use of sonorousness: It is due to the property of sonorousness (or sonority) that metals are used for

making bells, and strings (wires) of musical instruments like sitar and violin.

12. Colour

Metals usually have a silver or grey colour (except copper and gold).

Copper has a reddish-brown colour whereas gold has a yellow colour.

PHYSICAL PROPERTIES OF NON-METALS

1. Malleability and Ductility

Non-metals are neither malleable nor ductile. Non-metals are brittle (break easily)

Solid non-metals can neither be hammered into thin sheets nor drawn into thin wires. Non-metals are

brittle which means that non-metals break into pieces when hammered or stretched. For example,

sulphur and phosphorus are beaten with a hammer or stretched, they break into pieces (they do not

form thin sheets or wires). Carbon is also a solid non-metal which is brittle. The property of being brittle

(breaking easily) is called brittleness. Thus, brittleness is a characteristic property of non-metals.

2. Bad conductors of heat and bad conductors of electricity

Non-metals do not conduct heat and electricity.

Non-metals do not conduct heat and electricity because unlike metals, they have no free electrons (which

are necessary to conduct heat and electricity). For example, sulphur and phosphorus are non-metals

which do not conduct heat and electricity.

Exception: Carbon (in the form of graphite) is the only non-metal which is a good conductor of

electricity. Since graphite (which is an allotropic form of carbon) is a good conductor is electricity, it is

used for making electrodes.

3. Shine

Non-metals are not lustrous (not shiny). They are dull

Non-metals do not have a shining surface. The solid non-metals have a dull appearance. For example,

sulphur and phosphorus are non-metals which have no luster, that is they do not have a shining surface.

They appear to be dull.

Exception: Iodine is a non-metal having lustrous appearance. It has a shining surface. (like that of

metals).

4. Hardness

Non-metals are generally soft (except diamond which is an extremely hard non-metal)

Most of the solid non-metals are quite soft. For example, sulphur and phosphorus are solid non-metals

which are quite soft.

Exception: Only one non-metals carbon (in the form of diamond) is very hard.

5. Strength



Non-metals are not strong. They are easily broken.

Graphite is a non-metal which is not strong. It has low strength. So, when a large weight is placed on a

graphite sheet it gets snapped (breaks).

6. State

Non-metals may be solid, liquid or gases at the room temperature.

Non-metals can exist in all the three physical states : solid, liquid and gaseous. For example, carbon,

sulphur and phosphorus are solid non-metals, bromine is a liquid non-metals; whereas hydrogen,

oxygen, nitrogen and chlorine are gaseous non-metals.

7. Melting points and boiling points

Non-metals have comparatively low melting pointing points and boiling points (except diamond which is

a non-metal having a high melting point and boiling point).

The melting point of sulphur is 115°C which is quite low.

Exception: The melting point of diamond is, however, more than 3500°C, which is very high.

8. Density

Non-metals have low densities, that is, non-metals are light substances.

The density of sulphur is 2 g/cm3 .

9. Non-metals are non-sonorous. They do not produce sound when hit with an object

10. Colour

Non-metals have many different colours

Sulphur is yellow, phosphorus is white or red, graphite is black, chlorine is yellowish-green whereas

hydrogen and oxygen are colourless.

CHEMICAL PROPERTIES OF METALS

1. Reaction of Metals with Oxygen (of Air)

Metal + Oxygen → Metal oxide

(From air) (Basic oxide)

Metals react with oxygen to form metal oxides. Metal oxides are basic in nature. Some of the metal oxides

react with water to form alkalis. Metal oxides, being basic, turn red litmus solution blue.

Factor affecting vigour of reaction: The vigour of reaction with oxygen depends on the chemical

reactivity of metal. Some metals react with oxygen even at room temperature, some react on heating,

whereas still others react only on strong heating.

How sodium and potassium react with oxygen: Sodium metal reacts with the oxygen of air at room

temperature to form a basic oxide called sodium oxide.

4Na (s) + O2(g) → 2Na2O(s)

Sodium Oxygen Sodium oxide

(Metal) (From air) (Basic oxide)

Potassium metal (K) also reacts with the oxygen (O2) of air at room temperature to form a basic oxide,

called potassium oxide (K2O).



Why potassium and sodium, potassium and lithium catch fire when kept in air: Potassium and

sodium metals are so reactive that they react vigorously with the oxygen (of air). They catch fire and

start buring when kept open in the air. In fact, potassium metal and sodium metal are stored in kerosene

oil to prevent the reaction with oxygen.

Just like sodium and potsssium metals, lithium metal is also stored under kerosene oil to prevent its

reaction with oxygen, moisture and carbon dioxide of air (so as to protect it).

Solubility of metal oxides in water: Most of the metal oxides are insoluble in water. But some of the

metal oxides dissolve in water to form alkalis. Sodium oxide and potassium oxide are the two metal

oxides which are soluble in water. They dissolve in water to form alkalis.

How can we show that sodium oxide, potassium oxide and lithium oxide are basic in nature?

Na2O(s) + H2O (l) 2NaOH(aq)

Sodium oxide Water Sodium hydroxide

(Basic oxide) (An alkali)

K2O(s) + H2O (l) 2KOH(aq)

Potassium oxide Water Potassium hydroxide

(Basic oxide) (An alkali)

Reaction of magnesium with oxygen: Magnesium metal does not react with oxygen at room

temperature. But on heating, magnesium metal burns in air giving intense heat and light to form a basic

oxide called magnesium oxide (Which is a white power). 2Mg (s) + O2(g) → MgO(s)

Magnesium Oxygen Magnesium oxide

(Metal) (From air) (Basic oxide)

How can we say that magnesium is less reactive than sodium: Heat is required for the reaction of

magnesium with oxygen, it means magnesium is less reactive than sodium (or potassium).

How can we say that Magnesium oxide is basic in nature: Magnesium oxide dissolves in water

partially to form magnesium hydroxide solution :

MgO(s) + H2O (l) Mg(OH)2(aq)

Magnesium oxide Water Magnesium hydroxide

(A base)

Reaction of aluminium with oxygen: Aluminium metal burns in air, on heating, to form aluminium

oxide :

Al (s) + O2 (g) Al2O3

Aluminium Oxygen Aluminium oxide

(Metal) (Form air) (Amphoteric oxide)

Define: Those metal oxide which show basic as well as acidic behavior are known as amphoteric

oxides. Example: Aluminium metal and Zinc oxide are amphoteric in nature (which shows basic as well

as bases to form salts and water).

How can we show that aluminium oxide is amphoteric in nature

Aluminium oxide reacts with hydrochloric acid to form aluminium chloride (salt) and water:

Aluminium oxide Hydrochloric acid Aluminium chloride Water

In this reaction, aluminium oxide behaves as basic oxide (because it reacts with an acid to form salt and

water).



Aluminium oxide reacts with sodium hydroxide to form sodium aluminate (salt) and water:

Aluminium oxide sodium hydroxide sodium aluminate Water

In this reaction, aluminium oxide behaves as an acidic oxide (because it reacts with a base to form salt and

water).

Reaction of zinc with oxygen: Zinc metal burns in air only on strong heating to form zinc oxide :

How can we show that zinc oxide is amphoteric in nature

Zinc oxide is an amphoteric oxide which reacts with acids as well as with bases to form salt and water . this is

described below.

(a) Zinc oxide react with hydrochloric acid to form zinc chloride (salt) and water :

In this reaction, Zinc oxide behaves as a basic oxide (because it reacts with an acid to form salt and water).

(b) Zinc oxide reacts with sodium hydroxide to form sodium zincate (salt) and water :

In this reaction, zinc oxide behaves as an acidic oxide (because it reacts with a base to form salt and water).

At ordinary temperature, the surfaces of the metals like magnesium, aluminium, zinc and lead, etc, are

covered with a thin layer of their respective oxides. This oxides layer acts as a protective layer and

prevents further oxidation (or corrosion) of the metal underneath.

Reaction of iron with oxygen: Iron metal does not bun in air even on strong heating. Iron reacts with

the oxygen of air on heating to form iron (II,III) oxide :

A piece of iron metal does not bun in air but iron filings (small particles of iron ) burn vigorously when

sprinkled in the flame of a burner.

Reaction of copper with oxygen: Copper metal also does not burn in air even on strong heating. Copper

reacts with the oxygen of air on prolonged heating to form a black substance copper (II) oxides :

2Zn (s)

Zinc

+ O2 (g)

Oxygen

2ZnO (s)

Zinc oxide

(Amphoteric oxide)

ZnO (s)

Zinc oxide

+ 2HCl (aq)

Hydrochloric acid

(Acid)

ZnCl2 (aq)

Zinc chloride

(Salt)

+ H2O (I)

Water

ZnO (s)

Zinc oxide

+ 2NaOH (aq)

Sodium hydroxide

(Base)

Na2ZnO2 (aq)

Sodium zincate

(Salt)

+ H2O (I)

Water

3Fe (s)

Iron

+ 2O2 (g)

Oxygen

Fe3O4 (s)

Iron (II,III) oxide



2Cu (s)

Copper

+ O2 (g)

Oxygen

2CuO (s)

Copper (II) oxide

2. Reaction of Metal with Water

Metals reacts with water to form a metal hydroxide (or metal oxide) and hydrogen gas.

(a) When a metal reacts with water (cold water of hot water), then the products formed are metal

hydroxide and

hydrogen gas

:

(b) When a metal reacts with steam, then the products formed are metal oxide and hydrogen gas :

Reaction of potassium with water: Potassium reacts violently with cold water to form potassium

hydroxi

de and

hydrog

en gas :

Reaction of sodium with water: Sodium reacts vigorously with cold water forming sodium hydroxide

and

hydroge

n gas :

Sodium metal reacts with water to form sodium hydroxide and hydrogen gas. A lot of heat is also

produced in this reaction. This heat burns the hydrogen gas as well as the sodium metal. The burning of

hydrogen gas causes little explosions.

Reaction of calcium with water: Calcium reacts with cold water to form calcium hydroxide and

hydrogen gas :

Reaction of magnesium with water: Magnesium metal does not react with cold water. Magnesium

reacts with hot water to form magnesium hydroxide and hydrogen :

Reaction of aluminium with water: Aluminium reacts with steam to form aluminium oxide and

hydrogen gas :

Aluminium metal does not react with water under ordinary conditions because of the presence of a thin (but

tough) layer of aluminium oxide on its surface.

Reaction of zinc with water: Zinc reacts with steam to form zinc oxide and hydrogen :

Metal + Water Metal hydroxide + Hydrogen

Metal + Steam Metal Oxide + Hydrogen

2K (s) + 2H2O (I) 2KOH

(aq)

+ H2 (g) + Heat

2Na (s) + 2H2 O (I) 2NaOH (aq) + H2 (g) + Heat

Ca (s)

Calcium

+ 2H2O (I)

Water (cold)

Ca(OH)2 (aq)

Calcium hydroxide

+ H2 (g)

Hydrogen

Mg (s)

Magnesium

+ 2H2O (I)

Water (Hot)

Mg(OH)2 (aq)

Meg. Hydroxide

+ H2 (g)

Hydrogen

2Al (s)

Aluminium

+ 3H2O (g)

Steam

Al2O3 (s)

Aluminium oxide

+ 3H2 (g)

Hydrogen

Zn (s) + H2O (g) ZnO (s) + H2 (g)



Reaction of iron with water: Red -hot iron reacts with steam to form iron (II,III) oxide and hydrogen :

3Fe (s)

Iron

+ 4H2O (g)

Steam

Fe3O4 (s)

Iron (II,III)oxide

+ 4H2 (g)

Hydrogen

Metals like lead, copper , silver, and gold do not react with water (or even steam).

How metals displace hydrogen form water. Water (H2O) is slightly ionized to give hydrogen ions (H+)

and hydroxide ions (OH). Now , when a reactive metal combines with water, it give electrons to reduce

the hydrogen ions of water to hydrogen atoms, which then form hydrogen gas. The unreactive metals

like copper do not give electrons easily, so they are not displace hydrogen form water.

3. Reaction of Metals with Dilute Acids

Metals usually displace hydrogen form dilute acids.

Sodium metal reacts violently with dilute hydrochloric acid to form sodium chloride and hydrogen :

Magnesium reacts quite rapidly with dilute hydrochloric acid forming magnesium chloride and hydrogen

gas :

Mg (s)

Magnesium

+ 2HCl (aq)

Hydrochloric acid

MgCl2 (aq)

Magnesium chloride

+ H2 (g)

Hydrogen

Aluminium metal at first reacts slowly with dilute hydrochloric acid due to the presence of a tough

protective layer of aluminium oxide on its surface. But when the thin, outer oxide layer gets dissolved in

acid , then fresh aluminium metal is exposed which reacts rapidly with dilute hydrochloric acid.

Zinc reacts with dilute hydrochloric acid to give zinc chloride and hydrogen gas

Zn (s)

Zinc

+ 2HCl (aq)

Hydrochloric

acid

ZnCl2 (aq)

Zinc chloride

+ H2 (g)

Hydrogen

Iron reacts slowly with cold dilute hydrochloric acid to give iron (II) chloride and hydrogen gas :

Fe (s)

Iron

+ 2HCl (aq)

hydrochloric acid

FeCl2 (aq)

Iron (II) chloride

+ H2 (g)

Hydrogen

Copper does not react with dilute hydrochloric acid (or dilute sulphuric acid) at all . This shows that

copper is even less reactive less reactive than iron :

Zinc Stream Zinc oxide Hydrogen

Metal + Dilute acid Metal salt + Hydrogen

2Na (s)

Sodium

+ 2Hcl (aq)

Hydrochloric acid

2NaCl (aq)

sodium chloride

+ H2 (g)

Hydrogen

2Al (s)

Aluminium

+ 6HCl (aq)

Hydrochloric acid

2AlCl3 (aq)

Aluminium chloride

+ 3H2 (g)

Hydrogen



Cu (s)

Copper

+ HCl (aq)

Hydrochloric acid (Dilute)

NO reaction

Silver and gold metals also do not react with dilute acids.

How metals displace hydrogen form dilute acids. All those metals which are more reactive than

hydrogen, that is, those metals which lose electrons more easily than hydrogen, displace hydrogen form

dilute acids to produce hydrogen gas. This is due to the fact that the more reactive metals give electrons

easily and these electrons reduce the hydrogen ions of acids to hydrogen gas. The metals like copper and

silver which are less reactive than hydrogen, do not displace hydrogen form dilute acids. Because they do

not give out electrons required for the reduction of hydrogen ions present in acids.

Metals react with dilute sulphuric acid to give metal sulphates and hydrogen gas.

2Na (s)

Sodium

+ H2 SO4 (aq)

Sulphuric acid

→ Na2 SO4 (aq)

Sodium sulphate

+ H2 (g)

Hydrogen

Mg (s)

Magnesium

+ H2 SO4 (aq)

→ MgSO4 (aq)

Magnesium sulphate

+ H2 (g)

2Al (s)

Aluminium

+ 3H2 SO4 (aq) → Al2 (SO4 )3 (aq)

Aluminium sulphate

+ 3H2 (g)

Zn (s)

Zinc

+ H2 SO4 (aq) → Zn SO4 (aq)

Zinc sulphate

+ H2 (g)

Fe (s)

Iron

+ H2 SO4 (aq) → Fe(SO4 )(aq)

Ferrous sulphate

+ H2 (g)

Cu (s) + H2 SO4 (aq) → NO reaction

When a metal react with dilute nitric acid, then hydrogen gas is not evolved, why. Nitric acid is a

strong oxidizing agent. So, as soon as hydrogen gas is formed in the reaction between a metal and dilute

nitric acid, the nitric acid oxidized this hydrogen to water. So, in the reactions of metals with dilute nitric

acid, no hydrogen gas is evolved. Now, when nitric acid acid-oxidizes hydrogen to water, then nitric acid

itself is reduced to any of the nitrogen oxides (such as di-nitrogen monoxide, N2O; nitrogen monoxide,

NO; or nitrogen dioxide, NO2). The type of oxide formed depends on the nature of metal, the temperature

of reaction and concentration of nitric acid.

Very dilute nitric acid, however, reacts with magnesium and manganese metals to evolve hydrogen gas.

This is because the very dilute nitric acid is a weak oxidizing agent which is not able to oxidize hydrogen

to water.

(a) Magnesium reacts with very dilute nitric acid to form magnesium nitrate and hydrogen gas :

Mg (s) + 2HNO3 (aq) → Mg(NO3)2 (aq) + H2 (g)



Magnesium Nitric acid Magnesium Nitrate Hydrogen

(b) Manganese reacts with very dilute nitric acid to form manganese nitrate and hydrogen gas :

Mn (s)

Manganese

+ 2HNO3 (aq)

Nitric acid

→ Mn(NO3)2 (aq)

Manganese Nitrate

+ H2 (g)

Hydrogen

Aqua-Regia

Aqua-regia is a freshly prepared mixture of 1 part of concentrated nitric acid and 3 part of concentrated

hydrochloric acid. Aqua-regia is a highly corrosive, fuming liquid (Corrosive means which can cause

corrosion. Aqua-regia can dissolve all metals. For example, aqua-regia can dissolve even gold and

platinum metals (though concentrated nitric acid or concentrated hydrochloric acid alone cannot

dissolve gold or platinum metals.

The Reactivity Series of Metals (or Activity Series of Metals)

The arrangement of metals in a vertical column in the order of decreasing reactivates is called reactivity

series of metals ( or activity series of metals).

Why Some Metals are More Reaction and Others Less Reactive.

When metals react, they lose electrons to form positive ions. Now, if a metal atom can lose electrons

easily to form positive ions, it will react rapidly with other substances and hence it will be a reactive

metal. On the other hand, if a metal atom loses electrons less readily to form positive ions, it will react

slowly with other substances. Such a metal will be less reactive. For example, sodium atoms lose

electrons readily to form sodium ions, due to which sodium metal is very reactive. On the other hand,

iron atoms losses electrons less readily to form positive ions, so iron metal is less reactive.

Metals Which are More Reactive Than Hydrogen

Those metals which lose electrons more readily than hydrogen are said to be more reactive than

hydrogen. All the metals which have been placed above hydrogen in the reactivity series, lose electrons

more r4eadily than hydrogen, and hence they are more reactive than hydrogen . Thus, the metals which

are more reactive than hydrogen are : Potassium , sodium, Calcium, Magnesium, aluminium, Zinc, Iron,

Tin ,and Lead. These more reactive metals can displace hydrogen from its compounds like water and

acids to form hydrogen gas.

Metals Which are Less Reactive Than Hydrogen.

Those metals which lose electrons less reactily than hydrogen are said to be less reactive than hydrogen

all the metals placed below hydrogen in the reactivity series lose electrons less readily than hydrogen,

are hence they are less reactive than hydrogen. Thus, the metals which are less r4eactive than hydrogen

are Copper, Mercury, silver and Gold. These less reactive metals cannot displace hydrogen from its

compound like water and acids to form hydrogen gas.

4. Reaction of Metals with salt solutions.

A more reactive metal displaces a less reactive metal from its salt solution.

Salt solution of metal B + Metal A → Salt solution of metal A + Metal B.

CuSO4 (aq)

Copper sulphate

+ Zn (s)

Zinc

→ ZnSO4 (aq)

Zinc sulphate

+ Cu (s)

Copper



(Blue Solution) (Silver white)

Reddish

brown

If, however a strip of copper metal is placed in zinc sulphate solution, then no reaction occurs. This is

because copper metal is less reactive than zinc metal and hence cannot displace zinc from zinc sulphate

solution.

If we put silver metal in copper sulphate solution, even then no reaction takes place. This is because

silver metal is less reactive than copper metal and hence cannot displace copper form copper sulphate

solution.

Reaction of Iron with Copper sulphate solution.

When a strip of iron metal (or iron nail) is placed in copper sulphate solution, then the blue colour of

copper sulphate solution fades gradually and red-brown copper metal is formed :

CuSO4 (aq)

Copper (II) sulphate

Blue Solution

+ Fe(s)

Iron

(Grey)

→ FeSO4 (aq)

Iron(II) sulphate

+ Cu (s)

Copper

2AgNO3 (aq)

silver nitrate

Colourless solution

+ Cu (s)

Copper

Red-brown

→ Cu(NO3)2 (aq)

Copper nitrate

Blue solution

+ 2Ag (s)

silver

Greyish-white

CuSO4 (aq)

Copper (II) sulphate

Blue Solution

+ Fe(s)

Iron metal

From iron pot

→ FeSO4 (aq)

Iron(II) sulphate

Greenish solution

+ Cu (s)

Copper

metal

FeSO4 (aq)

Iron (II) sulphate

Greenish Solution

+ Zn (s)

Zinc

Silver white

→ ZnSO4 (aq)

Zinc sulphate

Colourless solution

+ Fe (s)

Iron

(Grey)

5. Reaction of Metal with Chlorine.

Sodium is a metal which reacts vigorously with chlorine to form an ionic chloride called sodium chloride

:

2Na (s)

Sodium

+ Cl2 (g)

Chlorine

→ 2NaCl (s)

Sodium chlorine

Calcium is a metal which reacts vigorously with chlorine to form an ionic chloride called calcium chloride

:

Ca (s)

Calcium

+ Cl2 (g)

Chlorine

→ CaCl2 (s)

Calcium chloride

Magnesium on heating with chlorine readily forms magnesium chloride, which is an ionic chloride:

Mg (s)

Magnesium

+ Cl2 (g)

Chlorine

→ MgCl2 (s)

Magnesium chlodride

Aluminium reacts with chlorine , on heating, to form aluminium chloride :

2Al (s)

Aluminium

+ 3Cl2 (g)

Chlorine

→ 2AlCl3 (s)

Aluminium chlodride

Zinc combines directly chlorine, to form zinc chloride :

Zn (s)

Zinc

+ 3Cl2 (g)

Chlorine

→ ZnCl2 (s)

Zinc chlodride



Iron combines with chlorine, when heated , to form iron (III) chloride :

2Fe (s)

Iron

+ 3Cl2 (g)

Chlorine

→ 2FeCl3 (s)

Iron (III) chlodride

On heating , copper reacts with chlorine to form copper (II) chloride

Cu (s)

Copper

+ 3Cl2 (g)

Chlorine

→ CuCl2 (s)

Copper (II) chlodride

CHEMICAL PROPERTIES OF NON-METALS

Reaction of Non-metal with Oxygen :

Non-metal react with oxygen to form acidic oxides or neutral oxides. Carbon forms an acidic oxide

CO2, Sulphur forms an acidic oxide SO2, and hydrogen forms a neutral, H2O. The non-metal oxides are

covalent in nature which are formed by the sharing of electrons. The acidic oxides of non-metal dissolve

in water to form acids.

C (s)

Carbon (Non-metal)

+ O2 (g)

Oxygen (from air)

CO2 (g)

Carbon dioxide

(Acidic oxide)

The acidic oxide, carbon dioxide, dissolves in water to form an acid called carbonic acid ;

Sulphur is non-metal . When sulphur is burned in air, it react with the oxygen of air to form an acidic

oxide called sulphur dioxide :

S (s)

Sulphur (Acidic oxide)

+ O2 (g)

Oxygen (From air)

SO2 (g)

Sulphur dioxide

The non-metal oxides like CO2 and SO2 turn blue litmus solution red, showing that they are acidic in

nature. These acidic oxides are called acid anhydrides. Phosphorus is also a non-metal which reacts with

the oxygen of air to form an acidic oxide, phosphorus pentoxide (P2O5). Some of the non-metal oxides

which are neutral, being neither acidic nor basic. The neutral non-metal oxides are carbon monoxide, CO,

water, H2O; nitrogen monoxide, NO; and dinitrogen monoxide, N2O.

Phosphorus burns in air with a yellow flame to form phosphorus pentoxide.

Why white phosphorus is stored in water: White phosphorus is stored under water because it burns

spontaneously in air burns spontaneously in air but does not react with water.

Reaction of Non-Metals with water

Non-metals do not react with water (or steam) to involve hydrogen gas. This is because non-metals

cannot give electrons to reduce the hydrogen ions of water into hydrogen gas.

CO2 (g)

Carbon dioxide

+ H2O (I)

water

H2CO3 (aq)

Carbonic acid

2C (s)

Carbon

(Non-metal)

+ O2 (g)

Oxygen

(Insufficient air)

2CO (g)

Carbon monoxide

(Neutral oxide)

2H2 (g)

Hydrogen

(Non-metal)

+ O2 (g)

Oxygen

(From air)

2H2O (1)

Water

(Neutral oxide)



Reaction of Non-Metals with Dilute Acids

Non-metals do not react with dilute acids. In other words, non-metals do not displace hydrogen from

acids. For example, the non-metals like carbon, sulphur and phosphorus do not react with dilute

hydrochloric acid (HCl) or dilute sulphuric acid( H2SO4) to produce hydrogen gas.

Why non-metals are not able to displace hydrogen from acids. In order to displace hydrogen ions

(H+) of an acid and convert them into hydrogen gas, electrons should be supp0lied to the hydrogen ions

(H+) of the acid. Now, a non-metal, being itself an acceptor of electrons, cannot give electrons to the

hydrogen ions of the acid to reduce them to hydrogen gas. And hence the non-metals are not able to

displace hydrogen ions from acids to form hydrogen gas.

Reaction of Non-Metals with Salt Solutions

A more reactive non-metal displaces a less reactive non-metal from its salt solution.

2NaBr (aq)

Sodium bromide

+ Cl2 (g)

Chlorine 2NaCl (aq)

Sodium chloride

+ Br2(aq)

Bromine

Reaction of Non - Metals with Chlorine.

Non-metals react with chlorine to form covalent chlorides which are non-electrolytes (do not conduct

electricity)

H2(g)

Hydrogen

(Non-metal)

+ Cl2 (g)

Chlorine 2HCl (g)

Hydrogen chloride

(Covalent chloride)

P4 (s)

Phosphorus

(Non-metal)

+ 6Cl2 (g)

Chlorine 4PCl3 (1)

Phosphorus trichloride

(Covalent chloride)

Some phosphorus pendtachloride, PCl5, is also formed in this reaction. carbon (c) is non-metal which reacts

with chlorine to form a covalent chloride called carbon tetrachloride, CCl4, which contains covalent bonds

and does not conduct electricity. Non-metals form covalent chlorides because they cannot give

electrons to chlorine atoms to form chloride ions.

Reaction of Non-Metals with Hydrogen.

Non-metals react with hydrogen to form covalent hydrides. The non-metal hydrides are formed by the

sharing of electrons, that is, non-metal hydrodes are formed by covalent bonding.

H2 (g)

Hydrogen

+ S (l)

Sulphur

(Non-metal)

H2S (g)

Hydrogen sulphide

(Covalent hydride)

Oxygen is also a non-metal which combines with hydrogen to form a hydride called water, H2O, the

hydride of carbon is methane (CH4), and the hydride of chlorine is hydrogen chloride (HCl). The non-

metal hydrides are covalent compounds formed by the sharing of electrons. Non-metals form covalent

hydrodes because non-metal atoms cannot give electrons to hydrogen atoms to form hydride

ions. No-metal hydrides are liquids or gases.

N2 (g)

Nitrogen

(Non-metal)

+

3H2 (g)

Hydrogen

Fe

2NH3 (g)

Ammonia

(Covalent hydride)



Metals Non-Metals

Differences in Physical Properties

1. Metals are malleable and ductile. That is, metals

can be hammered into thin sheets and drawn into

thin wires.

2. Metals are good conductors of heat and electricity.

3. Metals are lustrous (shiny) and can be polished.

4. Metals are solids at room temperature (except

mercury which is a liquid metal).

5. Metals are strong and tough

1. Non-metals are brittle (break easily). They are

neither malleable nor ductile.

2. Non-metals are bad conductors of heat and

electricity (except graphite which is a good

conductor of electricity).

3. Non-metals are non-lustrous (dull) and cannot be

polished (except iodine which is a lustrous non-

metals).

4. Non-metals may be solid, liquid or gases at the

room temperature.

5. Non-metals are not strong or tough

Differences in Chemical Properties

1. Metals form basic oxides.

2. Metals displace hydrogen from water (or steam).

3. Metals displace hydrogen from dilute acids.

4. Metals form ionic chlorides with chlorine. These

ionic chlorides are electrolytes but non-volatile.

5. Metals usually do not combine with hydrogen.

Only a few reactive metals combine with hydrogen to

form ionic metal hydrides

1. Non-metals form acidic oxides or neutral oxides.

2. Non-metals do not react with water (or steam) and

hence do not displace hydrogen from water (or

steam).

3. Non-metals do not react with dilute acids and

hence do not displace hydrogen from dilute acids.

4. Non-metals form covalent chlorides with chlorine

(which are non-electrolytes but volatile).

5. Non-metals react with hydrogen to form stable,

covalent hydrides.

Use of Metals

Metals are used for a large number of purposes. Some of the uses of metals are given below :

1. Copper and aluminium metals are used to make wires to carry electric current. This is because copper

and aluminium have very low electrical resistance and hence very good conductors electricity.

2. Iron, copper and aluminium metals are used to make house-hold utensils and factory equipment.

3. Iron is used as a catalyst in the preparation of ammonia gas by Haber’s process.

4. Zinc is used for galvanizing iron to protect it from rusting.

5. Chromium and nickel metals are used for electroplating and in the manufacture of stainless steel.

5. The aluminium foils are used in packaging of medicines, cigarettes and food materials.

7. Silver and gold metals are used to make jewellery. The thin foils made of silver and gold are used to

decorate sweets.

8. The liquid metal ‘mercury’ is used in making thermometers.

9. Sodium, titanium and zirconium metals are used in atomic energy (nuclear energy) and space science

projects.

10. Zirconium metal is used in making bullet-proof ally steels.

11. The metals is used in making car batteries.

Uses of Non-Metals

The important uses of non-metals are as follows :

1. Hydrogen is used in the hydrogenation of vegetable oils to make vegetable ghee (or vanaspati ghee).



2. Hydrogen is used in the manufacture of ammonia (whose compounds are used as fertilisers).

3. Liquid hydrogen is used as a rocket fuel.

4. Carbon (in the form of graphite) is used for making the electrodes of electrolytic cells and dry cells.

5. Nitrogen is used in the manufacture of ammonia, nitric acid and fertilisers.

6. Due to its inertness, nitrogen is used to preserve food materials.

7. Compounds of nitrogen like Tri Nitro Toluene (TNT) and nitroglytcerine are used as explosives.

8. Sulphur is used as a fungicide and in making gun powder.

9. Sulphur is used in the vulcanisation of rubber.

HOW DO METALS AND NON-METALS REACT

When metals react with non-metals, they form ionic compounds (which contain ionic bonds). On

the other hand, when non-metals react with other non-metals, they form covalent compounds

(which contain covalent bonds.

The force which links the atoms (or ions) in a molecule is called a chemical bond (or just ‘bond’).

Inertness of Noble Gases

These elements are : Helium, Neon, Argon, Krypton, Xenon and Radon. They are known as noble gases or

inert gases because they are unreactive and do not react with other elements to form compounds. In

other words, inert gases do not form chemical bonds.

Since the noble gases are chemically unreactive, we must conclude that the electron

arrangements in their atoms are very stable which do not allow the outermost electrons to the

part in chemical reactions.

Cause of Chemical Bonding (or Chemical Combination)

The atoms combine with one another to achieve the inert gas electron arrangement and become more

stable. Atoms form chemical bonds to achieve stability by acquiring the inert gas electron configuration.

An atom can achieve the inert gas electron arrangement (or noble gas electron arrangement) in three

ways:

(i) by losing one or more electrons (to another atom)

(ii) by gaining one or more electrons (from another atom)

(iii) by sharing one or more electrons (with another atom)

IONS

An ion is an electrically charged atom (or group of atoms). An ion is formed by the loss or gain of

electrons by an atom, so it contains an unequal number of electrons and protons.

There are two types of ions : cations and anions.

Cations

A positively charged ion is known as cation. sodium ion, Na+, and magnesium ion, Mg2+, are cation

because they are positively charged ions. A cation is formed by the loss of one or more electrons by an

atom.

Na

Sodium atom

– e–

Electron Na+

Sodium ion

(A cation)

Since a cation is formed by the removal of electrons from an atom, therefore a cation contains less

electrons than a normal atom.



A normal atom (or a neutral atom) contains an equal number of protons and electrons. Now, since a

cation is formed by the loss of one or more electrons by an atom, therefore, a cation contains less

electrons than protons.

The ions of all the metal elements are cations. Only the hydrogen ion, H+, and ammonium ion, NH4+, are

the cations formed from non-metals.

Anions

A negatively charged ion is known as anion. Chloride ion, Cl–, and oxide ion, O2–, are anions because they

are negatively charged ions. An anion is formed by the gain of one or more electrons by an atom.

Cl

Chlorine atom

+ e–

Electron Cl–

Chloride ion

(An anion)

Since an anion is formed by the addition of electrons to an atom, therefore, an anion contains more

electrons than a normal atom. a normal atom (or a neutral atom) contains an equal number of protons

and electrons. Now, since an anion is formed by the addition of one or more electrons to an atom,

therefore, an anion contains more electrons than protons. The ions of all the non-metal elements are

anions (except hydrogen ion and ammonium ion).

Types of Chemical Bonds

There are two types of chemical bonds :

Ionic bonds are formed by the transfer of electrons from one atom to another

Covalent bonds are formed by the sharing of electrons between two atoms.

Ionic bond is also called electrovalent bond.

IONIC BOND

The chemical and formed by the transfer of electrons from one atom to another is known as an ionic

bond. The transfer of electrons takes place in such a way that the ions formed have the stable electron

arrangement of an inert gas. The ionic bond is called so because it is a chemical bond between

oppositely charged ions.

An ionic bond is formed when one of the atoms can donate electrons to achieve the inert gas electron

configuration, and the other atom needs electrons to achieve the inert gas electron configuration.

When a metal reacts with non-metal, transfer of electrons takes place from metal atoms to the non-metal

atoms, and an ionic bond is formed.

The strong force of attraction developed between the oppositely charged ions is known as an ionic bond.

Electron dot structures of metals and non metals

Ionic compounds are made up of ions.

Formation of Sodium Chloride



The formation of potassium chloride (KCl)

Formation of Magnesium Chloride

The formation of calcium chloride (CaCl2)

Formation of Magnesium Oxide.

PROPERTIES OF IONIC COMPOUNDS

1. Ionic compounds are usually crystalline solids. For example, sodium chloride is a crystalline solid.

2. Ionic compounds have high melting points and high boiling points for example, sodium chloride has a

high melting point of 800°C and a high boiling point of 1413°C.

3. Ionic compounds are usually soluble in water but insoluble in organic solvents (like either, acetone,

alcohol, benzene, kerosene, carbon disulphide and carbon tetrachloride). For example, sodium chloride is

soluble in water but insoluble in organic solvents like ether benzene or kerosene oil.

4. Ionic compounds conduct electricity when dissolved in water or when melted.



Why ionic compounds are solids?

The ionic compounds are solids because their oppositely charged ions attract one another strongly and form

a regular crystal structure.

Why ionic compounds have high melting and boiling points?

The ionic compounds are made up of positive and negative ions. There is a strong force of attraction

between the oppositely charged ions, so a lot of heat energy is required to break this force of attraction and

melt or boil the ionic compound. Due to this, ionic compounds have high melting points and high boiling

points.

Why ionic compounds dissolve in water but not in organic solvents?

The ionic compounds dissolve in water because water has a high dielectric constant due to which it weakens

the attraction between the ions.

Why ionic compounds conduct electricity in liquid form and melted form but not in solid form?

Or

Why ionic compounds are called electrolytes in solution form?

Ionic compounds conduct electricity because they contain charged particles called ions. although solid ionic

compounds are made up of ions but they do not conduct electric current in the solid state. This is due to the

fact that in the solid ionic compound, the ions are held together in fixed positions by strong electrostatic

forces and cannot move freely. so, solid ionic compounds are non conductors of electricity. When we

dissolve the ionic solid in water or melt it the crystal structure is broken down and ions become free to move

and conduct electricity. Thus, an aqueous solution of an ionic compound (or a molten ionic compound)

conducts electricity because there are plenty of free ions in the solution which are able to conduct electric

current.

This means that ionic compounds are electrolytes.

OCCURRENCE OF METALS

The earth’s crust is the major source of metals. Sea-water also contains salts of metals like sodium

chloride, magnesium chloride, etc. Most of the metals are quite reactive and hence they do not occur as

free elements in nature. So, most of the metals are found in the form of their compounds (with other

elements) called ‘combined state’. The compounds of metals found in nature are their oxides,

carbonates, sulphides and chlorides, etc. In these compounds, the metals are present in the form of

positive ions (or cations). Only a few less reactive metals (like copper, silver, gold and platinum) are

found in the ‘free state’ as metals.

Minerals and Ores

The natural materials in which the metals or their compounds are found in earth are called minerals.

Those minerals from which the metals can be extracted conveniently and profitable are called ores. An

ore contains a good percentage of metal and there are no objectionable impurities in it. Al the ores are

minerals, but all the minerals are not ores.

Metal (to be extracted) Name of Ore Name if compound in

Ore

Formula of Ore

1. Sodium

2. Aluminium

3. Manganese

4. Zinc

5. Iron

Rock salt

Bauxite

Pyrolusite

(i) Calamine

(ii) Zinc blende

Sodium chloride

Aluminium oxide

Manganese dioxide

Zinc carbonate

Zinc sulphate

NaCl

Al2O3. 2H2O

MnO2

ZnCO3

ZnS



6. Copper

7. Mercury

Haematite

(i) Cuprite

(ii) Copper glance

Cinnabar

Iron (III) oxide

Copper (I) oxide

Copper (I) sulphide

Mercury (II) sulphide

Fe2O3

Cu2O

Cu2S

HgS

EXTRACTION OF METALS

To obtain a metal from its ore is called the extraction of metal. The various processes involved in the

extraction of metals from their ores, and refining are known as metallurgy. The three major steps

involved in the extraction of a metal from its ore are :

(i) Concentration of ore (or Enrichment of ore),

(ii) Conversion of concentrated ore into metal, and

(iii) Refining (purification) of impure metal.

1. Concentration of Ore (or Enrichment of Ore)

Ore is an impure compound of a metal containing a large amount of sand and rocky material. the

unwanted impurities like sand, rocky material, earthy particles, limestone, mica, etc., present in an

ore are called gangue. Before extracting the metal from an ore, it is necessary to remove these

impurities (or gangue). The methods used for removing gangue from ore depend on some

difference in the physical properties or chemical properties of the ore and gangue.

2. Conversion of Concentrated Ore into Metal

For the purpose of extracting metals from the concentrated ores, we can group all the metals into

following three categories.

(i) Metals of high reactivity (or Highly reactive metals)

(ii) Metals of medium reactivity (or Moderately reactive metals)

(iii) Metals of low reactivity (or Less reactive metals)

The extraction of metal from its concentrated ore is essentially a process of reduction of the metal

compound present in the ore.

Extraction of Highly Reactive Metals

The highly reactive metals such as potassium, sodium, calcium, magnesium and aluminium are placed

high up in the reactivity series in its upper part.

The highly reactive metals are extracted by the electrolytic reduction of their molten chlorides or oxides..

Electrolytic reduction is brought about by passing electric current through the molten salt. This process

is called electrolysis (which means splitting by electricity). The highly reactive metals (which are placed

high up in the reactivity series) are extracted by the electrolysis of their molten chlorides or oxides.

During electrolysis, the negatively charged electrode (cathode) acts as a powerful reducing agent by

supplying electrons to reduce the metal ions into metal. During the electrolysis (or electrolytic

reduction) of molten salts, the metals are always produced at the cathode (negative electrode). This is

due to the fact that metal ions are always positively charged and get attracted to the negatively charged

electrode (cathode) when electricity is passed through the molten metal salt (Molten salt means melted

salt. Salts are melted by strong heating). The metals extracted by electrolysis method are very pure.

(i) When a molten metal chloride is electrolysed by passing electric current, then pure metal is

produced at the cathode (negative electrode) and chlorine gas is formed at the anode (positive

electrode).

(ii) When a molten metal oxide is electrolysed by passing electric current, then pure metal is produced

at the cathode (negative electrode) whereas oxygen gas is formed at the anode (positive electrode).

The highly reactive metals potassium, sodium, calcium, and magnesium are extracted by the electrolysis

of their molten chlorides whereas aluminium metal is extracted by the electrolysis of its molten oxide.



Extraction of Sodium Metal

2NaCl (1)

Sodium Chloride

(Molten)

Electrolysis 2 Na (s)

Sodium metal

+ Cl2 (g)

Chlorine gas

The positive sodium ions (Na+) are attracted to the cathode (negative electrode). The sodium ions take

electrons from the cathode and get reduced to form sodium atoms (or sodium metal) :

At cathode :

2Na+

Sodium ions

(From molten NaCl)

+ 2e

Electrons

(From cathode)

2Na

Sodium atoms

(sodium metal)

The negative chloride ions (Cl) are attracted to the anode (positive electrode). The chloride ions give

electrons to the anode and get oxidised to form chlorine gas :

At anode

2Cl

Chloride ions

(From molten NaCl)

2e

Electrons

(Given to anode)

Cl2

Chlorine gas

Thus, chlorine gas is formed at the anode (positive electrode).

Potassium metal is produced by the electrolysis of molten potassium chloride (KCl); Calciummetal

is obtained by the electrolysis of molten calcium chloride (CaCl2); and magnesium metal is

extracted by the electrolysis of molten magnesium chloride (MgCl2).

Extraction of Aluminium Metal

2 Al2O3 (1)

Aluminium oxide

(Molten)

Electrolysis 4Al (1)

Aluminium metal

+ 3O2 (g)

Oxygen

The formation of aluminium and oxygen by the electrolysis of molten aluminium oxide can be explained as

follows :



The positively charged aluminum ions (Al3+) are attracted to the cathode (negative electrode). the

aluminium ions accept electrons from the cathode and get reduced to form aluminium atoms (or aluminium

metal) :

At cathode

Al3+

Aluminium ion

(From molten Al2O3)

+ 3e

Electrons

(From cathode)

Al

Aluminium atom

(Aluminium metal)

The negatively charged oxide ions (O2) are attracted to the anode (positive electrode). The oxide ions give

electrons to the anode and get oxidised to form oxygen gas :

At anode :

2O2

(From molten Al2O3)

4e

Electrons

(Given to anode)

O2

Oxygen gas

Thus, oxygen gas is produced at the anode.

Extraction of Moderately Reactive Metals

The moderately reactive metals such as zinc, iron, tin and lead, etc., are placed in the middle of the

reactivity series. So, the extraction of moderately reactive metals means the extraction of metals which

are in the middle of reactivity series.

The moderately reactive metals which are in the middle of reactivity series are extracted by the

reduction of their oxides with carbon, aluminium, sodium or calcium.

The moderately reactive metals occur in nature as oxides but others occur as their carbonate or

sulphide ores. It is easier to obtain metals from their oxides (by reduction) than from carbonates or

sulphides. So, before reduction can be done, the ore must be converted into metal oxide which can then

be reduced. The concentrated ores can be converted into metal oxide by the process of calcination or

roasting.

Calcination is the process in which a carbonate ore is heated strongly in the absence of air to convert it

into metal oxide.

ZnCO3 (s)

Zinc carbonate

(Calamine ore)

Calcination ZnO (s)

Zinc oxide

+ CO2 (g)

Carbon dioxide

Roasting is the process in which a sulphide ore is strongly heated in the presence of air to convert it into

metal oxide.

2ZnS (s)

Zinc sulphide

(Zinc blende ore)

+ 3O2 (g)

Oxygen

(From air)

Roasting 2ZnO (s)

Zinc oxide

+ 2SO2 (g)

Sulphur

dioxide

Thus metal oxides (obtained by calcination or roasting or ores) are converted to the free metal by using

reducing agents like carbon, aluminium, sodium or calcium.

Reducing of Metal Oxide With Carbon. The oxides of comparatively less reactive metals like zinc, iron,

nickel, tin, lead and copper, are usually reduced by using carbon as the reducing agent. In the reduction

by carbon, the metal oxide is mixed with carbon (in the form of coke) and heated in a furnace. carbon

reduces themetal oxide to free metal.

Zinc Metal is extracted by the reduction of its oxide with carbon (or coke). Thus, when zinc oxide is

heated with carbon, zinc metal is produced.

ZnO (s)

Zinc oxide

+ C (s)

Carbon Zn (s)

Zinc metal

+ CO (g)

Carbon



(Reducing

agent)

monoxide

Iron metal is extracted from it oxide ore ‘hematite’ (Fe2O3) by reduction with carbon (in the form of

coke). Tin and lead metals are also extracted by the reduction of their oxides with carbon. Even the

less reactive metal copper is extracted by the reduction of its oxide with carbon.

Reduction of Metal Oxide With Aluminum. A more reactive metal like aluminium can also be used as

a reducing agent in the extraction of metals from their oxides. Aluminium is used as a reducing agent in

those cases where the metal oxide is of a comparatively more reactive metal than zinc, etc., which cannot

be satisfactorily reduced by carbon. This is because a more reactive metal (like aluminium) can displace

a comparatively less reactive metal from its metal oxide to give free metal.

Manganese and chromium metals are extracted by the reduction of their oxides with aluminium

powder.

Manganese metal is extracted by the reduction of its oxide with aluminium powder as the reducing

agent.

3MnO2 (s)

Manganese

Dioxide

+ 4Al (s)

Aluminium

powder

(Reducing

agent)

3Mn (1)

Manganese

Metal

+L 2Al2O3 (s)

Aluminium

oxide

+ Heat

The reduction of manganese dioxide with aluminium is a highly exothermic reaction. A lot of heat is

evolved during the reduction of manganese dioxide with aluminium powder because of which the

manganese metal produced is in the molten state (or liquid state). Please note that aluminium is an

expensive reducing agent as compared to carbon (coke).

Thermite Reaction – The reduction of a metal oxide to form metal by using aluminum powder as a

reducing agent is called a thermite reaction (or thermite process). The reaction of metal oxides with

aluminium powder to produce metals are highly exothermic in which a large amount of heat is evolved.

In fact, the amount of heat evolved is so large that the metals are produced in the molten state. This

property of the reduction by aluminium is made use of in thermite welding for joining the broken pieces

of heavy iron objects like girders, railway tracks or cracked machine parts.

Fe2O3 (s)

Iron (III) oxide

+ 2Al (s)

Aluminium powder

(Reducing agent)

2Fe (1)

Iron metal

(Molten state )

+

Heat

The molten iron is then poured between the broken iron pieces to weld them (to join them). This

process is called aluminothermy or thermite welding. Thus, thermite welding makes use of the reducing

property of aluminium.

Fraction of Less Reactive Metals

The less reactive metals which are quite low in the activity series are extracted by the reduction of their

oxides by heat alone. For example, mercury and copper are less reactive metals which are placed quite

low in the reactivity series. so, mercury and copper metals are extracted by the reduction of their

oxides by heat along.

Extraction of Mercury. Mercury is a less reactive metal which is quite low in the activity series.

Mercury metal can be extracted just by heating its sulphide ore in air. This happens as follows.

Mercury metal is produced from the sulphide are called cinnabar, HgS, which is actually mercury (II)

sulphide. The extraction of mercury from cinnabar ore involves the following two steps :

(a) The concentrated mercury (II) sulphide ore (cinnabar ore) is roasted in air when mercury (II) oxide is

formed.

2HgS (s) + 3O2 (g) Roasting 2HgO (s) + 2SO2 (g)



Mercury (II) sulphide

(Cinnabar ore)

Oxygen

(From air)

Mercury (II)

oxide

Sulphur dioxide

(b) When this mercury (II) oxide is heated to about 300°C, it decomposes (gets reduced) to form mercury

metal :

2HgO (s)

Mercury, (II) oxide

(From above)

Heat

(Reduction) 2Hg (1)

Mercury metal

+ O2 (g)

Oxygen

Extraction of copper

One of the ores from which copper metal is produced is copper glance, Cu2S, which is actually copper (I)

sulphide. The extraction of copper from copper glance ore involves the following two steps :

(a) The concentrated copper (I) sulphide ore (copper glance) is roasted in air when a part of copper (I)

sulphide is oxidised to copper (I) oxide :

2Cu2 S (s)

Copper (I)

Sulphide

(Copper glance

ore)

+ 3 O2 (g)

Oxygen

(From air)

Roasting 2Cu2O (s)

Copper (I)

oxide

+ 2SO2 (g)

Sulphur dioxide

(b) When a good amount of copper (I) sulphide has been converted into copper (I) oxide, then the supply

of air for roasting is stopped. In the absence of air, copper (I)oxide formed above reacts with the remaining

copper (I) sulphide to form copper metal and sulphur dioxide :

2Cu2 S (s)

Copper (I)

oxide

(Formed above

+ Cu2S (s)

Copper (I) sulphide

(From unoxidised ore)

Heat 6Cu (s)

Copper metal

+ SO2 (g)

Sulphur dioxide

Refining of metals

The metals prepared by the various reduction processes usually contain some impurities, so they are

impure. The process of purifying impure metals is called refining of metals.

The most important and most widely used method for refining impure metals is electrolytic refining.

Electrolytic Refining. Electrolytic refining means refining by electrolysis. Many metals like copper, zinc,

tin, lead, chromium, nickel, silver and gold are refined electrolytically.

(a) A thick block of the impure metal is made anode (It is connected to the positive terminal of the battery.

(b) A thin strip of the pure metal is made cathode (It is connected to the negative terminal of the battery)

(c) A water soluble salt (of the metal to be refined) is taken as electrolyte.

On passing electric current, impure metal dissolves from the anode and goes into the electrolyte solution.

And pure metal from the electrolyte deposit on the cathode. The soluble impurities present in the impure

metal go into the solution whereas the insoluble impurities settle down at the bottom of the anode as ‘anode

mud’.

Electrolytic Refining of Copper.



The apparatus consists of an electrolytic tank containing acidified copper sulphate solution as electrolyte

(The copper sulphate solution is acidified with dilute sulphuric acid). A thick block of impure copper metal

is made anode. (it is connected to the +ve terminal of the battery), and a thin strip of pure copper metal is

made cathode. (It is connected to theve terminal of the battery).

On passing electric current, impure copper from anode dissolves and goes into copper sulphate solution, and

pure copper from the copper sulphate solution deposits on cathode. Thus, pure copper metal is produced on

the cathode. The soluble impurities go into the solution whereas insoluble impurities collect below the

anode as anode mud.

At cathode

Cu2+

Copper ion

(From

electrolyte)

+ 2e

Electrons

(From cathode)

Cu

Copper atom

(Deposits on

cathode)

At anode :

Cu

Copper atom

(from impure anode)

2e

Electrons

(Given to anode)

Cu2+

Copper ion

(Goes into electrolyte)

Gold and silver metals can be recovered from the anode mud. The electrolytic refining of metals

serves two purposes.

(i) It refines (purifies) the metal concerned.

(ii) It enables to recover other valuable metals (like gold and silver) present as impurities in the

metal being refined.

CORROSION

The eating up of metals by the action of air, moisture or a chemical (such as an acid) on their

surface is called corrosion.

Rusting of Iron

When an iron object is left in damp air (or water) for a considerable time, it gets covered with a red-

brown flaky substance called rust. This is called rusting of iron. During the rusting of iron, iron metal

combines with the oxygen of air in the presence of water to form hydrated iron (III) oxide, Fe2O3x2O.

This hydrated iron (III) oxide is called rust, So, rust is mainly hydrated iron (III) oxide, Fe2O3xH2O.

Rust is red brown in colour.

Conditions Necessary for the Rusting of Iron

1. Presence of air (or oxygen)

2. Presence of water (or moisture)

Damp air alone supplies both the things, air and water, required for the rusting of ion. Again ordinary water

has always some air dissolved in it. So, ordinary water alone also supplies both the things, air and water,

needed for rusting.

Prevention of Rusting



1. Rusting of iron can be prevented by painting. (When a coat of paint is applied to the surface of a iron

object, then air and moisture cannot come in contact with the iron object and hence no rusting takes place.)

The iron articles such as window grills, railings, steel furniture, iron pipes, iron bridges, railway coaches,

ships, and bodies of cars, buses and trucks, etc., are all painted to protect them from rusting.

2. Rusting of iron can be prevented by applying grease or oil. (When some grease or oil is applied to the

surface of an iron object, then air and moisture cannot come in contact with it and hence rusting is

prevented. ) The tools and machine parts made of iron and steel are smeared with tease or oil to prevent

their rusting.

3. Rusting of iron can be prevented by galvanisation. ( The process of depositing a thin layer of zinc metal

on iron objects is called galvanisation. Galvanisation is done by dipping an iron object in molten zinc metal.

A thin layer of zinc metal is then formed all over the iron object. This thin layer of zinc metal on the surface

of iron objects protects them from rusting.) The iron sheets used for making buckets, drums, dust-bins and

sheds (roofs) are galvanised to prevent their rusting.

How a more reactive metal zinc is able to protect iron from rusting. Zinc is a quite reactive metal. The

action of air on zinc metal forms a very thin coating of zinc oxide all over it. This zinc oxide coating is hard

and impervious to air and hence prevents the further corrosion of zinc metal (because air is not able to pass

through this hard zinc oxide coating. So, when a layer of zinc metal is deposited on an iron object, then the

zinc oxide coating formed on its surface protects the zinc metal of zinc layer as well as the iron below it.

Please note that the galvanised iron object remains protected against rusting even if a break occurs in the

zinc layer. This is because zinc is more easily oxidised then iron. So, when zinc layer on the surface of

galvanised iron object is broken, then zinc continues to corrode but iron object does not corrode or rust.

4. Rusting of iron can be prevented by tin-plating and chromium-plating. (Tin and chromium metals are

resistant to corrosion. So, when a thin layer of tin metal (or chromium metal) is deposited on iron and steel

objects by electroplating, then the iron and steel objects are protected from rusting.) For example, tiffin-

boxes made of steel are nickel-plated from inside and outside to protect them from rusting. Tin is used for

plating tiffin-boxes because it is non-poisonous and hence does not contaminate the food kept in them.

Chromoun-plating is done on taps, bicycle handle bars and car bumpers made f iron and steel to protect

them from rusting and give them a shiny appearance.

5. Rusting of iron can be prevented by allowing it to make stainless steel. (When iron is alloyed with

chromoum and nickel, then stainless steel is obtained. Stainless steel does not rust at all.) Cooking utensils,

knives, scissors and surgical instruments, etc. are made of stainless steel and do not rust at all. But stainless

steel is too expensive to be used in large amounts.

Corrosion of Aluminium

Due to the formation of dull layer of aluminium oxide on exposure to moist air, the aluminium vessel

loses its shine very soon after use.

The action of moist air on aluminium metal forms a thin layer of aluminium oxide all over the aluminium

metal. This aluminium oxide layer is very tough and prevents the metal underneath from further

corrosion (because moist air is not able to pass through this aluminium oxide layer). In this way, a thin

aluminium oxide layer formed on the surface of aluminium objects protects them from further corrosion.

This mean that sometimes corrosion is useful. Because a newly cut piece of almuminium metal corrodes

quickly to form a strong layer of aluminium oxide on its surface which then protects the aluminium piece

from further corrosion.

Anodising:



The layer of aluminium oxide on the surface of aluminium objects can be made thicker by electrolysis (to

give them even more protection from corrosion). This process is called anodising. In this process, the

aluminium object is made an anode (positive electrode) in an electrolytic tank in which dilute sulphuric

acid is electrolysed. During the electrolysis of dilute sulphuric acid, oxygen gas is liberated at the anode

and reacts with the aluminium object to form a thicker layer of aluminium oxide layer protects the

aluminium object from corrosion very effectively.

Corrosion of Copper

A copper object remains in damp air for a considerable time, then copper reacts slowly with the carbon

dioxide and water of air to form a green coating of basic copper carbonate on the surface of the object.

The green coating of basic copper carbonate is a mixture of copper carbonate and copper hydroxide,

CuCO3. Cu(OH)2.

The corroded copper vessel can be cleaned with dilute acid solution. The acid solution dissolves green

coloured basic copper carbonate present on the corroded copper vessels and makes them look shiny,

red-brown again

Corrosion of Silver

Silver ornaments (and other silver articles) gradually turn black due to the formation of a thin silver

sulphide layer on their surface by the action of hydrogen sulphide gas present in air.

Silver is a bright, shiny metal which is chemically quite un-reactive. Silver metal loses its shine and

becomes dull (or tarnished) very slowly. Thus, silver metal is fairly resistant to corrosion. Silver metal is

used to make silver coins, jewellery and silverware (such as silver utensils and decorative articles)

because of its bright shiny surface and resistance of corrosion,

The case of Gold and Platinum

Since gold does not corrode, therefore, gold ornaments look new even after several years of use.

Gold id used to make jewellery because of its bright shiny surface and high resistance to corrosion.

Platinum is another metal which is highly resistant to corrosion. Platinum is used to make jewellery

because of its bright shiny surface and high resistance to corrosion.

ALLOYS

An alloy is a homogeneous mixtures of two or more metals (or a metal and small amounts of non-

metals). For example, brass in an alloy of two metals : copper and zinc, whereas steel is an alloy of a

metal and a small amount of a non-metal : iron and carbon. An alloy is prepared by mixing the various

metals in molten state in required proportions, and then cooling their mixture to the room temperature.

The properties of an alloy are different from the properties of the constituent metals (from which it is

made)

1. Alloys are stronger than the metals from which they are made.

2. Alloys are harder than the constituent metals.

3. Alloys are more resistant to corrosion.

4. Alloys have lower melting points than the constituent metals.



5. Alloys have lower electrical conductivity than pure metals.

Some of the common alloys are:

Duralumin or Duralium, Magnalium, Steel, Stainless steel, Brass, Bronze, Solder and Amalgams.

Brass:

Brass is an alloy of copper and Zinc (Cu and Zn). It contains 80% copper and 20% zinc. Brass is more

malleable and more strong then pure copper. Its colour is also more golden. Brass is used for making

cooking utensils, screws, nuts, bolts, wires, tubes, scientific instruments like microscopes and ornaments.

Brass is also sed for making vessels like flower vases and fitting like that of fancy lamps.

Bronze :

Bronze is an alloy of Copper and Tin (Cu and Sn). It contains 90% copper and 10% tin. Bronze is very

tough and highly resistant to corrosion. It is used for making statues, coins, medals, cooking utensils and

ship’s propellers.

The electrical conductivity or an alloy is less than that of pure metals. For example, brass (an alloy of

copper and zinc) and bronze (an alloy of copper and tin) are not good conductors of electricity but pure

copper is an excellent conductor of electricity and used for making electrical circuits.

Solder :

Solder is an alloy of lead and tin (Pb and Sn). It contains 50% lead and 50% tin. The melting point of an

alloy is less than that of pure metals. Solder is an alloy which has now melting point. So, it is used for

soldering (or welding) electrical wires together.

Amalgam :

An alloy of mercury metal with one or more other metals is knows as an amalgam. A solution of sodium

metal in liquid mercury metal is called sodium amalgam. An amalgam consisting of mercury, silver, tin

and zinc is used by dentists for fillings in teeth.

Alloys of Gold:

The purity of gold is expressed in terms of ‘carats’. Pure gold is said to be of 24 carats. Pure gold (known

as 24 carat gold) is very soft due to which it is not suitable for making jewellery. Gold is alloyed with a

small amount of silver or copper to make it hard. This harder alloy of gold is more suitable for making

ornaments (because it becomes easier to work with it). In Indian, gold ornaments are usually made of 22

carat gold. It metals that 22 pars pure gold is alloyed with 2 parts of either silver or copper for making

ornaments. Thus, 22 carat gold is an alloy of gold with silver or copper.

The Iron Pillar at Delhi

The iron pillar near Qutab Minar in Delhi is made up of wrought iron (which is a low-carbon steel). This

iron pillar was made around 400 BC by the Indian iron workers. Tough wrought iron rusts slowly with

time but the Indian iron workers had developed a process which prevented the wrought iron pillar from

rusting even after thousands of years! The rusting has been prevented because of the formation of a thin

film of magnetic oxide of iron (Fe3O4) on the surface as a result of finishing treatment given to the pillar,

painting it with a mixture of different salts, then heating and quenching (rapid cooling). The iron pillar is

8 meters high and 6000 kg (6 tonnes) in weight. This iron pillar stands in good condition more than

2000 years after it was made.



All the plants and animals (including human beings) are alive or living thing. The most important criterion to decide whether something is alive (or not) is the movement.

Movement is one of the most important signs of life in an organism. All the living things (which are alive) move by themselves without any external help. The movements

in most of the animals are fast and can be observed easily but the movements in plants are usually slow and observed with difficulty.

Animals can move from one place to another or they can move their body parts. For example, a frog moves when it jumps into a pond, a bird moves when it flies in the sky, an athlete moves when he runs and a fish moves when it swims in water.

The plants are fixed in the soil at a place, so they cannot move like animals from place to place. The plants can only move parts of their body such as leaves, flowers, shoots and roots. The plant parts move towards a stimulus such as sunlight, gravity or water etc. For example, the shoot, the leaves and flower of a sunflower plant move by bending towards the sun so as to face the sunlight.

Non-living things (which are not alive) cannot move by themselves. For example, a stone is a non-living thing which cannot move by itself from one place to another or show any other type of movement.

The movements over very small scale (as those in the molecules of living things) are invisible to the naked eye. The invisible molecular movement is, however, necessary for the existence of life.

In fact, viruses do not show any molecular movement in them (until they infect some cell) and this has created controversy about whether they are truly alive or not.

The characteristics of living things (i) Living things can move by themselves. (ii) Living things need food, air and water. (iii) Living things can grow. (iv) Living things can respond to changes around them. They are sensitive. (v) Living things respire (release energy from food). (vi) Living things excrete (get rid of waste materials from their body). (vii) Living things can reproduce. They can have young ones.

What are Life Processes

Life processes



The basic functions performed by living organisms to maintain their life on this earth are called life processes.

The basic life processes common to all the living organisms are: Nutrition and Respiration; Transport and Excretion; Control and Coordination (Response to stimuli); Growth; Movement and Reproduction.

The process of nutrition involves the taking of food inside the body and converting it into smaller molecules which can be absorbed by the body.

Respiration is the process which releases energy from the food absorbed by the body. Transport is the process in which a substance absorbed or made in one part of the body is moved to

other parts of the body. Excretion is the process in which the waste materials produced in the cells of the body are removed

from the body. Control and coordination (or response to stimuli) is a process which helps the living organisms to

survive in the changing environment around them. The process of growth involves the change from a small organism to a big organism (or an adult

organism). In movement, the organism either moves from one place to another or moves its body parts while

remaining at the same place. The process of reproduction involves the making of more organisms from the existing ones, so that

organisms could live on this earth forever. Energy is Needed for the Life Processes Food is a kind of fuel which provides energy to all the living organisms. The living organisms use the

chemical energy for carrying out various life processes. They get this chemical energy from food through chemical reaction.

The energy required by an organism comes from the food that the organism eats. Thus, food is the basic requirement of all the living organisms for obtaining energy.

NUTRITION Food is an organic substance. The simplest food is glucose. It is also called simple sugar. A more

complex food is starch. Starch is made from glucose. The general name of substances like glucose (sugar) and starch is ‘carbohydrates’.

Carbohydrates are the most common foods for getting energy. Fats and proteins are also foods. (A wider definition of food, however, also includes mineral salts, vitamins and water which are essential for the normal growth and development of an organism).

A nutrient is an organic or inorganic substance required for the maintenance of life and survival of a living organism.

A nutrient can be defined as a substance which an organism obtains from its surroundings and uses it as a source of energy or for the biosynthesis of its body constituents (like tissues and organs). For example, carbohydrates and fats are the nutrients which are used by an organism mainly as a source of energy whereas proteins and mineral salts are nutrients used by an organism for the biosynthesis of its body constituents like skin, blood, etc.

Nutrition is a process of intake of nutrients (like carbohydrates, fats, proteins, minerals, vitamins and water) by an organism as well as the utilisation of these nutrients by the organism.

Modes of Nutrition Modes of nutrition, means the methods of procuring food or obtaining food by an organism. There are mainly two modes nutrition

Autotrophic



Heterotrophic Autotrophic Mode of Nutrition Autotrophic nutrition is that mode of nutrition in which an organism makes (or synthesizes) its own

food from the simple inorganic materials like carbon dioxide and water present in the surroundings (with the help of sunlight energy.

The green plants have an autotrophic mode of nutrition. The autotrophic bacteria also obtain their food by the autotrophic mode of nutrition.

Carbon dioxide and water are inorganic substances. Those organisms which can make their own food from the inorganic substances present in the environment are called autotrophs.

All the green plants are autotrophs (because they can make their own food from inorganic substances like carbon dioxide and water present in the environment). Non-green plants are, however, not autotrophs. Certain bacteria called ‘autotrophic bacteria’ are also autotrophs.

The autotrophic organisms (or autotrophs) contain the green pigment called chlorophyll which is capable of trapping sunlight energy. This trapped sunlight energy is utilised by the autotrophs to make food by combining inorganic materials like carbon dioxide and water present in the environment by the process of photosynthesis.

Autotrophs make their own food by photosynthesis. So, autotrophs are the producers of food. Heterotrophic Mode of Nutrition Heterotrophic nutrition is that mode of nutrition in which an organism cannot make (or synthesize)

its own food from simple inorganic materials like carbon dioxide and water, and depends on other organisms for its food.

All the animals have a heterotrophic mode of nutrition. Most bacteria and fungi also have heterotrophic mode of nutrition.

Those organisms which cannot make their own food from inorganic substances like carbon dioxide and water, and depend on other organisms for their food are called heterotrophs.

All the animals are heterotrophs (because they cannot make food from inorganic substances like carbon dioxide and water and obtain their food from other plants or animals.). Thus, man, dog, cat, deer, tiger, bear, lion, cow, etc., are all heterotrophs. The non-green plants (like yeast) are also heterotrophs.

Types of Heterotrophic Nutrition The heterotrophic mode of nutrition is of three types:

Saprotrophic nutrition or saprophytic nutrition Parasitic nutrition Holozoic nutrition.

Saprotrophic Nutrition (or Saprophytic Nutrition) Saprotrophic nutrition is that nutrition in which an organism obtains its food from decaying organic

matter of dead plants, dead animals and rotten bread, etc. ‘Sapro’ means ‘rotten’, so a saprotrophic organism draws its food from rotting wood of dead and

decaying trees, rotten leaves, dead animals and household wastes like rotten bread etc. Saprophytes are the organisms which obtain their food from dead plants (like rotten leaves), dead

and, decaying animal bodies, and other decaying organic matter (like rotten bread). Fungi (like bread moulds, mushrooms, yeast), and many bacteria are saprophytes.

Fungi and bacteria are a kind of plants. So, we can also say that saprophytes are the plants which feed on dead and decaying organic matter.



The saprophytes break down the complex organic molecules present in dead and decaying matter and convert them into simpler substances outside their body. These simpler substances are then absorbed by saprophytes as their food.

Parasitic Nutrition The parasitic nutrition is that nutrition in which an organism derives its food from the body of

another living organism (called its host) without killing it. The organism which obtains the food is called a ‘parasite’, and the organism from whose body food is obtained is called the host.

A parasite receives its food from the host but gives no benefit to the host in return. A parasite usually harms the host. The host may be a plant or an animal.

Most of the diseases which affect mankind, his domestic animals (like dogs and cattle) and his crops are caused by parasitic mode of nutrition observed in several fungi, bacteria, a few plants like Cuscuta (amarbel) and some animals like Plasmodium and roundworms. Thus, the micro-organism ‘Plasmodium’ (which causes malaria disease) is a parasite.

Roundworm which causes diseases in man and domestic animals (like dogs and cattle) is also a parasite. Roundworms live inside the body of man and his domestic animals. Several fungi and bacteria, and plants like Cuscuta (amarbel) are also parasites. Some other examples of parasites are ticks, lice, leeches and tapeworms.

Holozoic Nutrition The holozoic nutrition is that nutrition in which an organism takes the complex organic food

materials into its body by the process of ingestion, the ingested food is digested and then absorbed into the body cells of the organism. The undigested and unabsorbed part of the food is thrown out of the body of the organism by the process of egestion.

Man, cat, dog; cattle, deer, tiger, lion, bear, giraffe, frog, fish and Amoeba, etc., have the holozoic mode of nutrition.

NUTRITION IN PLANTS Green plants are autotrophic and synthesize their own food by the process of photosynthesis.

‘Photo’ means ‘light’ and ‘synthesis’ means ‘to build’, thus ‘photosynthesis’ means ‘building up by light. The plants use the energy in sunlight to prepare food from carbon dioxide and water in the presence of chlorophyll. Chlorophyll is present in the green coloured bodies called ‘chloroplasts’ inside the plant cells. In fact, the leaves of a plant are green because they contain tiny green coloured organelles called chloroplasts (which contain chlorophyll).

The process, by which green plants make their own food (like glucose) from carbon dioxide and water by using sunlight energy in the presence of chlorophyll, is called photosynthesis. Oxygen gas is released during photosynthesis.

6CO2 Carbon dioxide

(from air)

+ 6H2O Water

(from soil)

+ Light energy

Chlorophyll (photosynthesis)

C6 H12 O6 Glucose (as food)

+ 6O2 Oxygen

Photosynthesis The process of photosynthesis takes place in the green leaves of a plant. In other words, food is

made in the green leaves of the plant.



The green leaves of a plant make the food by combining carbon dioxide and water in the presence of sunlight and chlorophyll.

The carbon dioxide gas required for making food is taken by the plant leaves from the air. This carbon dioxide enters the leaves through tiny pores in them called stomata.

Water required for making food is taken from the soil. This water is transported to the leaves from the soil through the roots and stem.

The sunlight provides energy required to carry out the chemical reactions involved in the preparation of food.

The green pigment called chlorophyll present in green leaves helps in absorbing energy from sunlight.

Oxygen gas is produced as a by-product during the preparation of food by photosynthesis. This oxygen gas goes into the air.

The food prepared by the green leaves of a plant is in the form of a simple sugar called glucose. This glucose food made in the leaves is then sent to the different parts of the plants.

The extra glucose is changed into another food called starch. This starch is stored in the leaves of the plant.

Glucose and starch belong to a category of foods called carbohydrates. The foods like carbohydrates prepared by photosynthesis contain chemical energy stored in them.

The food prepared by photosynthesis provides all the energy to a plant which it needs to grow. And when we eat plant foods (like food grains, fruits and vegetables), the chemical energy stored in them is released in our body during respiration.

The photosynthesis takes place in the following three steps:

(i) Absorption of sunlight energy by chlorophyll. (ii) Conversion of light energy into chemical energy, and splitting of water into hydrogen and oxygen

by light energy. (iii) Reduction of carbon dioxide by hydrogen to form carbohydrate like glucose by utilizing the

chemical energy (obtained by the transformation of light energy). The three steps involved in photosynthesis need not take place one after the other immediately.

Desert plants take up carbon dioxide at night and prepare an intermediate product which is acted upon by the sunlight energy absorbed by chlorophyll when the sun shines during the next day.

Conditions Necessary for Photosynthesis 1. Sunlight, 2. Chlorophyll, 3. Carbon dioxide, and 4. Water. The experiments on photosynthesis depend on

the fact that green leaves make starch as food. And that starch gives a blue-black colour with iodine solution. We should destarch the leaves of a plant before using it in a photosynthesis experiment. The green leaves of a plant are destarched by keeping this plant in a completely dark place in a room for at least three days.



When the plant is kept in a dark place, it cannot make more starch (food) by photosynthesis because there is no sunlight. So, the plant kept in dark place uses the starch already stored in its leaves during respiration. The plant will use up all the starch stored in its leaves in about three days’ time.

Raw Materials for Photosynthesis The raw materials for photosynthesis are: (i) Carbon dioxide, and (ii) Water. How the Plants Obtain Carbon Dioxide There are a large number of tiny pores called stomata on the surface of the leaves of plants (The

singular of stomata is stoma). The green plants take carbon dioxide from air for photosynthesis. The carbon dioxide gas enters the leaves of the plant through the stomata present on their surface.

Each stomatal pore (or stoma) is surrounded by a pair of guard cells. The opening and closing of stomatal pores is controlled by the guard cells. When water flows into

the guard cells, they swell, become curved and cause the pore to open. On the other hand, when the guard cells lose water, they shrink, become straight and close the stomatal pore.

A large amount of water is also lost from the cells of the plant leaves through open stomatal pores. So, when the plant does not need carbon dioxide and wants to conserve water, the stomatal pores are closed.

The oxygen gas produced during photosynthesis also goes out through the stomatal pores of the leaves.

The green stems (or shoots) of a plant also carry out photosynthesis. Stomata allow the movement of gases in and out of plant cell.

The gaseous exchange in plants takes place through the stomata in leaves (and other green parts). In most broad-leaved plants, the stomata occur only in the lower surface of the leaf but in narrow-

leaved plants, the stomata are equally distributed on both the sides of the leaf. The aquatic plants (or water plants) use the carbon dioxide gas dissolved in water for carrying out photosynthesis.

How the Plants Obtain Water for Photosynthesis The water required by the plants for photosynthesis is absorbed by the roots of the plants from the

soil through the process of osmosis. The water absorbed by the roots of the plants is transported upward through the xylem vessels to

the leaves where it reaches the photosynthetic cells and utilised in photosynthesis. The plants take materials like nitrogen, phosphorus, iron and magnesium, etc., from the soil. For

example, nitrogen is an essential element used by the plants to make proteins and other compounds.

The plants take up nitrogen from the soil in the form of inorganic salts called nitrates (or nitrites), or in the form of organic compounds which are produced by bacteria from the atmospheric.



Site of Photosynthesis: Chloroplasts Chloroplasts are the organelles in the cells of green plants which contain chlorophyll and where

photosynthesis takes place. Photosynthesis occurs in the organelles called chloroplasts present in the photosynthetic cells (or mesophyll cells) of green plants. The sites of photosynthesis in a cell of the leaf are chloroplasts.

A typical photosynthetic cell (or mesophyll cell) of a green leaf may contain 100 or more tiny chloroplasts in it, and a whole leaf may contain many thousands of photosynthetic cells.

Carbon dioxide needed for photosynthesis enters from the air into the Leaf through the stomata in its surface and then diffuses into the mesophyll cells and reaches the chloroplasts. Water is carried to the leaf by xylem vessels and passes into the mesophyll cells by diffusion and reaches the chloroplasts.

There is a thin, waxy protective layer called cuticle above and below a leaf which helps to reduce the loss of water from the leaf.

NUTRITION IN ANIMAL Animals Obtain their Food from Plants or Other Animals All the animals can be divided into three groups on the basis of their food habits (or eating habits) These are: (i) Herbivores, (ii) Carnivores, and (iii) Omnivores. 1. Herbivores Those animals which eat only plants

are called herbivores. The herbivores may eat grasses, leaves, grains, fruits or the bark of trees. Some of the examples of herbivores are Goat, Cow, Buffalo, Sheep, Horse, Deer, Camel, Ass, Ox,

Elephant, Monkey, Squirrel, Rabbit, Grasshopper and Hippopotamus. Herbivores are plant eaters. Herbivores are also called herbivorous animals.

2. Carnivores Those animals which eat only other animals as food are called carnivores. Carnivores eat only the meat (or flesh) of other animals. Those animals which eat only the meat (or flesh) of other animals are called carnivores. Carnivores are meat eaters. Carnivores are also called carnivorous animals.

3. Omnivores Those animals which eat both, plants and animals are called omnivores. Example: man, dog, crow,

sparrow, mynah, ant, etc. Omnivores are plant eaters as well as meat eaters. Omnivores are also called omnivorous animals. How can we say that all plant and animals get energy form sun? Plants use the energy of sun and prepare food by photosynthesis. The plants utilise this food for

maintaining their life. These plants (and their products) are also eaten up by herbivores and



omnivores as food. And the carnivores eat herbivores as food. In this way, it is the energy of the sun which provides food for plants, and animals (herbivores, carnivores and omnivores).

Different steps in the Process of Nutrition in animals. The process of obtaining food and then using it for obtaining energy, growth and repair of the body,

is called nutrition. Ingestion, Digestion, Absorption, Assimilation and Egestion. Ingestion The process of taking food into the body is called ingestion. In most simple terms, ingestion means

‘eating of food’ by the animal. When we put food into our mouth with hands, we are ingesting (the food)

Digestion The process in which the food containing large, insoluble molecules is broken down into small, water

soluble molecules (which can be absorbed by the body) is called digestion. Animals use both, physical and chemical methods for digesting (breaking up) the large food

molecules. Physical methods include chewing and grinding the food in mouth and chemical methods include the

addition of digestive juices (enzymes) to food by the body itself. Absorption After digestion the food molecules become small and soluble. The soluble food molecules can pass through the walls of our intestine and go into blood. The

process in which the digested food passes through the intestinal wall into blood stream is called absorption.

Assimilation Blood carries the absorbed food to all the parts of the body. The food then enters each and every

cell of the body where it is used for producing energy and for making materials for the growth and repair of the body.

The process in which the absorbed food is taken in by body cells and used for energy, growth and repair, is called assimilation.

Egestion A part of the food which we eat remains undigested (or insoluble) which cannot be used by the

body. The undigested part of the food is then removed from the body in the form of faeces when we go to toilet.

The process in which the undigested food is removed from the body is called egestion.

NUTRITION IN SIMPLE ANIMALS

NUTRITION IN AMOEBA Amoeba is a unicellular animal. Amoeba eats tiny (microscopic) plants and animals as food which

float in water in which it live mode of nutrition in Amoeba is holozoic. The process of obtaining food by Amoeba is called phagocytosis (‘Phagocytosis’ means ‘cell

feeding’).



Ingestion Amoeba has no mouth or a fixed place for the ingestion of food

(intake of food). Amoeba ingests food by using its pseudopodia. When a food particle comes near Amoeba, then Amoeba ingests this food particle by forming

temporary finger-like projections called pseudopodia around it. The food is engulfed with a little surrounding water to form a food vacuole inside the Amoeba. This food vacuole can be considered to be a ‘temporary stomach’ of Amoeba. Digestion In Amoeba, food is digested in the food vacuole by digestive enzymes. The enzymes from

surrounding cytoplasm enter into the food vacuole and break down the food into small and soluble molecules by chemical reactions.

Absorption The digested food present in the food vacuole of Amoeba is absorbed directly into the cytoplasm of

Amoeba cell by diffusion. The digested food just spreads out from the food vacuole into the whole of Amoeba cell. After absorption of food, the food vacuole disappears. Assimilation A part of the food absorbed in Amoeba cell is used to obtain energy through respiration. The remaining part of absorbed food is used to make the parts of Amoeba cell which lead to the

growth of Amoeba. On assimilating food Amoeba grows in size. Egestion Amoeba has no fixed place (like anus) for removing the undigested part of food. When a

considerable amount of undigested food collects inside Amoeba, then its cell membrane suddenly ruptures at any place and the undigested food is thrown out of the body of Amoeba.

Paramecium is also a tiny unicellular animal which lives in water. Paramecium uses its hair like structures called cilia to sweep the food particles from water and put them into its mouth. The Paramecium has thin, hair-like cilia all over its body. The cilia move back and forth rapidly in water. When the cilia present around the mouth region of Paramecium move back and forth, they sweep



the food particles present in water into the mouth of Paramecium. This is the first step in the nutrition of Paramecium which is called ingestion.

Rest of the steps of paramecium is similar to that of amoeba. Why amoeba or other unicellular organisms do not need blood circulatory system? Amoeba and other consists of only one small cell, it does not require blood system to carry the

digested food. The digested food just spreads out from the food vacuole into the whole of Amoeba cell.

NUTRITION IN COMPLEX MULTICELLULAR ANIMALS.

In the complex multicellular animals like man (humans), grasshopper, fish and frog, etc., all the processes involved in nutrition are performed by a combination of digestive organs. This combination of digestive organs is called digestive system.

A long tube running from mouth to anus of a human being (or other animals) in which digestion and absorption of food takes place is called alimentary canal. Alimentary canal is also called ‘gut’.

NUTRITION IN HUMAN BEINGS

(Human Digestive System) The various organs of the human digestive system in sequence are: Mouth, Oesophagus (or Food

pipe), Stomach, Small intestine and Large intestine. The glands which are associated with the human digestive system and form a part of the human

digestive system are: Salivary glands, Liver and Pancreas. The human alimentary canal which runs from mouth to anus is about 9 metres long tube. The ducts of various glands open into the alimentary canal and pour the secretions of the digestive

juices into the alimentary canal. Ingestion The human beings have a special organ for the ingestion of food. It is called mouth. So, in human

beings, food is ingested through the mouth. The food is put into the mouth with the help of hands. Digestion The digestion of food begins in the mouth itself. In fact, the digestion of food starts as soon as we

put food in our mouth. Digestion takes place in two parts: physical and chemical. Physical digestion: The mouth cavity (or buccal cavity) contains teeth, tongue, and salivary glands.

The teeth cut the food into small pieces, chew and grind it. So, the teeth help in physical digestion. Chemical digestion: The salivary glands help in chemical digestion by secreting enzymes. The salivary

glands in our mouth produce saliva. The human saliva contains an enzyme called salivary amylase which digests the starch present in food into sugar. Thus, the digestion of starch (carbohydrate) begins in the mouth itself. The food remains in the mouth only for a short time, so the digestion of food remains incomplete in mouth.

The slightly digested food in the mouth is swallowed by the tongue and goes down the food pipe called oesophagus. The oesophagus carries food to the stomach.

Digestion in stomach: The stomach is a J-shaped organ present on the left side of the abdomen. The food is further

digested in the stomach.



The food is churned in the stomach for about three hours. The food breaks down into still smaller pieces and forms a semi-solid paste.

The stomach wall contains three tubular glands in its walls. The glands present in the walls of the stomach secrete gastric juice.

The gastric juice contains three substances: hydrochloric acid, the enzyme pepsin and mucus.

The presence of hydrochloric acid, the gastric juice is acidic in nature. In the acidic medium, the enzyme pepsin begins the digestion of proteins present in food to form smaller molecules. Thus, the protein digestion begins in the stomach.

The protein digesting enzyme pepsin is active only in the presence of an acid. The partially digested food then goes from the stomach into the small intestine.

From the stomach, the partially digested food enters the small intestine: The small intestine is the largest part of the alimentary canal. It is about 6.5 metres long in an adult man. The small intestine is arranged in the form of a coil in our belly.

The small intestine in human beings is the site of complete digestion of food (like carbohydrates, proteins and fats). The small intestine receives the secretions of two glands: liver and pancreas.

Role of liver in digestion: Liver secretes bile. Bile is a greenish yellow liquid made in the liver which is normally stored

in the gall bladder. Bile is alkaline, and contains salts which help to emulsify or break the fats (or lipids) present

in the food. Bile performs two functions: (i) makes the acidic food coming from the stomach alkaline so

that pancreatic enzymes can act on it, and (ii) bile salts break the fats present in the food into small globules making it easy for the enzymes to act and digest them.

Role of pancreas in digestion: Pancreas is a large gland which lies parallel to and beneath the stomach secretes pancreatic

juice which contains digestive enzymes like pancreatic amylase, trypsin and lipase. The enzyme amylase breaks down the starch, the enzyme trypsin digests the proteins and

the enzyme lipase breaks down the emulsified fats. Role of small intestine in completion of digestion:

The walls of small intestine contain glands which secrete intestinal juice. The intestinal juice contains a number of enzymes which complete the digestion of complex

carbohydrates into glucose, proteins into amino acids and fats into fatty acids and glycerol. Glucose, amino acids, fatty acids and glycerol are small, water soluble molecules.

The process of digestion converts the large and insoluble food molecules into small, water soluble molecules. The chemical digestion of food is brought about by biological catalysts called enzymes.

Absorption



After digestion, the molecules of food become so small that they can pass through the walls of the small intestine (which contain blood capillaries) and go into our blood. This is called absorption.

The small intestine is the main region for the absorption of digested food. The large surface area of small intestine due to the presence of the finger like projections called villi, helps in the rapid absorption of digested food.

The digested food which is absorbed through the walls of the small intestine, goes into our blood. Assimilation The blood carries digested and dissolved food to all the parts of the body where it becomes

assimilated as part of the cells. This assimilated food is used by the body cells for obtaining energy as well as for growth and repair

of the body. The energy is released by the oxidation of assimilated food in the cells during respiration. Egestion A part of the food which we eat cannot be digested by our body. This undigested food cannot be

absorbed in the small intestine. The undigested food passes from the small intestine into a wider tube called large intestine. It is

called large intestine because it is a quite wide tube. The ‘walls of large intestine absorb most of the water from the undigested food (with the help of

villi). Due to this, the undigested part of food becomes almost solid. The last part of the large intestine called ‘rectum’ stores this undigested food for some time. And

when we go to the toilet, then this undigested food is passed out (or egested) from our body through anus as faeces or stool’.

The act of expelling the faeces is called egestion or defecation. The exit of faeces is controlled by the anal sphincter. Which glands produce saliva? What are the functions of saliva in mouth? The salivary glands in our mouth produce saliva. Our tongue helps in mixing this saliva with food. Saliva is a watery liquid so it wets the food in our

mouth. The wetted food can be swallowed more easily. The human saliva contains an enzyme called salivary amylase which digests the starch present in

food into sugar.

Watering of mouth Whenever we see any food then our mouth is always watered. Watering of mouth is due to the

production of saliva by the salivary glands in the mouth. Define peristaltic movements? What is the function of peristaltic movements? The walls of food pipe have muscles which can contract and expand alternately. When the slightly

digested food enters the food pipe, the walls of food pipe start contraction and expansion movements. The contraction and expansion movement of the walls of food pipe is called peristaltic movement.

This peristaltic movement of food pipe (or oesophagus) pushes the slightly digested food into the stomach the peristaltic movement moves the food in all the digestive organs throughout the alimentary canal.



What are the functions of hydrochloric acid in stomach? The hydrochloric acid provides the acidic medium for the action of enzyme pepsin to partly digest

the proteins present in the food. Hydrochloric acid is that it kills any bacteria which may enter the stomach with food. What is the function of mucus in stomach? What will happen if mucus is not secreted in the gastric juice? The mucus helps to protect the stomach wall from its own secretions of hydrochloric acid. If mucus is not secreted, hydrochloric acid will cause the erosion of inner lining of stomach leading to

the formation of ulcers in the stomach. Name the muscles which controls the amount of food released from stomach to small intestine? The exit of food from stomach is regulated by contraction and expansion movements of ‘sphincter

muscle’ which releases it in small amounts into the small intestine. Why small intestine is called small intestine? How it is arranged in our belly? Though the small intestine is very long, it is called small intestine because it is very narrow. The small intestine is arranged in the form of a coil in our belly. Why the length of small intestine differs in various animals? The length of the small intestine differs in various animals depending on the type of food they eat. Cellulose is a carbohydrate food which is digested with difficulty. So, the herbivorous animals like

cow which eat grass need a longer ‘small intestine’ to allow the cellulose present in grass to be digested completely.

Meat is a food which is easier to digest. So, the carnivorous animals like tigers which eat meat have a shorter ‘small intestine’.

How small intestine is adapted to absorb the digested food? The small intestine is especially adapted for absorbing the digested food. The inner surface of small

intestine has millions of tiny, finger- like projections called villi. The presence of villi gives the inner walls of the small intestine a very large surface area.

What happens to the digested food which is not immediately used by our body? The digested food which is not used by our body immediately is stored in the liver in the form of a

carbohydrate called ‘glycogen’. This stored glycogen can be used as a source of energy by the body as and when required.

Structure of tooth The hard, outer covering of a tooth is called enamel. Tooth enamel is the hardest material in our body. It is harder than

even bones. The part of tooth below enamel is called dentine. Dentine is similar

to bone. Inside the dentine is pulp cavity. The pulp cavity contains nerves and

blood vessels. Dental Caries



The formation of small cavities (or holes) in the teeth due to the action of acid-forming bacteria and improper dental care is called dental caries.

How dental caries are caused? If the teeth are not cleaned regularly, they become covered with a sticky, yellowish layer of food

particles and bacteria cells called ‘dental plaque’. Since plaque covers the teeth forming a layer over them, the alkaline saliva cannot reach the tooth surface to neutralise the acid formed by bacteria and hence tooth decay sets in.

How dental caries affects our tooth and cause pain? When we eat sugary food, the bacteria in our mouth act on sugar to produce acids. These acids first

dissolve the calcium salts from the tooth enamel and then from dentine forming small cavities (or holes) in the tooth over a period of time.

The formation of cavities reduces the distance between the outside of the tooth and the pulp cavity which contains nerves and blood vessels.

The acids produced by bacteria irritate the nerve endings inside the tooth and cause toothache. If the cavities caused by dental decay are not cleaned and filled by a dentist, the bacteria will get into

the pulp cavity of tooth causing inflammation and infection leading to severe pain. How can we reduce the risk of dental caries? Brushing the teeth regularly, after eating food, removes the plaque before bacteria produces acids.

This will prevent dental caries or tooth decay.

RESPIRATION Purpose of assimilation: The assimilated food is used mainly for two purposes:

1. Assimilated food is used as a fuel to get energy for various life processes, and 2. Assimilated food is used as a material for the growth and repair of the body.

Food is the ‘fuel’ for energy production in cells. Why does living things need oxygen: Living things need oxygen (of air) to obtain energy from food.

This oxygen reacts with the food molecule (Iike glucose) present in the body cells and burns them slowly to release energy. The energy thus released is stored in ATP molecules in the cells. The body can use this stored energy whenever it wants to do so.

The process of releasing energy from food is called respiration. The process of respiration involves taking in oxygen (of air) into the cells, using it for releasing

energy by burning food, and then eliminating the waste products (carbon dioxide and water) from the body.

Food + Oxygen — Carbon dioxide + Water + Energy The process of respiration which releases energy takes place inside the cells of the body. So, it is also

known as cellular respiration. The process of cellular respiration is common to all the living organisms. It provides energy to the

cells. There are two by-products of cellular respiration: carbon dioxide and Water. Only carbon dioxide is considered the real waste product of respiration because its accumulation in

the body is harmful to the organism. Water produced during respiration is not harmful to the body. It is rather beneficial for the body.

Respiration is essential for life because it provides energy for carrying out all the life processes which are necessary to keep the organisms alive.



Breathing and Respiration The mechanism by which organisms obtain oxygen from the air and release carbon dioxide is called

breathing. Respiration is a more complex process. Respiration includes breathing as well as the oxidation of food in the cells of the organism to release energy.

Breathing is a physical process whereas respiration also includes biochemical process of oxidation of food.

The process of breathing involves the lungs of the organism whereas the process of respiration also involves the mitochondria in the cells where food is oxidized to release energy.

Purpose of respiration The main purpose of respiration is the release of energy from the oxidation of simple food molecules

like glucose. Respiration is just opposite of photosynthesis because photosynthesis makes food (like glucose) by

using carbon dioxide, water and sunlight energy, and releasing oxygen; whereas respiration breaks food (like glucose) by using oxygen, and releasing carbon dioxide, water and energy.

How Energy Released during Respiration is Stored The energy produced during respiration is stored in the form of ATP molecules in the

cells of the body and used by the organism as and when required. ADP is a substance called Adenosine Di-Phosphate. The molecules of ADP are present in a cell. ADP

has low energy content. ATP is a substance called Adenosine Tri-Phosphate. It is also present inside a cell. ATP has high

energy content. Inorganic phosphate is a substance which contains a phosphate group made up of phosphorus and

oxygen. Inorganic phosphates are also present in a cell. (i) How energy is stored in our body: The energy released during respiration is used to make ATP

molecules from ADP and inorganic phosphate. ADP combines with inorganic phosphate by absorbing the energy released during respiration to form ATP molecules

ADP (low energy)

+ Phosphate + Energy (from respiration)

ATP (high

energy) (ii) How stored energy is released for use: When the cell needs energy, then ATP can be broken down

using water to release energy. ATP → ADP + Phosphate + Energy

(For use in cells) Uses of stored energy: The energy stored in ATP is used by the body cells for various purposes like

contraction of muscles, conduction of nerve impulses, synthesis of proteins, and many cells other activities related to the functioning of cells. ATP is known as the energy currency of cell.

An Important Discussion Glucose is C6H1206. It is a six carbon atom compound. It is the simple food which is oxidized in the

cells of organisms during respiration. The oxidation of glucose to pyruvic acid (or pyruvate) is called glycolysis. It occurs in the cytoplasm

of a cell and not in mitochondria. The oxidation of glucose to pyruvic acid does not require oxygen. One molecule of glucose on glycolysis produces two molecules of pyruvic acid (or pyruvate).

Pyruvic acid is a three carbon atom compound. It is also called pyruvate. The formula of pyruvic acid or pyruvate is CH3— C—COOH. It is a ketonic carboxylic acid.

II O The fate of pyruvate formed during respiration depends on whether oxygen is present in the cells or not. If oxygen is present in the cells, then pyruvate is completely oxidised to carbon dioxide and water, and a



lot of energy is produced (in the form of ATP) if, oxygen is not present in the cells (that is, in the absence of oxygen), pyruvate is converted to either ‘ethanol and carbon dioxide’ or ‘lactic acid’ depending on whether such a process is taking place in a plant cell or an animal cell. Lactic acid is also a three carbon atom compound. It is also called lactate. The formula of lactic acid

or lactate is CH3—CH—COOH. It is a hydroxyl carboxylic acid. I OH TYPES OF RESPIRATION Two types of respiration: aerobic respiration and anaerobic respiration. Aerobic Respiration The respiration which uses oxygen is called aerobic respiration. It is called aerobic respiration

because it uses air which contains oxygen (‘aerobic’ means ‘with air’). Process of aerobic respiration: In aerobic respiration, the glucose food is initially broken down into 2

molecules of pyruvic acid without using carbon dioxide in cytoplasm by the process of glycolysis. Glucose

(1 moloecule)

Glycolysis (in

cytoplasm)

Pyruvate (pyruvuic

acid) (2 molecules)

Oxygen (Kreb’s cycle) (in mitochondria)

6CO2 + 6H2

O + 38 ATP

Mitochondria are the sites of aerobic respiration in the cells. Thus, the complete breakdown of pyruvate to give carbon dioxide, water and energy takes place in mitochondria. Aerobic respiration produces a Considerable amount of energy for use by the organism which gets stored in the ATP molecules.

Examples: Most of the living organisms carry out aerobic respiration (by using oxygen of air). For example, humans (man), dogs, cats, lions, elephants, cows, buffaloes, goat, deer, birds, lizards, snakes, earthworms, frogs, fish, and insects (such as cockroach, grasshopper, houseflies, mosquitoes and ants, etc.) and most of the plants carry out aerobic respiration by using oxygen of air (to obtain energy).

Anaerobic Respiration The respiration which takes place without oxygen is called anaerobic respiration. Why it is called anaerobic: It is called anaerobic respiration because it takes place without air which

contains oxygen (‘anaerobic’ means ‘without air’). Anaerobic respiration in non green plants (yeast): The microscopic organisms like yeast and some

bacteria obtain energy by anaerobic respiration (which is called fermentation). In anaerobic respiration, the micro-organisms like yeast break down glucose (food) into ethanol and carbon dioxide, and release energy.

Glucose (1

moloecule)

Glycolysis (in

cytoplasm)

Pyruvate (pyruvuic

acid) (2 molecules)

In the absence of oxygen (yeast)

(fermentation)

2C2H5OH + 6CO2 + 2 ATP

Example the single-celled, non-green plant called ‘yeast’ can live without oxygen because it obtains energy by the process of anaerobic respiration

Anaerobic respiration in humans: We (the human beings) obtain energy by aerobic respiration. But anaerobic respiration can sometimes take place in our muscles (or the muscles of other animals). For example, anaerobic respiration takes place in our muscles during vigorous physical exercise when oxygen gets used up faster in the muscle cells titan can be supplied by the blood. When anaerobic respiration takes place in human muscles (or animal muscles), then glucose (food) is converted into lactic acid with the release of a small amount of energy.

Glucose Glycolysis Pyruvate In the absence of 2lactic + 2 ATP



(1 moloecule)

(in cytoplasm)

(pyruvuic acid)

(2 molecules)

oxygen (muscle tissue)

acid energy

How muscle cramps are caused The anaerobic respiration by muscles brings about partial breakdown of glucose (food) to form lactic

acid. This lactic acid accumulates in the muscles. The accumulation of lactic acid in the muscles causes muscle cramps. Thus, muscle cramps occur due to the accumulation of lactic acid in muscles when the muscles respire an aerobically (without oxygen) while doing hard physical exercise.

How can we get relief from muscle cramp We can get relief from cramps in muscles caused by heavy exercise by taking a hot water bath or a

massage. Hot water bath (or massage) improves the circulation of blood in the muscles. Due to improved blood flow, the supply of oxygen to the muscles increases. This oxygen breaks down lactic acid accumulated in muscles into carbon dioxide and water, and hence gives us relief from cramps.

Similarity between aerobic and anaerobic respiration The similarity between aerobic respiration and anaerobic respiration is that in both the cases, energy

is produced by the breakdown of food like glucose. Differences between Aerobic and Anaerobic Respiration

Aerobic Respiration 1) Aerobic respiration takes place in the presence of

oxygen. 2) Complete breakdown of food occur in aerobic

respiration. 3) The end products in aerobic respiration are carbon

dioxide and water.

4) Aerobic respiration produces a considerable amount of energy.

Anaerobic Respiration

1) Anaerobic respiration takes place in the absence of oxygen.

2) Partial breakdown of food occurs in anaerobic respiration.

3) The end products in anaerobic respiration may be ethanol and carbon dioxide (as in yeast plants) or lactic acid (as in animal muscles)

4) Much less energy is produced in anaerobic respiration.

RESPIRATION IN PLANTS

Oxygen and carbon dioxide are called respiratory gases. Plants get Oxygen by Diffusion. Each part of the plant performs respiration separately.

1. Respiration in Roots

Air is present in-between the particles of soil. The roots of a plant take the oxygen required for respiration from the air present in-between the soil particles by the process of diffusion.

The extensions of the epidermal cells of a root are called root hair. The root hairs are in contact with the air in the soil. Oxygen (from air in the soil particles) diffuses into root hairs and reaches all the other cells of the root for respiration.

Carbon gas produced in the cells of the root during respiration moves out through the same root hairs by process of diffusion.

2. Respiration in Stems

In herbaceous plants:- The stems of herbaceous plants (or herbs) have stomata. So, the exchange of respiratory gases in the

stems of small, herbaceous plants takes place through stomata.



The oxygen from air diffuses into the stem of a herbaceous plant through stomata and reaches all the cells for respiration.

The carbon dioxide gas produced during respiration diffuses out into the air through the same stomata. In hard and woody stems of big plants:- The hard and woody stems of big plants or trees do not have stomata. In woody stems, the bark (outer

covering of stem) has lenticels for gaseous exchange. Lenticels is a small area of bark in a woody stem where the cells are loosely packed allowing the gaseous

exchange to take place between the air and the living cells of the stem. The oxygen from air diffuses into the stem of a woody plant through lenticels and reaches all the inner

cells of the stern for respiration. The carbon dioxide gas produced in the cells of the stern during respiration diffuses out into the air

through the same lenticels. 3. Respiration in Leaves

The leaves of a plant have tiny pores called stomata. The exchange of respiratory gases in the leaves takes place by the process of diffusion through stomata.

Oxygen from air diffuses into a leaf through stomata and reaches all the cells where it is used in respiration. The carbon dioxide produced during respiration diffuses out from the leaf into the air through the same

stomata. Respiration in leaves occurs during the day time as well as at night.

Photosynthesis and respiration during the day time and night time

(i) During day time, when photosynthesis occurs, oxygen is produced. The leaves use some of this oxygen for respiration and the rest of oxygen diffuses out into air. Again, during day time, carbon dioxide produced by respiration is all used up in photosynthesis by leaves. Even more carbon dioxide is taken in from air. Thus, the net gas exchange in leaves during day time is: 02 diffuses out; CO2 diffuses

(ii) At night time, when no photosynthesis occurs and hence no oxygen is produced, oxygen from air diffuses into leaves to carry out respiration. And carbon dioxide produced by respiration diffuses out into air. So, the net gas exchange in leaves at night is: C02 diffuse out; O2 diffuses in.

Difference of respiration in animals and plants

Respiration in plants 1) All the parts of a plant (like root, stem and leaves)

perform respiration individually. 2) During respiration in plants, there is a little

transport of respiratory gases from one part of the plant to the other.

3) The respiration in plants occurs at a slow rate.

Respiration in animals 1) An animal performs respiration as a single unit. 2) Respiratory gases are usually transported over long

distances inside an animal during respiration. 3) The respiration in animals occurs at a much faster

rate.

Diffusion being a slow process is used by plants to get oxygen for respiration. Explain.

Plants have a branching shape, so they have quite a large surface area in comparison to their volume. Therefore, diffusion alone can supply all the cells of the plants with as much oxygen as they need for respiration. Diffusion occurs in the roots, stems and leaves of plant

What happens if land plants remain water logged for considerable time?

The land plants die if they remain waterlogged for a considerable time. This is because too much water expels all the air from in-between the soil particles. Due to this, oxygen is not available to the roots for aerobic respiration. Under these conditions, the roots will respire an aerobically, producing alcohol. This may kill the plant.



RESPIRATIONS IN ANIMALS

Different animals have different modes of respiration

In simple unicellular animals Like Amoeba, respiration takes place by the simple diffusion of gases through the cell membrane.

Most of the animals have, however, specific organs for respiration.

The animals like earthworms which live in the soil use their skin to absorb oxygen from air and move carbon dioxide. So, the respiratory organ in the earthworm is the skin.

The aquatic animals like fish, prawns and mussels have gills as the respiratory organs which extract oxygen dissolved in water and take away carbon dioxide from the body.

In the insects like grasshopper, cockroach, housefly and a mosquito, the tiny holes called spiracles on their body and the air tubes called tracheae are the respiratory organs.

The respiratory organs of the land animals such as man (humans), birds, lizard, dog, and frog, etc., are the lungs. (Frogs, however, breathe both by lungs and skin).

All the respiratory organs (whether skin, gills, trachea or lungs) have three common features. 1) All the respiratory organs have a large surface area to get enough oxygen. 2) All the respiratory organs have thin walls for easy diffusion and exchange of respiratory gases. 3) All the respiratory organs like skin, gills and lungs have a rich blood supply for transporting

respiratory gases (only in the tracheal system of respiration, air reaches the cells directly). Why the breathing rate of aquatic animals is faster than terrestrial animals? The animals which live in water (aquatic animals) use the oxygen dissolved in water to carry out

respiration. Since the amount of dissolved oxygen in water is low as compared to the amount of oxygen in the air, therefore, the rate of breathing in aquatic animals in much faster than in terrestrial animals (or land animals). A faster rate of breathing provides more oxygen to the aquatic animal. The terrestrial animals (or land animals) use the oxygen of air or atmosphere for breathing and respiration.

Why terrestrial animals have an advantage over the aquatic animals? A terrestrial animal has an advantage over an aquatic animal in regard to obtaining oxygen for

respiration that it is surrounded by an oxygen-rich atmosphere from where it can take any amount of oxygen.

Respiration in Amoeba Amoeba is a single-celled animal. Amoeba depends on simple diffusion of gases for breathing. The

diffusion of gases takes place through the thin cell membrane of Amoeba. The exchange of gases in Amoeba takes place through its cell membrane.

Amoeba lives in water. This water has oxygen gas dissolved in it. The oxygen from water diffuses into the body of Amoeba through its cell membrane.

The process of respiration produces carbon dioxide gas continuously. This carbon dioxide gas diffuses out through the membrane of Amoeba into the surrounding water.

How each body part of amoeba gets oxygen?



Since the Amoeba is very small in size, so the oxygen spreads quickly into the whole body of Amoeba This oxygen is used for respiration (energy release) inside the Amoeba cell.

The breathing surface (or respiratory surface) of Amoeba is its cell surface membrane. Examples: Amoeba, Paramecium and Planarian all breathe through their cell membrane. Why unicellular animals do not need blood circulatory system but large multicellular animals need blood

circulatory system?

In the small, single-celled animals such as Amoeba, the volume of their body is so small that oxygen can be introduced quickly into the whole body by the process of diffusion. This is because due to the smallness of Amoeba cell, the oxygen does not have to go far.

In large animals, the volume of body is so big that oxygen cannot diffuse into all the cells of the body quickly. This is because in these cases the oxygen has to travel a very large distance to reach each and every cell of the body. So, in large animals, there is a blood circulatory per system to carry oxygen to all the parts of the body quickly (and remove carbon dioxide).

The blood cells contain respiratory pigments which take up oxygen from air and carry it to the body cell. Human blood contains a respiratory pigment called haemoglobin which carries the oxygen from the lungs to all the body cells very efficiently. Haemoglobin is present in red blood corpuscles.

Why diffusion is insufficient to meet the oxygen requirements in large multi cellular organisms? Diffusion is insufficient to meet the oxygen requirements of large multi cellular organisms like

humans because the volume of human body is so big that oxygen cannot diffuse into all the cells of the human body quickly. This is because oxygen will have to travel large to distances inside the human body to reach each and every cell of the body.

Diffusion being a very slow process will take a lot of time to make oxygen available to all the body cells. For example, it has been estimated that if diffusion were to provide oxygen in our body, then it would take about 3 years for a molecule of oxygen from our lungs to reach our toes by the process of diffusion.

Respiration in Earthworm The earthworm exchanges the gases through its skin. This means that the respiratory surface of an

earthworm is its skin. The skin of an earthworm is quite thin and moist, and has a good blood supply. So, the earthworm

absorbs the oxygen needed for respiration through its moist skin. This oxygen is then transported to all the cells of the earthworm by its blood where it is used in respiration.

The carbon dioxide produced during respiration is carried back by the blood. This carbon dioxide is expelled from the body of the earthworm through its skin. Thus, in earthworm, gaseous exchange takes place through the skin which is thin and moist.

Respiration in Leeches The leeches also absorb the oxygen needed for respiration through their skin. And carbon dioxide

produced inside the leeches (during respiration) also goes out through the skin. Respiration in Fish The fish has special organs of breathing called ‘gills’. The fish has gills on both the sides of its head.

The gills are covered by gill covers so they are not visible from outside. The fish lives in water and this water contains dissolved oxygen in it. For breathing, the fish uses the oxygen which is dissolved in water.



The fish breathes by taking in water through its mouth and sending it over the gills. When water passes over the gills, the gills extract dissolved oxygen from this water. The water then goes out through the gill slits (hidden under the gill cover). Thus, the dissolved oxygen is extracted from water by the fish when it flows over the gills.

The extracted oxygen is absorbed by the blood and carried to all the parts of the fish. The carbon dioxide produced by respiration is brought back by the blood into the gills for expelling into the surrounding water. The fish has no lungs like us, the gaseous exchange in fish takes place in the gills. So, the respiratory surface of a fish is the surface of its gills.

Prawns and mussels also have special organs called ‘gills’ for breathing and respiration. What happens if fish is taken out of water? When a fish is taken out from water it dies Soon (even though there is a lot of oxygen in the air

around it). This is because a fish does not have lungs to use the oxygen of air for breathing and respiration. The fish has gills which can extract only dissolved oxygen from water and provide it to fish. Gills cannot take in the oxygen from air on land. Since fish does not get oxygen for breathing when taken out of water, it dies.

Respiration in Humans. The process by which energy is released from food in our body is called respiration. Carbon dioxide and water are the two by products of respiration. The process of respiration takes

place inside the cells of our body. It involves our respiratory system. The function of respiratory system is to breathe in oxygen for respiration (producing energy from

food), and to breathe out carbon dioxide produced by respiration. The breathing organs of human beings are lungs. It is in the lungs that the gases are exchanged between the blood and air. The gases exchanged between blood and air, are oxygen and carbon dioxide.

Breathing is the process by which air rich in oxygen is taken inside the body of an organism and air rich in carbon dioxide is expelled from the body (with the help of breathing organs.

The taking in of air rich in oxygen into the body during breathing is called ‘inhalation’ and giving out all (or expelling) the air rich in carbon dioxide is called ‘exhalation’. Both, inhalation and exhalation take place regularly during breathing. A breath means ‘one inhalation plus one exhalation’.

When we breathe in air, it is actually the oxygen gas present in air which is utilised by our body in cells (to break down food and produce energy). Thus, we ‘breathe in’ air to supply oxygen to the cells of our body (for the breakdown of food to release energy), and we ‘breathe out’ to remove waste product carbon dioxide from our body (which is produced during the breakdown of food in the cells).

Mechanism of breathing The process of breathing takes place in our lungs. Lungs are connected to our nostrils (holes in the

nose) through nasal passage (or nasal cavity) and windpipe. When we inhale air, it enters our nostrils, passes through nasal passage and windpipe, and reaches our lungs. Our two lungs hang in an airtight space in our body called ‘chest cavity’. Around the sides of the chest cavity is the rib cage with sheets of muscles between the ribs. The rib cage encloses the lungs in it. At the bottom of the chest cavity is a curved sheet of muscle called diaphragm. Diaphragm forms the floor of chest cavity.

Movements of rib cage and diaphragm during breathing



Breathing involves the movements of the rib cage and the diaphragm. This happens as follows: Breathing in:- When we breathe in (or inhale), then two things happen at the same time: (i) the

muscles between the ribs contract causing the rib cage to move upward and outward, and (ii) the diaphragm contracts and moves downward. The upward and outward movement of rib cage, as well as the downward movement of diaphragm, both increase the space in the chest cavity and make it larger. As the chest cavity becomes larger, air is sucked in from outside into the lungs.

Breathing out:- When we breathe out (or exhale), even then two things happen at the same time: (i) the muscles between the ribs relax causing the rib cage to move downward and inward, and (ii) the diaphragm relaxes and moves upward. The downward and inward movement of rib cage, as well as the upward movement of diaphragm, both decrease the space in our chest cavity and make it smaller. As the chest cavity becomes smaller, air is pushed out from the lungs.

RESPIRATORY SYSTEM IN HUMANS (OR MAN) The main organs of human respiratory system

are: Nose, Nasal passage (or Nasal cavity), Trachea, Bronchi, Lungs and Diaphragm.

The human respiratory system begins from the nose. Our nose has two holes in it which are called nostrils. There is a passage in the nose behind the nostrils which is called nasal passage (or nasal cavity).

The nasal passage is separated from the mouth cavity (buccal cavity or oral cavity) by a hard, bony palate.

The nasal passage is lined with fine hair and mucus (Mucus is secreted by the glands inside the nasal passage).

The part of throat between the mouth and wind pipe is called pharynx.

The trachea is a tube which is commonly known as wind pipe. Trachea is supported by rings of soft bones called cartilage.

The upper end of trachea has a voice box called larynx. The trachea runs down the neck and divides into two smaller tubes called ‘bronchi’ at its lower end.

(The singular of bronchi is bronchus). The two bronchi are connected to the two lungs. The lungs lie in the chest cavity or thoracic cavity which is separated from abdominal cavity by a

muscular partition called diaphragm. The lungs are covered by two thin membranes called pleura. The lungs are enclosed in a ‘rib cage’

made of bones called ‘ribs’. Each bronchus divides in the lungs to form a large number of still smaller tubes called ‘bronchioles’.

The smallest bronchioles have tiny air-sacs at their ends. The pouch-like air-sacs at the ends of the smallest bronchioles are called ‘alveoli’ (singular alveolus).

The walls of alveoli are very thin and they are surrounded by very thin blood capillaries. It is in the alveoli that oxygen is taken into the body and carbon dioxide is eliminated.

It is in the alveoli that gaseous exchange takes place. The diaphragm is a sheet of muscle below the lungs. It helps in ‘breathing in’ and ‘breathing out’.

The muscles of chest also help in breathing in and breathing out



Working of respiratory system in humans When we breathe in air, the diaphragm and muscles attached to the ribs contract due to which our

chest cavity expands. This expansion movement of the chest increases the volume inside the chest cavity.

Due to increase in volume, the air pressure decreases inside the chest cavity and air for respiration from outside (being at higher pressure) rushes into our body through the nostrils present in the nose. This air then goes into nasal passage. From the nasal passage, air enters into pharynx and then goes into the wind pipe (or trachea). The air coming from the nostrils during breathing passes through trachea and enters into the lungs.

In this way, during the process of ‘breathing in’ the air sacs or alveoli of the lungs get filled with air containing oxygen. The alveoli are surrounded by very thin blood vessels called capillaries carrying blood in them. So, the oxygen of air diffuses out from the alveoli walls into the blood.

The oxygen is carried by blood to all the parts of the body (This oxygen is carried by a red pigment called hemoglobin present in blood). As the blood passes through the tissues of the body, the oxygen present in it diffuses into the cells (due to its higher concentration in the blood).

This oxygen combines with the digested food (glucose) present in the cells to release energy. Carbon dioxide gas is produced as a waste product during respiration in the cells of the body tissues.

This carbon dioxide diffuses into the blood (due to its higher concentration in body tissues). Blood carries the carbon dioxide back to the lungs where it diffuses into the alveoli.

When we breathe out air, the diaphragm and the muscles attached to the ribs relax due to which our chest cavity contracts and becomes smaller. This contraction movement of the chest pushes out carbon dioxide from the alveoli of the lungs into the trachea, nostrils and then out of the body into the air.

How can we breathe in air even when we are eating food The nasal passage is separated from the mouth cavity (buccal cavity or oral cavity) by a hard, bony

palate so that we can breathe in air even when we are eating food (and the mouth cavity is filled with food).

Explain, how nose ensure the passage of clean air in lungs? The nasal passage is lined with fine hair and mucus (Mucus is secreted by the glands inside the nasal

passage). When air passes through the nasal passage, the dust particles and other impurities present in it are trapped by nasal hair and mucus so that clean air goes into the lungs.

Why Trachea does not collapse even when there is no air in it? Trachea does not collapse even when there is no air in it because it is supported by rings of soft

bones called cartilage. How are the human lungs have been designed to maximize the exchange of gases? The human lungs have been designed to maximize the exchange of gases as follows: There are

millions of alveoli in the lungs. The presence of millions of alveoli in the lungs provides a very large area for the exchange of gases. And the availability of large surface area maximizes the exchange of gases. For example, if all alveoli from the two human lungs are unfolded, they would give an area of about 80 square metres (which is nearly the size of a tennis court!).

Residual volume of air During the breathing cycle, when air is taken in (or inhaled) and let out (or exhaled), the lungs always

contain a certain residual volume of air so that there is sufficient time ‘for the oxygen to be



absorbed’ into the blood and ‘for the carbon dioxide to be released’ from the blood. Carbon dioxide more soluble in water (than oxygen), so it is mostly transported in the dissolved form in our blood.

Exhaled air and inhaled air Less carbon dioxide is present in inhaled air but much more carbon dioxide is present in exhaled air.

Carbon dioxide is produced during respiration (which comes out in exhaled air). The only difference in the inhaled air and exhaled air is that they contain different proportions of oxygen, carbon dioxide and water vapour. (The proportion of nitrogen gas in the inhaled air and exhaled air remains the same, 78 per cent, because it is neither used up in respiration nor produced during respiration.

Inhaled Air Exhaled Air Oxygen : 21% Oxygen : 16.4% carbon dioxide : 0.04% carbon dioxide : 4.4% Water vapour : A little Water vapour : A lot Rate of Breathing The average breathing rate in an adult man at rest is about 15 to 18 times per minute. This breathing

rate increases with increased physical activity. Rapid breathing supplies more oxygen to body cells for producing more energy required for doing physical exercise.

The normal range of haemoglobin in the blood of a healthy adult person is from 12 to 18 grams per decilitre (12 to 18 g/dl) of blood. The deficiency of haemoglobin in the blood of a person reduces the oxygen-carrying capacity of blood resulting in breathing problems, tiredness and lack of energy.

How carbon monoxide is produced? Carbon monoxide gas (CO) is formed whenever a fuel burns in an insufficient supply of air. For example, if coal (or charcoal) is burned in a closed space (like a room with closed doors and

windows), then a lot of carbon monoxide is formed. Why carbon monoxide is poisonous? Haemoglobin has more affinity (or attraction) for carbon monoxide than oxygen. So, if carbon

monoxide gas is inhaled by a person, then this carbon monoxide binds very strongly with haemoglobin in the blood and prevents it from carrying oxygen to the brain and other parts of the body. Due to lack of oxygen, the person cannot breathe properly. If carbon monoxide is inhaled for a long time, then the person becomes unconscious and can even die due to oxygen starvation.

The persons having breathing problems (or respiratory problems) are given oxygen masks to facilitate breathing. In serious cases, the patient is put on a machine called ‘ventilator’ in which a tube is inserted directly into the trachea (or wind pipe) of the patient to help him in breathing comfortably. Before we go further and describe the transport of materials iii plants and animals, please answer the following questions:

TRANSPORT Some arrangement is required inside an organism which can carry the essential substances to all its

parts so that they reach each and every cell of its body. Transport is a life process in which a substance absorbed (or made) in one part of the body of an

organism is carried to other parts of its body. Large organisms (large plants and animals) need transport systems in their bodies to supply all their

cells with food, oxygen, water, and other materials.



Special tissues and organs are needed for the transport of substances in plants and animals because these tissues and organs can pick up the essential substances like food, oxygen, water, etc., at one end of their body and carry them to all other parts.

TRANSPORT IN PLANT Why plants do not need to supplied with te

materials quickly: Plants are less active, so their cells do not need to be supplied with materials so quickly. Also, due to the branching shape of a plant, all the cells of a plant can get oxygen for respiration and carbon dioxide for photosynthesis directly from the air by diffusion.

Function of transport system in plants: The only substances which are to be supplied to a plant through a transport system are water and minerals (which they can’t get from the air. Another job of the transport system of plants is to transport food prepared in the leaves to the various parts of the plant like stems, roots, etc.

Transport systems in plants: The plants have two transport systems. 1. Xylem which carries water and minerals, and 2. Phloem which carries the food materials which the plant makes (Phloem also carries the

hormones made by the plants in their root and shoot tips). The transport of materials in a plant can be divided into two parts.

(i) Transport of water and minerals in the plant, and (ii) Transport of food and other substances (like hormones) in the plant.

Transport of Water and Minerals In the leaves, water is used in making food by photosynthesis. The water and minerals dissolved in it

move from the roots of the plant to its leaves through the two kinds of elements of the xylem tissue called xylem vessels and tracheids. Xylem vessels and tracheids are both non-living conducting tissues which have thick walls.

1. Xylem Vessels Structure: The xylem vessel is a non-living,

long tube which runs like a drainpipe through the plant. A xylem vessel is made of many

hollow, dead cells (called vessel elements), joined end to end.

The end walls of the cells have broken down so a long, open tube is formed. Xylem vessels run from the roots of the plant right up through the stem and reach the leaves.

Xylem vessels do not contain the cytoplasm or nuclei. The walls of xylem vessels are made of cellulose and lignin.



Xylem vessels have pits in their thick cell walls. Define pits: Pits are not open pores. Pits are the thin areas of the cell wall where no lignin has been

deposited. Pits have unthickened cellulose cell wall. Position of xylem: The xylem vessels branch into every leaf of the plant. Function of lignin: Lignin is a very hard and strong substance, so xylem vessels also provide strength

to the stems and help to keep the plant upright. Wood: Wood is made almost entirely of lignified xylem vessels. In what kind of plants xylem vessels or tracheids are present: In flowering plants, either only xylem

vessels transport water or both xylem vessels and tracheids transport water. 2. Trachieds Structure: Tracheids are long, thin, spindle shaped cells with pits in their thick cell walls. Water flows

from one tracheid to another through pits. Tracheids are dead cells with lignified walls but they do not have open ends, so they do not form

vessels. They are elongated cells with tapering ends. Tracheids have pits in their walls, so water can pass from one tracheid to another through these

pits. Although all the plants have tracheids, they are the only water conducting tissue in non-

flowering plants. Structure of roots or cross sectional diagram of roots The outer layer of cells in the root is

called epidermis. Epidermis is only one cell thick. The

layer of cells around the vascular tissues (xylem and phloem) in the root is called endodermis (It is the innermost layer of cortex).

The part of root between the epidermis and endodermis is called root cortex. And the xylem tissue present in roots is called root xylem in a root, the root hair are at its outer edge but the root xylem vessels (which carry water to the other parts of plant) are at the centre of the root.

And in-between the root hair and root xylem are epidermis, root cortex and endodermis. So, before water absorbed by root hair from the soil reaches the root xylem, it has to pass through the epidermis, root cortex and endodermis.

Mechanism of Transport of Water and Mineral in a Plant The roots of a plant have hair called root hairs. The function of root hairs is to absorb water and

minerals from the soil. The root hairs are directly in contact with the film of water in-between the soil particles.

Water (and dissolved minerals) gets into the root hairs by the process of diffusion. The water and minerals absorbed by the root hair from the soil pass from cell to cell by osmosis through the epidermis root cortex, endodermis and reach the root xylem.



The xylem vessels of the root of the plant are connected to the xylem vessels of its stem. So, the water (containing dissolved minerals) enters from the root xylem vessels into stem xylem vessels. The xylem vessels of the stem branch into the leaves of the plants.

The water and minerals carried by the xylem vessels in the stem reach the leaves through the branched xylem vessels which enter from the petiole (stalk of the leaf) into each and every part of the leaf.

Only about 1 to 2 per cent of the water absorbed by the plant is used up by the plant in photosynthesis and other metabolic activities. The rest of water is lost as water vapour into the air through transpiration.

How Water is sucked up by the xylem vessels? The evaporation of water from the leaves of a plant is called transpiration. The leaves of a plant have

tiny pores on their surface which are called stomata. A lot of water from the leaves keeps on evaporating into the air through the stomata. This loss of water (as water vapour) from the leaves of a plant is called transpiration.

Since the cells of the leaf are losing water by transpiration, so water from the xylem vessels in the leaf will travel to the cells by osmosis to make up this loss of water. Thus, water is constantly being taken away from the top of the xylem vessels in the leaves to supply it to the cells in the leaves.

This reduces the effective pressure at the top of the xylem vessels, so that water flows up into them (from the soil). The continuous evaporation of water (or transpiration) from the cells of a leaf creates a kind of suction which pulls up water through the xylem vessels.

In this way, the process of transpiration helps in the upward movement of water (and dissolved minerals) from the roots to the leaves through the stem.

Transport of Food and Other Substances Leaves make food by the process of photosynthesis. The food made by leaves is in the form of

simple sugar (glucose). Other types of substances called plant hormones are made in the tips of roots and shoots.

The transport of food from the leaves to other parts of the plant is called translocation. Thus, phloem translocates the food (or sugar) made in the leaves. The movement of food materials (and other substances like hormones) through phloem depends on the action of living cells called sieve tubes.

Phloem Contains Sieve Tubes Phloem is made of many cells joined end to end

to form long tubes the end walls of the cells which form phloem are not completely broken down.

The end walls of cells in the phloem form sieve plates, which have small holes in them. These holes in the sieve plates allow the food to pass along the phloem tubes. The cells of phloem are called sieve tubes (or sieve elements).

Sieve tubes which form phloem are living cells which contain cytoplasm but no nucleus. The sieve tube cells do not have lignin in their walls. Each sieve tube cell has a companion cell next to it. The companion cell has a nucleus and many other organelles. Companion cells supply the sieve tubes with some of their requirements.



Why translocation is necessary: The translocation (transport of food from leaves to other parts of the plant) is necessary because every part of the plant needs food for obtaining energy, for building its parts and maintaining its life.

The movement of water (and dissolved salts) in xylem is always upwards (from soil to leaves) and it is caused by the suction of water at the top because of low pressure created by transpiration from leaves. The movement of food in phloem can be, however, upwards or downwards depending on the needs of the plant.

Mechanism of Transport of Food in a Plant The movement of food in phloem (or translocation) takes place by utilising energy. This happens as follows: The food is made in the mesophyll cells (or photosynthetic cells of a leaf. The food (like sugar) made

by the mesophyll cells of a leaf enters into the sieve tubes of the phloem. Interconnected phloem tubes are present in all the parts of the plant.

The sugar (food) made in leaves is loaded into the sieve tubes of phloem tissue by using energy from ATP.

Water now enters into sieve tubes containing sugar by the process of osmosis due to which the pressure in the phloem tissue rises. This high pressure produced in the phloem tissue moves the food to all the parts of the plant having less pressure in their tissues. This allows the phloem to transport food according to the needs of the plant.

For example, in spring, even the sugar stored in the root or stem tissue of a plant would be transported through phloem to the buds which need energy to grow.

BLOOD Blood is a red coloured liquid which circulates in our body. Blood is red because it contains a red

pigment called haemoglobin in its red cells. Blood is a connective tissue. The main components of blood are

1. Plasma, 2. Red Blood Corpuscles (or Red Blood Cells), 3. White Blood Corpuscles (or White Blood Cells), and 4. Platelets

Blood is a liquid (or fluid matrix) called plasma with red cells, white cells and platelets floating in it. Plasma The liquid part (or fluid part) of blood is called plasma. Plasma is a colourless liquid which consists normally of water with many substances dissolved in it.

Plasma contains about 90 per cent water. Plasma also contains dissolved substances such as proteins, digested food, common salt, waste products (like carbon a dioxide and urea), and hormones.

Plasma carries all these dissolved substances from one part to another part in the body. Red blood cells Structure: Red blood cells are circular in shape. Red blood cells do not have nuclei. Life: Red blood cells have to be made quickly because they do not live for very long. Each red blood

cell lives for about four months. Colour: Red blood cells are red in colour due to the presence of a red pigment called haemoglobin

inside them.



Function: Red blood cells (RBC) are carriers of oxygen. Red blood cells carry oxygen from the lungs to all the cells of the body. It is actually the haemoglobin present in red blood cells which carries oxygen in the body.

Importance or function of haemoglobin: Haemoglobin performs a very important function of carrying oxygen from lungs to body tissues. Haemoglobin also carries some of the carbon dioxide from body tissues to the lungs (most of carbon dioxide is carried by plasma of blood in the dissolved form).

Why the life of RBCs is short? One reason for the short life of red blood cells is that they do not have nuclei. When we donate blood we do not feel weakness. Why? It has been estimated that about three million red blood cells of the human blood die every day but

four times that number are made in the bone marrow everyday. So, when we donate blood to save the life of a person, then the loss of blood from our body can be made up very quickly, within a day. This is because red blood cells are made very fast in our bone marrow.

White Blood Cells Structure: White blood cells are either spherical in shape or irregular in shape. All the white blood

cells have a nucleus though the shape of nucleus is different in different types of white blood cells. White blood cells (WBC) in the blood are much smaller in number than red blood cells.

Function: White blood cells fight infection and protect us from diseases. This is because white blood cells help to fight against germs and other foreign bodies which cause diseases. Some white blood cells can eat up the germs (like bacteria) which cause diseases. Other white blood cells make chemicals known as ‘antibodies’ to fight against infection. In other words, white blood cells manufacture antibodies which are responsible for providing immunity in our body (due to which we are protected from disease and infection).

Other name of WBC and why they are called so: White blood cells are called soldiers of the body. This is because they protect the body from the attack of disease-causing germs (pathogens) and other harmful foreign materials.

Platelets Platelets are the tiny fragments of special cells formed in the bone marrow. Platelets do not have nuclei. Platelets help in the coagulation of blood (or clotting of blood) in a cut

or wound. When a cut or wound starts bleeding, then platelets help clot the blood (make the blood semi-solid) due to which further bleeding stops.

Where blood cells are made: All the blood cells are made in the bone marrow from the cells called

stem cells. Function of Blood The important functions of blood in our body are as follows: 1. Blood carries oxygen from the lungs to different parts of the body. 2. Blood carries carbon dioxide from the body cells to the lungs for breathing out. 3. Blood carries digested food from the small intestine to all the parts of the body. 4. Blood carries hormones from the endocrine glands to different organs of the body (where they are

needed). 5. Blood carries a waste product called urea from the liver to the kidneys for excretion in urine.



6. Blood protects the body from diseases. This is because white blood cells kill the bacteria and other germs which cause diseases.

7. Blood regulates the body temperature. This is because the blood capillaries in our skin help to keep our body temperature constant at about 37°C.

Transport in Humans The main transport system in human

beings (or man) is the ‘blood circulatory system’.

In the human circulatory system, blood carries oxygen, digested food and other chemicals like hormones and enzymes to all the parts of the body.

It also takes away the waste products (or excretory products) like carbon dioxide and urea produced in the body cells.

The human blood circulatory system consists of the heart (the organ which pumps and receives the blood) and the blood vessels (or tubes) through which the blood flows in the body. The blood flows through three types of blood vessels (i) arteries, (ii) veins, and (iii) capillaries.

In addition to the blood circulatory system for the transport in human beings, there is another system called lymphatic system which also helps in the transport of materials in the human body.

HUMAN CIRCULATORY SYSTEM The various organs of the circulatory system in humans are: Heart, Arteries, Veins and Capillaries.

Blood is also considered a part of the circulatory system. So, the human circulatory system consists of the heart, arteries, veins, capillaries, and blood. The heart acts as a pump to push out blood. The arteries, veins and capillaries act as pipes (or tubes) through which the blood flows. These tubes which carry blood are called blood vessels.

Structure of heart The heart is roughly triangular in shape. It is made of special muscle called cardiac muscle. The size

of our heart is about the same as our ‘clenched fist’. The heart has four compartments called ‘chambers’ inside it. The upper two chambers of heart are

called atria (singular atrium), and the lower two chambers of heart are called ventricles. The two atria receive blood from the two main veins. And the two ventricles transport blood to the

entire body and the lungs. The left atrium is connected to the left ventricle through a valve V1. Similarly, the right atrium is

connected to the right ventricle through another valve V2.



These valves prevent the backflow of blood into atria when the ventricles contract to pump blood out of the heart to the rest of the body. This is because when the ventricles contract, the valves V1 and V2, close automatically so that the blood may not go back into atria.

The job of heart is to pump blood around our body. All the atria and ventricles of the heart contract and relax (expand) at appropriate times and make the heart behave like a pump. Since ventricles have to pump blood into various organs with high pressure, they have thicker walls than atria.

A sheath of tissue called ‘pericardium’ protects the muscular heart. The chambers of the heart are separated by a partition called septum.

The arteries, veins and capillaries are a kind of thin pipes (or tubes) through which blood flows in vessels which carry blood from the heart to all the parts of the body.

Structure and function of arteries

Structure: Arteries are the thick walled blood vessels which carry blood from the heart to all the parts of the body.

Why arteries are thick walled: Arteries have thick walls because blood emerges from the heart under high pressure.

Position of arteries: Arteries are found in the whole of our body. The main artery (called aorta) is connected to the left ventricle of the heart through a valve V3.

Function of arteries: The main artery carries oxygenated blood from the left ventricle to all the parts of the body (except the lungs). Another artery called pulmonary artery is connected to the right ventricle of the heart through another valve V4. The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs.

Structure and function of blood capillaries

Structure: The capillaries are thin walled and extremely narrow tubes or blood vessels which connect arteries to veins.

Position: Thus, the capillaries are in- between the arteries and veins. The blood from arteries enters the capillaries in the body. Every living cell of our body is close to a capillary. The other end of capillaries is joined to some wider tubes called veins. The deoxygenated blood (or dirty blood) coming from the capillaries enters into veins.

Why the walls of capillaries are thin: the walls of capillaries are only one- cell thick so the various dissolved substances (like oxygen, food, etc.) present in blood pass into the body cell through the thin walls of the capillaries. At the same time, the waste substances (like carbon dioxide) formed in the cells enter into capillaries.

Function: The exchange of various materials like oxygen, food, carbon dioxide, etc. between the blood and the body cells takes place through capillaries.

Structure and function of vein

Structure: Veins are the thin walled blood vessels which carry blood from all the parts of the body back to the heart. Veins have valves in them.

Why veins have thin walls: Veins do not have thick walls because the blood flowing through them is no longer under high pressure.

Why veins have valves: Veins have valves in them which allow the blood in them to flow in only one direction (towards the heart). The valves prevent the backflow of blood in veins.



Position: Veins are also found in the whole of our body. Function: The pulmonary vein is connected to the left atrium of the heart. The pulmonary vein carries

oxygenated blood from lungs back to the heart. There is also a main vein (called vena cava). The main vein is connected to the right atrium of the heart. The main vein carries deoxygenated blood from all the parts of the body (except lungs), back to the heart. Difference between the artery and vein

The main difference between an artery and a vein is that an artery carries blood from the heart to the body organs whereas a vein carries blood from the body organs back to the heart.

Heart as double pump: Heart is really a double pump. The left side of heart (left atrium and left ventricle) act as one pump which pumps blood into the whole body, except the lungs. The right side of heart (right atrium and right ventricle) acts as another pump which pumps blood only into the lungs. The two pumps in the heart work

independently. The separation of left

and right sides of the heart is necessary

to prevent the mixing of the

oxygenated blood on the left side with

the deoxygenated blood on the right

side.

Define oxygenated blood: The blood carrying oxygen in it is called oxygenated blood.

Where do we get oxygenated blood: We get oxygenated blood in the lungs where the fresh oxygen of air passes into the blood.

Define deoxygenated blood: The blood having no oxygen in it is called deoxygenated blood. Where do we get deoxygenated blood: The deoxygenated blood is formed in all the organs of the body

(except the lungs). This is because when the oxygenated blood passes through the organs of the body, the body cells use up its oxygen and make it deoxygenated. The deoxygenated blood, however, carries carbon dioxide in it (which is produced during respiration in body cells.

Why does heart beats all the time: The heart beats non- stop all the time. The heart beat is due to the rhythmic contraction and relaxation of the heart muscles which make up the atria and the ventricles.

Contraction and expansion of atria and ventricle: The two atria (left atrium and right atrium) contract together and relax together. Similarly, the two ventricles (left ventricle and right ventricle) contract together and relax together. The contraction of two atria is immediately by the contraction of the two ventricles. The heart beats (or beating of heart) circulates the blood in the human body.

The circulation of blood in the human body.

1. When the muscles of all the four chambers of the heart are relaxed, the pulmonary vein brings the oxygenated blood (oxygen- carrying blood) from the lungs into the left atrium of the heart.

2. When the left atrium contracts, the oxygenated blood is pushed into the left ventricle through the value V1.



3. When the left ventricle contracts, the oxygenated blood is forced into the main artery called ‘aorta’. This main artery then branches into smaller arteries which go into different body organs (except the lungs). The smaller arteries (called arterioles) further branch into capillaries

4. The main artery carries blood to all the organs (or parts) of the body like head, chest, arms, stomach, intestine, liver, Kidney, trunk and legs (except the lungs). When the oxygenated blood passes through the capillaries of the body organs, then it gives oxygen to the body cells. Since the blood loses its oxygen here, we say that the blood has been deoxygenated. The blood also gives the digested food and other dissolved materials to the body cells. At the same time, carbon dioxide produced as a waste material during respiration enters into the blood. The deoxygenated blood (carrying carbon dioxide) from the body organs enters into the main vein called vena cava. The main vein carries the deoxygenated blood to the right atrium of the heart.

5. When the right atrium contracts, deoxygenated blood is pushed into the ventricle through the valve V2. 6. And when the right ventricle contract, the deoxygenated blood is pumped into the lungs through the

pulmonary artery. In the lungs, deoxygenated blood releases its carbon dioxide and absorbs fresh oxygen from air. So, the blood becomes oxygenated again. This oxygenated blood is again sent to the left atrium of heart by pulmonary vein for circulation in the body.

Double circulation

A circulatory system in which the blood travels twice through the heart in one complete cycle of the body is called double circulation.

In the human circulatory system the pathway of blood from the heart to the lungs and back to the heart is called pulmonary circulation; and the pathway of blood from the heart to the rest of the body and back to the heart is called the systemic circulation. These two types of circulation taken together make double circulation.

Heart of mammals and birds

The animals such as mammals (including human beings), and birds four – chambered heart (which consists of two atria and two ventricles).

In a four- chambered heart, the left side and right side of the heart are completely separated to prevent the oxygenated blood from mixing with deoxygenated blood.

Such a separation allows a highly efficient supply of oxygen to the body cells which is necessary for producing a lot of energy. This energy is useful in warm- blooded animals (like mammals and birds) which have high energy needs because they constantly require energy to maintain their body temperature.

All the animals having four- chambered hearts have double circulation in which the blood passes through the heart ‘twice’ in one complete cycle of the body.

Heart of amphibians and reptiles

The animals such as amphibians and many reptiles are cold – blooded animals whose body temperature depends on the temperature in the environment.

They do not need energy to maintain their body temperature and hence their requirement of energy is less. The amphibians (like frogs) and reptiles (like lizards) have a three- chambered heart (which consists of two

atria and one ventricle). Due to incomplete division within their heart, the oxygenated and deoxygenated bloods mix to some extent in amphibians and reptiles have, however, a double circulation that delivers blood to the lungs and the rest of the body, respectively.

Heart of fish

The fish has a two-chambered heart (which consists of one atrium and one ventricle). The fish does not have lungs, it has gills to oxygenate blood.



In a fish, the heart pumps deoxygenated blood to the gills. Oxygenation of blood takes place in the gills. The oxygenated blood from the gills is supplied to the body parts of the fish where oxygen us utilized and carbon dioxide enters into it making it deoxygenated. This deoxygenated blood returns to the heart to be pumped into gills again.

The flow of blood in a fish is called single circulation because the blood passes through the heart of fish only once in one complete cycle of the body.

Heart Beats

One complete contraction and relaxation of the heart is called a heart beat. The heart usually beats about 70 to 72 times in a minute when we are resting. This means that the heart pumps out blood to the arteries about 70 to 72 times per minute.

Number of heart beats increases too much after a physical exercise or when a person is excited. For example, if we count our heart beats after running for a while, we will find it to be more than 100 per minute.

The heart beats faster during and after an exercise because the body needs more energy under these conditions. The faster beating of heart pumps blood more rapidly to the body organs which supplies more oxygen to the body cells for rapid respiration to produce more energy.

Pulse

Define: The expansion of an artery each time the blood is forced into it, is called pulse. Each heartbeat generates one pulse in the arteries, so the pulse rate of a person is equal to the number of

heart beats per minute. Since the heart beats about 70 to 72 times per minute. Thus, the pulse rate is the same as the heart rate.

Just like heartbeats, the pulse rate of a person is higher after a physical exercise or when a person is excited. How can we measure pulse: The pulse is traditionally taken above the wrist.

The pulse can be felt with fingers placed gently on arteries at the wrist. We place the first two fingers (index

finger and middle finger) of our right hand on the inner side of our left wrist and press it gently. We will feel

some waves touching our fingers. These waves are the pulse. We can count the number of such waves (or

thumpings) in one minute by using a watch. This will give us the pulse rate (per minute).

Blood Pressure

The pressure at which blood is pumped around the body by the heart is called blood pressure. The blood pressure of a person is always expressed in the form of two values called ‘systolic pressure’ and ‘diastolic pressure’.

The maximum pressure at which the blood leaves the heart through the main artery (aorta) during contraction phase, is called the systolic pressure.

This high pressure in the main artery maintains a steady flow of blood in all the arteries towards the capillaries.

The minimum pressure in the arteries during the relaxation phase of heart is called the diastolic pressure. The value of diastolic pressure is always lower than that of the systolic pressure. The blood pressure of a person is expressed in terms of millimeters of mercury (which is written as mm Hg). The normal blood pressure values are:

Systolic pressure: 120 mm Hg Diastolic pressure: 80 mm Hg

This is usually written as 120/80

A young person may have blood pressure of 110/75 but at the age of 60 years it could be 145/90.



High blood pressure is called hypertension. High blood pressure is caused by the constriction (narrowing) of very small arteries (called arterioles) which results in increased resistance to blood flow. Very high blood pressure can lead to rupture of an artery and internal bleeding.

How do Food and Oxygen Reach Body Cells

The liquid from the blood which is forced out through the capillary walls and moves between all the body cells (providing them with food and oxygen, and removing carbon dioxide) is called tissue fluid.

The walls of blood capillaries are very thin. So, when blood flows through the capillaries, a liquid called tissue fluid leaks from the blood capillaries and goes into tiny spaces between the various body cells in the tissues.

The tissue fluid carries food and oxygen from the blood to the cells, and picks up their waste products like carbon dioxide. After doing its job, most of the tissue fluid seeps back into blood capillaries.

This remaining tissue fluid carrying large protein molecules, digested fat, germs from the cells and fragments of dead cells, enters into another type of tiny called lymph capillaries and it becomes lymph. This lymph (along with its contents) is returned to the blood by another type of transport system in the human body called lymphatic system.

LYMPHATIC SYSTEM

A system of tiny tubes called lymph vessels (or lymphatics) and lymph nodes (or lymph glands) the human body which transports the liquid called lymph from the body tissues to the blood circulatory system is called lymphatic system.

The lymphatic system consists of the following parts: 1. Lymph capillaries 2. Larger lymph vessels, 3. Lymph nodes (or lymph glands), and 4. Lymph.

Structure of lymphatic system

Lymphatic system contains lymph capillaries. Lymph capillaries are tiny tubes which are present in the whole body (just like blood capillaries).

The lymph capillaries join to form larger lymph vessels. The lymph vessels have lymph nodes (or lymph glands) at interval.

The lymph vessels are connected to large veins of the blood circulatory system.

What special cells do lymph nodes contain and what is the function of those cells: The lymph nodes contain special type of cells called lymphocytes. Lymph nodes containing lymphocytes are involved in the cleaning of lymph and protecting the body from disease.

How lymph capillaries are different form blood capillaries: Lymph capillaries are differ from blood capillaries in two ways: Lymph capillaries are closed ended (the end of

lymph capillaries in the tissues of the body is closed, and the pores in the walls of lymph capillaries are bigger in size (than that of blood



capillaries). The ends of the lymph of capillaries in the body tissues are closed, so the tissue fluid can only seep into the walls of the lymph capillaries present in the body tissue.

The pores in the walls of the lymph capillaries are somewhat bigger, so even large protein molecules present in the tissue fluid can enter into lymph capillaries (which could not pass into blood capillaries).

What is lymph: Lymph is a light yellow liquid which is somewhat similar in composition to blood plasma. Why lymph is not red like blood: Lymph is not red like blood because it does not contain red blood cells. Composition of lymph: Lymph contains large protein molecules and digested food (which come into from the

tissue fluid between the cells). It also contains germs from the cells are fragments of dead cells. Lymph contains a special type of white blood cells called lymphocytes which help in fighting infection and disease.

Flow of lymph: Lymph is another medium of circulation in the human body. But lymph flows in only one direction- from body tissues to the heart.

Why lymph is called extracellular fluid: Lymph is derived from the tissue fluid which remains outside the cells of the body, so it is also called extracellular fluid.

Working of lymphatic system

Lymph containing large protein molecules, digested fat, germs and fragments of dead cells from the tissue fluid around the body cells seeps into the lymph capillaries present throughout the body.

From lymph capillaries, lymph passes into larger lymph vessels containing lymph nodes. In the lymph nodes, lymph is cleaned by white blood cells called lymphocytes. These white blood cells eat the

germs and dead cells, and also make antibodies for protecting the body from disease. The cleaned lymph containing large protein molecules, digested fat and other materials is transported by

lymph vessels to the large veins (called subclavian veins) which run just beneath the collar bone. These veins carry the lymph to the heart.

In this way, the circulation of lymph from the body tissues to the heart is completed.

The functions of lymph (or Lymphatic System)

Lymph (or lymphatic system) takes part in the nutritive process of the body. For example, it put into circulation large protein molecules by carrying them form the tissues into the blood stream (which could not be absorbed by blood capillaries due to their large size). Lymph also carries digested fat for the nutritive process.

Lymph (or lymphatic system) protects the body by killing the germs drained out of the body tissues with the help of lymphocytes contained in the lymph nodes, and by making antibodies.

Lymph (or lymphatic system) helps in removing the waste products like fragments of dead cells, etc.

EXCERTION

The process of removal of toxic wastes from the body of an organism is called excretion.

EXCRETION IN PLANTS

Waste products of plants: Gaseous wastes: The main waste products produced by plants are carbon dioxide, water vapour and

oxygen. Carbon dioxide and water vapour are produced as wastes during respiration by plants whereas oxygen is produced as a waste during photosynthesis.

Solid wastes: The plants also store some of the waste products in their body parts. For example, some of the waste products collect in the leaves, bark and fruits of the plant (or trees).

Plants also produce some liquid wastes also in the form of gums and resins. Removal of gaseous wastes:



The gaseous wastes of respiration and photosynthesis in plants (carbon dioxide, water vapour and oxygen) are removed through the ‘stomata’ in leaves and ‘lenticels’ in stems and released to the air.

The plants excrete carbon dioxide produced as a waste during respiration only at night time. This is because the carbon dioxide produced during respiration in day time is all used up by the plant itself in photosynthesis.

The plants excrete oxygen as a waste only during the day (because oxygen is produced by photosynthesis only during the day time when the sunlight is there).

Water vapour produced as a waste by respiration is, however, excreted by plants all the time (day as well as night). This waste water is got rid of by transpiration.

Removal of solid wastes: The plants get rid of these solid wastes by shedding of leaves, peeling of bark and felling of fruits. So,

when the dead leaves, bark and ripe fruits fall off from a tree, then the waste products contained in them are got rid of.

Some of the plant waste stored in the fruits of the plant in the form of solid bodies called raphides. These wastes are removed when the fruits get detached from the plant. For example, the fruit called ‘yam’ (Zamikand) has needle – shaped raphides on its surface.

Removal of liquid waste: The plants secrete their wastes in the form of gum and resins from their stems and branches. The plant also excretes some waste substances into the soil around them.

How do plants get rid of their waste products

The plant get rid of gaseous waste products through stomata in leaves and lenticels in stems. The plants get rid of stored solid and liquid wastes by the shedding of leaves, peeling of bark and felling of

fruits. The plants get rid of wastes by secreting them in the form of gums and resins. Plants also excrete some waste substances into the soil around them.

EXCRETION IN ANIMALS

Amoeba: In Amoeba (and other single celled animals), the waste material carbon dioxide is removed by diffusion through the cell membrane, but nitrogenous wastes (like ammonia) and excess water are removed by the contractile vacuole.

Earthworm: In earthworm, the tubular structures called nephridia are the excretory organs. In addition to nephridia, the moist skin of earthworm also acts as an excretory organ.

Human beings: In human beings, the microscopic thin tubes from nephron, which function as excretory unit. About 1 million nephrons taken together from the excretory organ of human beings called Kidney.

Removal of Waste Products in Humans

Waste products: The major wastes produced by the human body are: carbon dioxide and urea. Carbon dioxide is produced as a waste by the oxidation of food during the process of respiration. Urea is produced as a waste by the decomposition of unused proteins in the liver.

Why waste material should be removed: Our body must get rid of these waste materials because their accumulation in the body is poisonous and harms us. Waste removal is called excretion.

Excretory organs: The human body has different organs for the removal of wastes from the body. These are our lungs and kidneys. Our lungs excrete carbon dioxide. Our kidneys excrete urea. The kidneys are the main excretory organs of the human body. So, the main excretory system in human beings involves the kidneys.

Removal of gaseous waste products: Carbon dioxide is produced as a waste product in the body by the oxidation of food during respiration. This carbon dioxide enters from the body tissues into the blood stream by diffusion. Blood carries this carbon dioxide to the lungs. When we breathe out, then the lungs excrete carbon dioxide which goes into the air through nostrils. Thus, our lungs act as the excretory organs for removing the waste product carbon dioxide from the body.



Structure of excretory system in humans

The excretory system of human beings consists of the following main organs: Two kidneys, Two ureters, Bladder and Urethra.

The kidneys are bean shaped organs towards the back of our body just above the waist. Every person has two kidneys.

The blood in our body is constantly passing through our kidneys. The renal artery (or kidney artery) brings in the dirty blood (Containing waste substances) into the kidneys.

The function of kidneys is to remove the poisonous substance urea, other waste salts and excess water from the blood and excrete them in the form of a yellowish liquid called urine.

Thus, kidneys clean our blood by filtering it to remove unwanted substances present in it. The cleaned blood is carried away from the kidneys by the renal vein (or kidney vein).

The ureters (or excretory tubes), one from each kidney, opens into urinary bladder.

Urine is stored in the bladder. The bladder is a bag which stores urine till the time we go to the toilet. The urethra is a tube.

The urine collected in the bladder is passed out from the body through the urethra.

Structure of nephrons

Each kidney is made up of a large number of excretory units called nephrons. The nephron has a cup- shaped bag at its upper end which is called Bowman’s capsule. The lower end of

Bowman’s capsule is tube –shaped and it is called a tubule. The Bowman’s capsule and the tubule taken together make a nephron.

One end of the tubule is connected to the Bowman’s capsule and its other end is connected to a urine-collecting duct of the kidney.

The Bowman’s capsule contains a bundle of blood capillaries which is called glomerulus (plural glomeruli). One end of the glomerulus is attached to the renal artery which brings the dirty blood containing the urea waste into it. The other end of glomerulus comes out of Bowman;s capsule as a blood capillary, surrounds the tubule of nephron and finally joins a renal vein (passing



urea-free clean blood into it).

Function of nephrons or kidney

The function of glomreulus is to filter the blood passing through it. Only the small molecules of substances present in blood like glucose, amino acids, salts, urea and water etc., pass through the glomerulus and collect as filterate in the Bowman’s capsule.

The large molecules like proteins and blood cells cannot pass through the glomerulus capillaries and hence

remain behind in the blood. The function of tubule of nephron is to allow the selective reabsorption of the useful substances like glucose, amino acids, salts and water into the blood capillaries (which surround it). But the waste material like urea remains behind in the tubule. It does not get reabsorbed into blood capillaries.

The dirty blood containing waste like urea (brought by renal artery) enters the glomerulus. The glomerulus filters this blood. During filtration, the substances like glucose, amino acids, salts, water and urea, etc present in the blood pass into Bowman’s capsule and then enter the tubule of nephron.

When the filtrate containing useful substances as well as the waste substances passes through the tubule, then the useful substances like all glucose, all amino acids, most salts and most water, etc. are reabsorbed into the blood through blood capillaries surrounding the tubule.

Only the waste substances urea, some unwanted salts and excess water remain behind in the tubule. The liquid left behind in the tubule of nephron is urine.

The nephron carries this urine into the collecting duct of the kidney from where it is carried to under. From the urine passes into urinary bladder. Urine is stored in the bladder for some time and ultimately passed

out of the body through urethra. Please note that the human urine contains water, some salts and nitrogenous substances, most of which is

urea (and some uric acid).

Renal Failure (Kidney Failure) and the Technology for Survival

Sometimes, a person’s kidneys mat stop working. An infection in the kidneys, an injury to kidneys, very high blood pressure, very high blood sugar or restricted blood flow to the kidneys, can damage the kidneys due to which they stop working.

Complete failure of the kidneys allows the urea and other waste products to build up in the blood. Even the amount of water in the body is not regulated. This will cause death if the patient is not given immediate treatment.



The best long term solution for kidney failure is the kidney transplant. The damaged kidney is removed and a latching kidney donated by a healthy person is transplanted in its place by a surgical operation.

If a kidney transplant is not possible due to some reasons, then the patient with Kidney failure is treated periodically on a kidney machine (by a procedure called dialysis). This is because a kidney machine can do the work of damaged kidneys.

The kidney machine sometimes called ‘artificial kidney’. An artificial kidney is a device to remove nitrogenous waste products from the blood through dialysis.

Dialysis

The blood of a person having kidney failure can be cleaned regularly by using a kidney machine dialysis machine). The procedure used for cleaning the blood of a person by separating the waste substance (urea) from it is called dialysis.

The blood from an artery in the patient’s arm is made to flow into the dialyser of a dialysis machine made of long tubes of selectively permeable membrane (like cellulose) which are coiled in a tank containing dialyzing solution.

The dialyzing solution contains water, glucose and salts in similar concentrations to those in normal blood. As the patient’s passes blood through the dialyzing solution, most of the wastes like urea present in it pass

through the selectively permeable cellulose tubes into the dialyzing solution. The clean blood is pumped back into a vein of the patient’s arm.



Assignment

NUTRITION




Choose correct answer from the given option:

(i) Which of the following provides energy for photosynthesis?

(a) Chloroplast (b) sunlight (c) water (d) carbon dioxide

(ii) The correct sequence of the organs of digestive system is

(a) Pharynx → oral cavity → oesopgagus → stomach → small intestine → large intestine

(b) oral cavity→ Pharynx → oesopgagus → stomach → small intestine → large intestine

(c) Pharynx → oral cavity → oesopgagus → stomach → small intestine → large intestine

(d) oral cavity→ Pharynx → stomach → oesopgagus → large intestine → small intestine

(iii) the vermiform appendix is situated below the caecum and communicates with

(a) colon (b) small intestine (c) large intestine (d) rectum

(iv) islets of langerhans are situated in

(a) pancreas (b) liver (c) gall bladder (d) spleen

(v) bile is secreted by

(a) gall bladder (b) liver (c) gastric gland (d) spleen

(vi) carbohydrates, proteins and fats are completely digested in the

(a) large intestine (b) stomach (c) small intestine (d) colon

(vii) villi are found in the inner walls of

(a) small intestine (b) large intestine (c) oesophagus (d) stomach

(viii) gastric gland are located in the wall of the

(a) small intestine (b) large intestine (c) stomach (d) oesophagus

(ix) The main function of finger-like villi is to

(a) Crush the food for digestion

(b) Allow the food to get mixed properly with enzymes

(c) Secrete enzymes which speed up digestion

(d) Increase the absorptive area of the intestine

(x) The carnivorous animals (meat eaters) have shorter intestine because

(a) They swallow the food (c)) meat is easier to digest

(b) Meat is partly digest in the mouth (d) none of the above

(xi) The breakdown of pyruvate to give carbon dioxide, water and energy takes place in

(a) Cytoplasm (b) mitochondria (c) chloroplast (d) nucleus

(xii) The autorophic mode of nutrition requires

(a) Carbon dioxide and water (c) sunlight

(b) Chlorophyll (d) all of the above

2. What are life process?

3. Do organism require some kind of energy for the performance of life process? If yes, what is the source of

that energy?

4. Why is diffusion insufficient to meet the oxygen requirements of multi-cellular organisms like humans?



5. What criteria do we use to decide whether something is alive?

6. Summarise the process of photosynthesis with the help of a chemical equation showing the reactant and

products.

7. Define the following terms:

(i) Autotrophs (ii) saprotrophic nutrition (ii) parasitic nutrition (iv) holozoic nutrition

8. What are the end products of photosynthesis?

9. What is the role of stomata in the process of photosynthesis?

10. What is the mode of nutrition for amoeba?

11. State whether the following statements are True or False:

(i) All teeth in humans have similar structure.

(ii) All humans have same type of digestive system.

(iii) Bile juice has no digestive enzymes.

(iv) Digestion of carbohydrates takes place in the stomach of human beings.

(v) All kinds of plants are autotrophs.

(vi) Saprotrophic nutrition is found in Agaricus, Mucor, Fungi.

(vii) In Amoeba, digestion is extracellular.

(viii) The products of photosynthesis are carbon dioxide, water and starch.

12. Give a word equivalent for the following:

(i) Breaking of complex organic molecules into simpler food molecules.

(ii) Organisms which prepare their own food.

(iii) Animals which depend for their food directly or indirectly on plant.

(iv) The association of two organisms in which both are benefitted with the association.

(v) The process by which organisms prepare their own food with the help of solar energy, raw

materials (CO2, water) and release O2.

(vi) Animals which feed on plants and animals.

(vii) The small openings located on the lower and upper surface.

13. Why are plants considered as producers?

14. What is the sources of energy used by plants in photosynthesis?

15. In which part of the alimentary canal are villi present?

16. In which part of the alimentary canal is digested food absorbed?

17. Name the source of salivary amylase.

18. Name one animal each with extracellular and intracellular digestive system.

19. Which plant material is not acted upon by any enzymes in the human alimentary canal?

20. Name two autotropic bacteria.

II. Short answer questions (2 marks)


1. Mention the role of bile in the digestion of food.

2. Why is energy needed even during sleep?

3. Mention any two ways in which digested food is utilized by the body.

4. What is the role of acid in our stomach?

5. What is the function of digestive enzymes?

6. Why does acid not erode the wall of the intestine?

7. Where does protein digestion take place in the human alimentary canal? Also name the protein digestion

enzyme.

8. Differentiate between the following:

(i) Ingestion and digestion. (v) large intestine and small intestine



(ii) Digestion and assimilation (vi) carnivore and herbivore

(iii) Intracellular and extracellular digestion (vii) autotroph and heterotroph

(iv) Saprophytic and parasitic nutrition

9. What are outside raw materials used for by an organism?

10. What process would you consider essential for maintaining life?

11. What are the differences between autotrophic nutrition and heterotrophic nutrition?

12. Where do plant get each of the raw materials required for photosynthesis?

13. What is the role of saliva in the digestion of food?

14. Name one enzyme present in pancreatic juice and give its functions.

15. What is the role of liver in the process of digestion of food?

16. What are gastric juices? Where are they secreted?

17. Give differences between autotrophic and heterotrophic nutrition.

18. In human alimentary canal, name the part:

(i) Where food is completely digested

(ii) Which secrete juice that has typsin enzyme

(iii) That secretes bile juice

(iv) That absorbs water from unabsorbed food

19. A gas is released during photosynthesis. Name the gas and also state the way in which this gas is evolved.

20. In certain group of plants, stomata remains close during day. How is food synthesized by such plants. Also

name them.

21. How does use of KOH prove that CO2 is essential for photosynthesis?

22. How does diffusion help in performing several life processes in single-celled organisms?

23. What are parasitic plants? Cite one example of such a plant.

24. How is used energy stored in plants?

25. State one example of an organism that

(i) Breakdown the food material outside the body and then absorb it.

(ii) Derive nutrition from plants or animals without killing them.

26. What peristalsis?



1. What would happen if green plants disappear from the earth?

2. Why is nutrition essential for living beings?

3. Why biologists consider viruses as living?

4. Mention the functions of each kind of teeth present in human mouth.

5. Explain with the help of diagram how amoeba takes its nutrition.

6. Explain how is a leaf well adapted to play an effective role in the process of photosynthesis.

7. Observe the diagram given below:

(i) Identify

(ii) Label the (a) stomata, (b) air space, (c) chloroplasts (d) upper epidermis in the diagram.



8. (i) Label the parts of the two diagrams given below.

(ii) What do they represent?

(iii) Do they have any role to play life process of plants? Give the role.

9. Plants are immobile and they remain fixed. How will you decide that they are living?

10. How is the small intestine designed to absorb digested food?

11. How are fats digested in our bodies? Where does this process take place?

12. What are the necessary conditions for a autotrophic nutrition and what are its by-products?

13. What are the differences between aerobic and anaerobic respiration? Name some organisms that use the

aerobic mode of respiration.

14. In human alimentary canal, name the site of complete digestion of various components of food. Explain

the process of digestion.

15. Name three different glands associated with the digestive system in humans. Also their secretions.

16. Explain how does paramecium obtain its food.

17. (i) A product is formed in our muscles due to breakdown of glucose when there is a alck of oxygen. Name

the product and also mention the effect of build up of this product.

(ii) Differentiate between fermentation in yeast and aerobic respiration on the basis of end products

formed.

18. Mention the names of any two secretions released by the gastric glands and state one role played by each

in our body.

19. Mention the role of following in digestion:

(i) Pepsin (ii) saliva (iii) villi

20. List the role of each of the following in our digestive system:

(i) Muscles of stomach wall (ii) hydrchloric acid (iii) mucus

21. Give reason why:

(i) Herbivores have longer small intestine as compared to carnivores.



(ii) Mucus is secreted with hydrochloric acid in the stomach.

22. Plants have low energy needs as compared to animals. Give reason.

23. (i) Transport of food in plants requires living tissues and energy. Justify this statement.

(ii) Name the components of food that are transported by the living tissues.

24. Describe the process of starch digestions, specifying site, glands and enzymes used and end-products

produced.

25. Write one feature which is common to each of the following pairs?

(i) Glycogen and starch (ii) chlorophyll and haemoglobin (iii) Gills and lungs

26. Name the end-products formed due to digestion of:

(i) Proteins (ii) carbohydrates (iii) fats

27. With the help of schematic flowchart show the breakdown of glucose in a cell to provide energy.

(i) In the presence of oxygen (ii) in the absence of oxygen (iii) when there is lack oxygen



1. What would happen if green plants stop preparing their food? Explain.

2. Differentiate between intracellular and extracellular digestion. Explain with the help of examples.

3. Name the digestive enzymes released in stomach and intestine. Mention the nutrients they digest.

Mention the medium in which they act.

4. How does food move down in the alimentary canal? Describe.

5. (i) Draw a diagram to show open stomatal pore and label on it: (a) guard cells (b) chloroplast.

(ii) State two functions of stomata.

(iii) How do guard cells regulate the opening and closing of stomatal pore.

6. (i) Draw the cross-section of a leaf and label the following parts: (a) upper epidermis (b) chloroplast (c)

cuti.

(ii) Define photosynthesis. List three events which occur during photosynthesis. Write chemical equation

involved during photosynthesis.

7. (i) Draw a diagram of human alimentary canal and label on it: (a) stomach (b) liver (c) pancreas (d) small

intestine.

(ii) Explain the role of bile juice in digestion food.

8. Draw a diagram of human alimentary canal and label: (i) organ which transports food from mouth to

stomach (ii) organ which secretes bile juice (iii) organ which stores bile (iv) organ in which absorption of

digested food takes place.

RESPIRATION



1. Multiple choice questions

i. The percentage of oxygen in inspired air is

(a|) 21% (b) 17% (c) 14% (d) 79%

ii. The percentage of carbon dioxide in inspired air is

(a) 0.3% (b) 0.03% (c) 4% (d) 6%

iii. The respiration in whale takes place by

(a) gills (b) lungs (c) skin (d) both a and b

iv. Which of the following respire anaerobically?

(a) yeast (b) grasshopper (c) amoeba (d) fish



v. Which cell organelle is called the ‘ power hose’ of the cell?

(a) lysosome (b) golgi bodies (c) ribosome (d) mitochondria

vi. Instant source of energy is given by the oxidation of

(a) fat (b) amino acid (c) glucose (d) protein

vii. Kreb’s cycle takes place in

(a) golgi bodies (b) mitochondria (c) lysosome (d) cytoplasm

2. Name the process that helps in the breakdown of food taken by organism to produce energy.

3. Define: (i) Respiration (ii) Aerobic respiration (iii) Anaerobic respiration

4. Name the organs of respiration in a fish and human beings.

5. With the help of a simple chemical equation represent the process of respiration.

6. Write the full form of the abbreviations ATP and ADP.

7. Name the part of the body where the actual exchange of gases (CO2 and O2) takes place human beings.

8. Name the intermediate compound formed in the process of respiration.

9. What are the organs of respiration in most of the terrestrial animals?

10. What are alveoli? Where are they found?

11. Name the respiratory pigment which helps in respiration in our body.



1. Why fishes die when taken out of water?

2. How do plants respire? Name the structure through which exchange of gases takes place.

3. Define anaerobic respiration. Name the chemical substance formed in the body as a result of anaerobic

respiration.

4. Why do plants not give out carbon dioxide during the day, as a result of respiration?

5. What is the role of hair and mucous that lime the passage of nostrils during the exchange of gases?

6. What is trachea? Where is it found in the human respiratory organs?

7. Under what circumstances anaerobic respiration is carried out by human beings?

8. What is the role of stomata in the process of respiration in plants?

9. How are the alveoli designed to maximize the exchange of gases?

10. What would be the consequences of a deficiency of haemoglobin in our bodies?

11. Why do the walls of trachea not collapse when there is less air in it?

12. Why do we feel cramps in our muscles during sudden physical activity?

13. What is inhalation and exhalation?

14. How does exchange of gases take place at the tissue level?



1. Distinguish between the following:

(i) Breathing and respiration (ii) external respiration and internal respiration (iii) alveolar air and

inspired air

2. Why is breathing through nose said to be healthier than taking in air through the mouth?

3. List significant of respiratory surface.

4. Why is it not advisable to breathe in a closed room in winters where an ‘Angithi’ is burning?

5. What role does haemoglobin play in the process of respiration?

6. List three characteristics of lungs which make it an efficient respiratory surface.

7. The diagram given alongside is an important part of human respiratory system. Identify it and describe its

function.

8. Give reason:



(i) Rings of cartilage are present in trachea.

(ii) Lungs always contain a residual volume of air.

9. Why is the rate of breathing in aquatic organisms much faster than in terrestrial organisms.

10. List three differences between aerobic respiration and anaerobic respiration.

11. Explain how is the process of ‘breathing in’ brought about in our body.

12. How are alveoli designed in human beings to maximize the exchange of gases? List three features.

13. Why is aerobic respiration more efficient than anaerobic respiration?



1. What are the different ways in which glucose is oxidized to produce energy in various organisms?

2. How are oxygen and carbon dioxide transported in human beings?

3. How are the lungs designed in human beings to maximize the area for exchange of gases?

4. Describe double circulation in human beings. Why is it necessary.

5. Draw a diagram of human respiratory system and label the following:

(i) part where air is filtered by fine hair and mucus

(ii) part which terminates in balloon-like structures

(iii) balloon-like structures where exchange of gases takes place

(iv) part which separates chest activity from abdominal cavity.

TRANSPORTATION IN HUMAN BEINGS




i. The transportation of water from the root hair to the top of the plant is done with the help of

(a) phloem (b) xylem (c) cambium (d) both a and b

ii. Which one of the following is the smallest blood vessel?

(a) Artery (b) Vein (c) Capillary (d) Vena cava

iii. The food material is translocated in the plants through

(a) xylem (b) phloem (c) epidermis (d) parenchyma

iv. Which of the following contains deoxygenated blood?

(a) Pulmonary vein (b) pulmonary artery (c) carotid artery (d) aorta

2. Define: (i) Blood (ii) Lymph (iii) Heart

3. In which form (medium)-liquid (dissolved) or solid form, does the transport of materials take place in

living organisms?

4. Name the medium which transport food, carbon dioxide, nitrogenous wastes, salt and other substances

in the human body.

5. What makes blood move in different parts of the body all the time to carry out the function of

transportation?

6. What is the role of haemoglobin in the blood?

7. How many chambers are there in the human heart?

8. Name the chamber of human heart.

9. How does water rise in tall trees?

10. How do root hair help in transportation?



1. What are blood vessels? Name two main kinds of blood vessels.

2. How is oxygen transported by blood from lungs of the tissues?



3. What are platelets? Where are they found?

4. What is lymph? Give its two functions.

5. Leaves of a healthy potted plant were coated with Vaseline to block the stomata. Will this plant remain

healthy for long? State three reasons for your answer.

6. State how is heart protected. Name the tissue which constitutes the heart. What is the advantage of

having four-chambered heart?

7. How is food transported in plants?

8. Why is it necessary to separate oxygenated and deoxygenated blood in mammals and birds?

9. How does transpiration help in absorption of water from roots?

10. What are the differences between the transport of materials in xylem and phloem?

11. Why are arteries have thick elastic walls?

12. Why do veins have valves?

13. Blood goes only once through the heart in fish. Give reasons.

14. What is the usefulness of root pressure?

15. Which chamber are ‘receiving chambers’ and which chambers send blood from the heart?

16. What are the different strategies used by plants for transportation of water and minerals during day and

night?

17. Why is transportation of water slow in plants as compared to animals?

18. What would be the consequences of deficiency of haemoglobin in our bodies?


(answer the questions in about 50 words)

1. Mention four important characteristics of the human heart.

2. How is the oxygenated blood prevented from mixing with the deoxygenated blood?

3. Name the four chambers of the heart. Mention what kind of blood each carries.

4. What is the role of lungs in the circulatory system?

5. How many chambers are found in hearts of fishes, amphibians, reptiles and birds?

6. State the differences between blood and lymph.

7. Where do you find platelets? What is their role?

8. The transport and exchange of oxygen and carbon dioxide is shown below with the help of a schematic

representation. The figure however does not label the following pulmonary vein from lungs, pulmonary

artery to lungs, vena cava from body, Aorta to body, right and left auricles and ventricles. Label them.

9. The figure given alongside has been drawn to explain an important phenomenon of plants.

(i) Name the phenomenon.

(ii) Explain its importance.



(iii) What does the direction of arrows indicate?

10. What is the significance of transpiration?

11. How are water and minerals transported in plants?

12. List the three kinds of blood vessels of human circulatory system and write their functions.

13. List three differences between arteries and veins.

14. Explain how lymph returns to the heart.



1. Describe the structure of the heart with the help of simple outline diagram of heart.

2. What are the components of transport system in human beings? What are the functions of these

components?

3. What is the clotting of blood? Make a flow chart showing major events.

4. What are the components of transport system in highly organised plants?

5. Draw the diagram of sectional view of human heart and on it name and label the following parts:

(i) The chamber of the heart that pumps out deoxygenated blood.

(ii) The blood vessel that carries away oxygenated blood from the heart.

(iii) The blood vessel that receives deoxygenated blood from the lower part of our body.

(iv) Structure/part that divides heart into right and left halves and prevents mixing of oxygenated

and deoxygenated blood.

6. (i) Draw a sectional view of the human heart and label on it: (a) pulmonary artery (b) right auricle (c) vene

cava (d) pulmonary vein.

(ii) explain why ventricles have thick muscular walls as compared to artria.

7. What is double circulation? Why is it found in birds and mammals and not in fishes? How is oxygen and

carbon dioxide transported in blood?

8. What is lymph? How is the composition of lymph different from blood plasma? What is the direction of its

flow? List two functions of lymphatic systems.

EXCRETORY SYSYTEM

I. VERY SHORT ANSWER QUESTIONS (1 MARKS)



Choose the correct answer from the given options:

(i) Carbon dioxide is excreted out of the body through the

(a) Kidneys (b) lungs (c) skin (d) liver

(ii) Ammonia gets converted into urea in the



(a) Kidneys (b) liver (c) pancreas (d) gall bladder

(iii) The glomerulus receive blood in the tubule through the

(a) Efferent arteriole (c) renal artery

(b) Afferent arteriole (d) renal vein

(iv) The urine is stored temporarily in the

(a) Ureter (b) urinary bladder (c) kidney (d) urethra

(v) The structural functional unit of kidney is

(a) Glomerulus (b) bowman’s capsule (c) nephron (d) neuron

(vi) The passage of urine from the kidneys to the urinary bladder is through the

(a) Urethra (b) urinary bladder (c) kidney tubules (d) ureter

(vii) Which of the following waste is most toxic for the body?

(a) Urea (b) ammonia (c) uric acid (d) carbon dioxide

(viii) The amount of urine excreted by a normal human being under normal conditions in 24 hours is

(a) 1500 to 2000 mL (b) 2000 to 2500 mL (c) 1000 to 2000 mL (d) more than 2500 mL

(ix) The kidney in human beings is a part of the system for

(a) Nutrition (b) respiration (c) excretion (d) transportation

2. What is the main function of excretory system in our body?

3. What are the main organs of excretion?

4. How are the excretory products formed in different parts of the body brought to the kidneys?

5. Do all animals have an excretory system?

6. Name the excretory products in human beings.

7. Name the filtration units of kidneys.

8. Mention the role of the following:

(i) Ureter (ii) urethra (c) nephron (d) urinary bladder



1. How does excretion in plants take place?

2. How is the amount of urine produced regulated?

3. Define excretion. Name any two substances that are selectively reabsorbed.

4. Name the functional units of kidney. How do they function?

5. What will happen to a person if his kidneys are damaged?

6. Name the important parts of human excretory system.

7. What are the methods used by plants to get rid of their excretory products?

8. Name the factors on which the amount of water reabsorbed along the tubular part of nephron depend

on.

9. State the role of renal artery and kidney.

10. What happens to glucose that enters the nephron along with filtrate?



1. Why do living organisms require an excretory system?

2. What may happen if the excretory products are allowed to accumulate in the body?

3. The diagram given here is part of the structural and functional unit of kidney. Observe the diagram

carefully.

(i) Identify the part (ii) label the parts shown by arrows.



4. What is the role of skin, lungs and intestine in the process of excretion in humans?

5. Mention the purpose of making urine.

6. Define transpiration. State its two functions.

7. List two major steps involved in the formation of urine and state in brief their functions.

8. Why is dialysis done to a patient suffering from kidney failure?



1. Explain the human excretory system.

2. The figure given below shows the excretory system in human beings.

Label the: kidney, ureter, urinary bladder and urethra.

3. The figure given below shows a uriniferous tubule or nephron. Label only the blood vessels which bring

and take away the blood from the unit.



4. Describe the structure and functioning of nephrons.

5. (i) State two advantages of transpiration to the plant body.

(ii) List in tubular form two ways in which ‘transpiration’ is different form ‘translocation’.

Why do plants have a slow transport system.

Animals : Nervous system :-

It comprises neurons, nerves, nervous organs which control the activities of different organs of

the body.

Neuron is the structural and functional unit of nervous system. It is the largest cell of the body

also.

Neuron (or nerve cell) has three components.

(i) Cell Body (or Cyton)

(ii) Axon and

(iii) Dendrites

Control and Cordination



Cell body is a rounded, stellate part of neuron that contains a central nucleus, abundant

cytoplasm and various cell organclles except centrioles. It maintains the neuron through its

metabolic activity and growth.

Axon has an insulating and protective sheeth (or cover) of myelin around it. Myelin is made up of

fat and protein.

Dendrites are fine, short and branched protoplasmic processes of cell body that pick up

sensations (physical, mechanical, electrical, chemical) and transmit the same to the cell body.

The neurons transmit the messages to the nervous system in the form of electrical signals. They

pass the impulse to the cell body and then along the axon. The axon passes th impulse to

another neuron through a function called synapse.

There are three types of neurons :

(i) Sensory neuron : it transmits impulses from sensory cells(or receptor) towards the central

nervous system.

(ii) Motor Neuron : It transmits impulses from the central nervous system towards the

muscle cells (or effectors).

(iii) Relay neuron : it occurs in the central nervous system where they serves as links between

other neurons.

A microscopic gap between a pair of adjacent neurons over which nerve impulses pass when

going from one neuron to the next is called a synapse.

Reflex Action : It is an involuntary and automatic response to a stimulus. It is rapid, automatic,

definite response to stimulus by an organ without involving brain for its initiation. The pathway

which is followed by this is called reflex arc.

Stimulus receptor Organ Sensory Neuron Spinal Cord Motor Neurons Effector Organ

Reflex arcs continue to be more efficient for quick responses.

There are two types of reflexes :

(i) Simple or unconditional reflexes – These reflexes are regulated through spinal cord (CNS) and

participation of brain is not necessary.

(ii) Conditional Reflexes : In these reflexes, the participation of brain is essential .

Nervous system of man consists of three parts –

(i) Central Nervous System, which includes brain and spinal cord.

(ii) Peripheral Nervous System, comprises of nerves arising from brain and spinal cord.

(iii) Autonomic Nervous System.

Olfactory lobes are concerned with sense of smell.



Brain is inside the cavity called cranium, weighs about 1325 gm. It is covered by thin, non-

nervous layer (piameter). It is filled with cerebrospinal fluid. It is divided into three parts –

(a) Forebrain :- (i) Olfactory lobes (ii) Cerebrum



(b) Midbrain

(c) Hind brain :- (i) Cerebellum (ii) Medulla oblongata (iii) Pons

Fore brain (Cerebrum) is the main thinking part of the brain. It is site of our faculties such as

learning, reasoning, intelligence, personality and memory. All our thoughts, sensations, actions

and movements are controlled by the cerebrum.

Midbrain consist of nerve cells, connects forebrain to the hind brain. It has reflex centres for eye

movement and hearing response.

Hind brain (Cerebellum) is the second largest part of brain. Cerebellum maintains posture,

regulates muscle tone.

Medulla oblongata controls involuntary movements, acts as reflex centre for vomiting, coughing,

sneezing, swallowing etc.

Pons – it takes part in regulating respiration.

CO – ORDINATION IN PLANTS :-

The plants coordinate their behaviour against environmental changes by using hormones.

The plants respond to various stimuli very slowly by growing.

Plants show two types of movements :

(i) Movement dependent on growth

(ii) Movement independent on growth.

The plant movements made in response to external stimuli fall two main categories :

(i) Tropism and

(ii) Nastic

TROPISM (TROPIC Movements) :

A growth movement of a plant part in response to an external stimulus in which the direction of

stimulus determine the direction of response is called tropism.

Types of Tropism :

(i) Phototropism – movement in response to light.

(ii) Geotropism – movement in response to gravity.

(iii) Chemotropism – movement in response to chemical.

(iv) Hydrotropism – movement in response to water.

(v) Thigmotropism – movement in response to touch.

Nastic (Nastic movements) : The main difference between tropic and nastic movements is that

tropic movement is a directional movement of a plant part but nastic movement is not a

directional of the plant part with respect to the stimulus.

Thigmonasty : It is the non – directional movement of a plant part in response to the touch of an

object. E.g. Mimosa pudica (Chui – mui)

Photonasty :

Auxins : It stimulates growth, phototropism, geotropism 2, 4 – D is used to avoid pre – harvest

fruit in oranges, apples, used as weedicides. Auxins prevent potato sprouting.

Gibberellins : These can increase the height of plant, can induce parthenocarpy, stimulate

flowering.



Cytokinins : promote cell division, inhibit or delay ageing, organ formation.

Ethylene : It’s a gaseous plant hormone, used in artificial ripening of fruits, promote ageing in

plants, breaks dormancy of several organs.

Abscisic Acid (A.B.A) : Also known as stress hormone. It is a growth inhibitor, inhibit the process

of flowering, seed development.

HORMONES IN ANIMALS .......

Hormones are the substances which help in control and coordination of the body activities.

Exocrine glands are mammary glands, salivary gland, sweat gland.

Endocrine glands are pituitary, thyroid, adrenal.

Pancreas, testes and Ovary are endocrine as well as exocrine gland.

S.No. Endocrine Gland Location Hormones Functions

1. Hypothalamus Brain Releasing Hormones

Regulates the secretion of hormones from pituitary gland.

2. Pituitary (Master Gland)

At the base of Brain

Growth Hormone

Regulates tissue and bone growth.

Trophic Hormones

Regulates the secretion of hormones from endocrine gland like adrenal, thyroid, testes and ovary.

Prolactin Stimulates milk production from mammary glands.

Vasopressin (ADH antidiuretic hormone)

Controls the amount of water reabsorbed by kidney (Osmoregulation)

Oxytocin Regulates of milk from mammary glands.

3. Thyroid Just below neck Thyroxine Regulates metabolism of carbohydrate, fat and proteins and growth rate.

Too much of hormone lead to thinness and over activity.

Too little of it causes over weight and sluggishness.

Deficiency causes Goitre.

4. Para Thyroid Near the Thyroid Parathormone gland

Calcium and Phosphorous metabolism or Calcitonin.

5. Thymus On the chest close to heart

Thymosin Production of antibodies and immune response.

6. Adrenal Just above kidneys

Adrenalin & Cortisone

Helps in regulation of blood pressure, heart rate, carbohydrate metabolism and mineral balance.

7. Pancreas In the abdomen Insulin Regulates sugar metabolism,



near stomach too little insulin leads to high sugar level in blood, causing diabetes.

Glucagon Increases blood glucose

8. Testes Outside the lower abdomen in scrotum

Testosterone . Sperm production. . regulation of male accessory sex organs and secondary sexual characters like beard, and voice.

9. Ovary In the lower abdomen

Estrogen and Progesterone

. Egg production.

. Development of sexual characters like mammary glands, hair pattern voice, maintenance of pregnancy.

sa 1... science .. class 10

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