chapter 5 , 6, 7

THE COMPOSITION OF AIR

Air is everywhere around usAir cannot be seen because it is colourless.However, we can feel the movement of air or wind around usWe can also feel air moving in and out of our nose when we breatheLiving things need air in order to liveAir is one of the most important resources that sustain life

NITROGEN

Nitrogen is an inactive gas

Nitrogen is colourless, has no smell and no taste, does not support combustion.

OXYGEN

Oxygen is necessary for respiration, burning, rusting and decay

Oxygen is set free during the process of photosynthesis

INERT GASES

Inert gases in air are helium, neon, argon, krypton, xenon and radon

Inert gases are very inactive

CARBON DIOXIDE

Carbon dioxide is released during respiration, burning and decay

Carbon dioxide is absorbed by green plants during photosynthesis

Contents Percentage (%)Nitrogen 78Oxygen 21

Carbon dioxide 0.03Inert gases 0.9

Water vapour, dust, microorganisms

variable

Content of air and its percentage

Properties of oxygen and carbon dioxideACTIVITY OXYGEN CARBON

DIOXIDE•Water level in test tube goes up a little•Slightly soluble in water

•Water level in test tube goes up slightly higher•More soluble in water than oxygen

•Nothing happens•Not soluble in sodium hydroxide solution

•Level of solution in test tube is high•Very soluble in sodium hydroxide solution


DIOXIDE•Light up the glowing split•Support combustion

•Puts out the glowing splinter•Does not support combustion

•The lighted split burns more brightly•Supports combustion

•Puts out burning splinter•Does not support combustion


DIOXIDE•Nothing happens•No effect on litmus paper•A neutral gas

•Blue litmus paper; Change to red•Red litmus paper; no change of colour•An acidic gas

•No change •Lime water turns chalky


DIOXIDE•Nothing happens•No effect on bicarbonate indicator

•Change the colour of bicarbonate indicator from red to yellow

Oxygen and carbon dioxide are both colourless and

ouderless gases

TEST FOR OXYGEN

Glowing wood splint that bursts into flame shows the existence of oxygen

TEST FOR CARBON DIOXIDE

Comparison of the Properties of Oxygen and Carbon Dioxide

Summary of the Properties of Oxygen and Carbon Dioxide

OXYGEN IS NEEDED IN RESPIRATIONRespiration begins with every breath you takeProducts of respiration are energy, carbon dioxide and water vapourDuring respiration, living things use oxygen and give out carbon dioxide

The energy produced is use by the cells to carry out living processes

1. After some time, the marker moves towardsi) the germinating seeds in test tube Wii) the grasshopper in test tube X

Living things use oxygen during respiration

2. The marker in test tube does not move at all3. This shows that the germinating seeds and

grasshopper use up oxygen in the test tube and giveout carbon dioxide which is absorbed by the sodium hydroxide solution

4. This causes a decrease in the volume of air inside the test tube, causing the marker to move inwards

5. Test tube Y is a control

Inhaled and Exhaled Air in Humans

In the process of breathing, air from the surrounding is inhaled or sucked into the lungs. This air is known as inhaled air

Inhaled air

Air that is exhaled or breathed out from the lungs is known as exhaled air

Exhaled air

A comparison of inhaled and exhaled air is shown bellow

OXYGEN IS NEEDED FOR COMBUSTION

1. Combustion (i) commonly known as “burning”(ii) A chemical reaction of a substance with oxygen(iii) Give out heat and light(iv) Take place when oxygen, fuel and heat are

present

1. Air pollution occurs when the atmosphere contains pollutants

2. Air pollutants are harmful chemicals or substance present in the air

3. They can affect human beings and the environment in a negative way

4. Examples of air pollutants are smoke, carbon monoxide, oxides of nitrogen, sulphur dioxide, lead and chlorofluorocarbon

THE SOURCES AND EFFECTS OF AIR POLLUTANTS

Life without clean air

BLURRED VISION

e.g. dust or smoke in the air

blurs vision

HEALTH PROBLEMSe.g. lead causes blood

poisoning and brain damage

DEFORMITIESe.g. radioactive

waste causes deformities

in urborn babies

THE GREENHOUSE EFFECTe.g. man will live

in a warmer environment

A REDUCTION IN AGRICULTURAL PRODUCTION

e.g. sticks to leaves and slows down the process of photosynthesis

ACID RAINe.g. metal objects

corrode and the pH of soil and water

sources is lowered

EXAMPLES OF WAYS TO KEEP THE AIR CLEAN

1. Use unleaded fuels2. Use public transport when available. 3. Avoid open burning. Burn plastic waste in

incinerators4. Plant trees in your surroundings5. Reduce, reuse and recycle used items whenever

possible. Buy and use recycled products6. Buy and use products in their non-aerosol form.

Propellants used in aerosol cans contribute to pollution

FORMS OF ENERGY1. Energy is the ability to do work

2. The unit of energy is the joule (J)

3. There are various forms of energy:-- potential energy- kinetic energy- heat energy- light energy- chemical energy- sound energy- electric energy- nuclear energy

POTENTIAL ENERGY1. Potential energy is the energy stored in an object due to

its elevated position, or its condition when the object is:-a) lifted upb) compressedc) stretchedd) bent

2. Examples of objects that contain potential energy:-

The water at the topof a waterfall

A boy walking up a staircasegains potential energy

A bent plastic ruler

A stretched cord of a bow

A compressed spring

A wound spring of a toy car

A stretched rubber band

KINETIC ENERGY

1. Kinetic energy is present in any object that is moving

2. Kinetic energy enables things to move

3. Examples of things that have kinetic energy are

A spinning fan A flying bird A moving car A moving hammer

A flying aeroplane A falling coconut

A swinging pendulum A spinning top A boy running

HEAT ENERGY

1. Heat energy is the energy found in hot objects2. Heat energy is released when we burn fuels such as

charcoal, firewood, petrol and natural gas3. The sun is our main source of heat energy4. Heat energy can be detected by our skin5. Examples of heat energy are given below

Burning wood Hot water Hot iron Gas stove and heated pot

LIGHT ENERGY

1. Objects that produce light are said to have light energy2. The sun is our main source of light energy3. Light energy can be detected by our eyes4. Green plants use light energy from the sun to carry out

photosynthesis

lighted candle lighted lamp lightning sun

SOUND ENERGY

1. All sounds and noises are forms of energy2. Without sound energy, the world would be silent3. Sound energy is produced when objects vibrate4. Sound energy is energy we can hear5. Examples of objects that produce sound energy are:-

television phone ringing radio

ELECTRICAL ENERGY

1. Electrical energy is the energy that makes electrical appliance such as computer, televisions, fans, washing machines and radios work

2. Electrical energy is a very useful form of energy as many things cannot function without it

television radio computer fan

NUCLEAR ENERGY

1. Nuclear energy is the energy stored in the nucleus of an atom

2. One way in which nuclear energy is released is when one big atom is split into many smaller atoms

3. Examples of objects that contain or release nuclear energy are:-a) atomic bombb) nuclear reactor in electricity-generating power station

4. Nuclear energy is used to generate electrical energy

CHEMICAL ENERGY1. Chemical energy is the energy stored in chemical

substances2. Substances which contain chemical energy include

a) chemical substances such as hydrochloric acid and batteriesb) foods such as glucose, bread and ricec) fuel such as coal, charcoal, petrol and diesel

VARIOUS SORCES OF ENERGY

ENERGY CHANGESENERGY CHANGES

1. Energy cannot be created or destroyed.2. Energy can change from one form to another3. We use an energy converter to change energy from one

form into another4. The energy converter changes one form of energy into

another form that is needed to do a certain work5. Examples:-

1. GREEN PLANTS1. Green plants are natural energy converters2. The change light energy from the sun into

chemical energy 3. The chemical energy is stored in various part of

the plants such as leaves, stems, roots and fruits

Light energy chemical energy

2. FAN1. A fan changes electrical energy into kinetic

energy

Electrical energy kinetic energy

3. TELEVISION

1. A television changes electrical energy into light energy and sound energy

Electrical energy Light + Sound energy

4. RADIO1. A radio changes electrical energy into sound

energy

Electrical energy sound energy

5. IRON1. An iron changes electrical energy into heat

energy

Electrical energy heat energy

SOURCES OF ENERGY

FOSSIL FUELS•Coal•Petroleum •Natural gas

WATER (HYDROELECTRIC

ENERGY)

GEOTERMALENERGY

WIND ENERGY

BIOMASS ENERGY

ENERGY FROMRADIOACTIVESUBSTANCCES

WAVE ENERGY

SOLAR ENERGY

THE SUN AS THE PRIMARY SOURCE OF ENERGY

1. The primary source of energy is the sun

2. Most of the energy sources on the Earth originate from the sun indirectly

Light

Heat

Plant

Animals

Photosynthesis

Chemical energyEaten byDie and decay

Electrical energySolar cells

causes

Rain / River

Heat energy

Electrical energyHydro electric

power station

Solar panelscausesWind

Wave

causesHeat energy

Wave energy

The Sun as Our Source of Energy

RENEWABLE AND NON-RENEWABLE ENERGY

1. The sources of energy in the world can be classified into two groupsa) Renewable energy sourcesb) Non-renewable energy sources

2. Renewable energy sources can be replenished or renewed when they have been used

3. Non-renewable energy sources cannot be replenished or renewed and will eventually be used up and exhausted

4. The chart below shows the classification of energy sources

Sources of energy

Renewable energy sources Non-Renewable energy sources

• Sun• Wind• Waves• Tides• Water• Biomass• Geothermal

• Fossil fuels (coal, petroleum, natural gas)

• Radioactive substances(Nuclear energy)

Advantage and disadvantage of different energy sources

ENERGY ENERGY SOURCESSOURCES

ADVANTAGEADVANTAGE DISADVANTAGEDISADVANTAGE

Hydroelectric energy

•The electricity produced is cheap and does not pollute the environment

•Dams and power stations are expensive to build•Only suitable in mountainous areas with good rainfall

Wind energy •Does not pollute the environment

•Wind turbines stop working if there is no wind



Wave energy •Does not pollute the environment

•Only generates electricity twice a day during high and ebb tides

Biomass energy

•Reduces environment burdens

•Releases gases such as carbon dioxide and sulphur dioxide which pollute the environment

Solar energy •Can be produced continuously•Does not pollute the environment

•Cannot work at night or only operates during the day while the sun is shining



Firewood •Can be used in areas that lack energy supply for cooking

•Releases smoke which pollutes the environment

Geothermal energy

•Does not pollute the environment

•Only available where hot water is located close to the earth’s surface

Fossil fuel •High energy value

•Produces gases which are poisonous and forms acid rain such as sulphur dioxide



Radioactive substance

•Very high energy value

•Gives off harmful radiation which can cause cancer•Very expensive to build power stations

Sources of energy

Pollute the environment Do not pollute the environment

• Fossil fuels (coal, petroleum, natural gas)

• Radioactive substances (nuclear energy)

• Biomass• Firewood

• Hydroelectric energy• Wind energy• Wave energy• Solar energy• Geothermal energy

Sources of energy that pollute and do not pollute the environment are shown in the chart on the following page

THE IMPORTANCE OF CONSERVING ENERGY SOURCES

Why do we need to conserve energy?

1. Fossil fuels are the most widely used fuels in the world

2. Motor vehicles and electrical power generators run on fossil fuels

3. As fossil fuels are non-renewable, it is very important for us to conserve energy so that Earth’s reserve of fossil fuels will be able to sustain our needs for a longer period of time

How can we help to conserve energy?

1. We can help to conserve energy by

•Using less energy

•Reducing energy wastage

•Using energy efficiently

Use Energy Efficiently

Use energy- saving bulbs

Car – pool with your

friends

Use energy- saving electrical appliances

Do not place your refrigerator near the stove

Clean your vacuum cleaner filter after use

Iron your clothes all at one time

2. Some of the ways we can use energy efficiently are

The importance of conserving energy sources

1. We should use and manage energy sources carefully by practising good habits such as

•Using public transport•Car-pooling•Switching off electrical appliances when not using them•Ensuring water taps tightly shut so that no water drips from them•Recycling materials•Reusing materials•Reducing the use of materials

HEAT AS A FORM OF ENERGY

The Sun gives out heat

1. Heat is a form of energy2. The sun is the primary source of heat energy3. We feel hot when we stand under the sun because it

gives out heat

Other Sources of Heat

1. Heat is also produced by:- rubbing or friction- burning- collision- electricity

HEAT

1. Heat is a form of energy2. When heat energy is supplied to a substance, the

temperature of the substance will rise

Uses of Heat

1. Heat is very useful to us2. Heat is used for:

- drying- cooking- ironing- keeping warm- boiling

TEMPERATURE

1. Temperature is the measure of the degree of hotness of a substance

2. Temperature is not a measure of the quantity of heat in a substance

3. Temperature is defined as the degree of hotness or coldness

4. The unit for temperature is degrees Celsius (oC)

5. Hot substances have high temperatures whereas cold substances have low temperatures

The differences between heat and temperature

Heat Temperature •is a form of energy •is the degree of hotness of

a substance•is measured in the joule (J)

•is measured in the kelvin (K)

•is the total amount of kinetic energy of the particles

•tell us how fast the particles are moving

HEAT FLOW AND ITS EFFECTExpansion and Contraction

1. Matter is made up of particles2. When matter is heated, the particles receive energy and

move faster. This causes the distance between particles to increase

3. The volume increases and the matter expands4. When matter is cooled, the particles lose energy and

move more slowly. The particles become closer to one another. The volume decrease and matter contracts

To study the heating and cooling effects on the volume of solids

Condition of metal ball observationHot Metal ball cannot pass through

the ringCold Metal ball passes through the

ring

Conclusion : A metal ball expands when heated and contracts when cooled

5. The summary about the expansion and contraction of matter shown in the chart below

HEAT FLOW

1. Heat can flow from one place to another2. It can flow in three different ways

- by conduction through solids- by convection through liquids or gases- by radiation through empty space

Conduction

1. When heat flows through solids, the process of heat transfer is called conduction

2. Conduction requires a medium for the heat energy to pass through

3. Heat passes through a metal rod when one end of it is heated in a flame.

4. Examples:-a) heat from a fire passes through the frying pan to

cook foodb) a metal spoon in the hand becomes warm after sometime because heat from the body passes to the metal spoon to warm itc) a chair becomes warm after a person has sat on it

for some time. Heat from the body passes to the chair to warm itd) the handle of a spoon becomes warm after some

time if the spoon is left in a cup of hot water. This means that heat from the water passes through

the spoon to the hand

Convection

1. Convection is the transfer of heat in fluids (liquids and gases) carried out by moving particles

2. Hot fluids become less dense and move upwards

3. Cold fluids that are denser move down to replace the hot fluids

4. An convection current is produced in this way

5. In the process of convection, heat is transferred upwards only

6. The fluids from hot areas move to cold areas

Radiation

1. Heat travels through empty space (vacumm) as radiation or heat rays

2. Heat rays are electromagnetic waves3. They travel very fast through space4. This is how heat from the Sun reaches the Earth5. All hot substances give out energy as radiation6. The radiation moves in every direction

Comparison between conduction, convection and radiation

Conduction Convection Radiation Medium for the process

Solid Fluid (liquid or gas)

Solid, liquid or gas

Takes place in vacumm

No No Yes

Speed Slow Faster than conduction

Very fast

Way heat transfer takes place

Heat is transferred from particles through vibration

Heat is brought by the heated particles that move upward

Heat moves in the form of waves in a straight line

Heat Flow in Natural PhenomenaLand breezes

1. Land breezes blow during the night2. At night, the land loses heat faster than the sea3. Thus, the land becomes cooler than the sea4. The warm air above the surface of the sea becomes less

dense and rises5. The air above the land that is denser (cooler) flows in

the direction of the sea, causing what is known as a land breeze

Sea breezes

1. Sea breezes blow during the day2. During the day, the land heats up faster than the sea3. As a result, the air on land becomes less dense and rises4. The cooler air over the sea which is denser (cooler)

flows in to take the place off the warm air, causing what is known as a sea breeze

The warming of the earth by the sun

1. The heat from the sun reaches the earth by radiation through a vacum in space (no medium)

2. The radiant heat which is absorbed heats up the earth

heat transmission

SUN EARTH

Heat Conductor

1. Substances that conduct heat are called conductors of heat

2. Some substances conduct heat readily. They are called good conductors of heat

3. All metals such as iron, magnesium, aluminium and zinc are good conductors of heat

The uses of heat conductors

The bottom of an electric iron is made of metals so that it can heat up quickly

1. Electric iron

•Cooking utensils such as kettles, pots and pans are made from metals like aluminium, copper and iron•Food can be cooked quickly or water can be boiled quickly

2. Cooking utensils

3. Thermometer

Mercury in the bulb expands and contracts quickly

1. Substances that conduct heat poorly are insulators or called bad conductors of heat

2. Non-metals such as glass, wood, cork, air, water and wool are insulators

Heat insulator

The uses of heat insulators

1. Igloo - Eskimos live in igloos- The heat in the igloo is constant because

ice is a poor conductor of heat

2. Glass rods – Glass rods are used to stir hot liquids

3. Handles of kettles, irons and cooking utensils- handles of kettles, irons and cooking utensils such as frying pans are made of wood, plastic or cork

EFFECT OF HEAT ON MATTER1. Matter exists in three states

i) solidsii) liquidsiii) gases

2. Matter can change from one state to another3. The change in states of matter involves the absorption

and release of heat4. The change in states of matter takes place through

physical processes such as:-- melting- boiling- freezing- evaporation- condensation- sublimation

1. MELTING

1. The solid particles absorb heat energy and vibrate faster in their positions

2. When they have absorbed enough energy, they will move freely from their positions to form a liquid

2. BOILING

1. The liquid particles absorb heat energy and move faster2. They also become further apart3. When they have absorbed enough heat energy, they will

move very fast and at random to form a gas4. The temperature at which a liquid start to boil is called

its boiling point

3. EVAPORATION

1. Evaporation is the process where a liquid changes into the gaseous state without heating

2. Heat is absorbed during the process3. Evaporation can take place at any temperature

4. CONDENSATION

1. The gas particles release heat energy to their surroundings

2. They move slower and closer until they form a liquid

5. FREEZING

1. The liquid particles release heat energy to the surroundings

2. They move slower and closer until they form a solid

6. SUBLIMATION

1. Sublimation is the process where a solid changes into the gaseous state without going through the liquid state when heated

2. Heat is absorbed during this process3. Sublimation is also the process where a gas changes into

the solid state without going through the liquid state when cooled

4. Heat is released during this process

sublimation

sublimation

sublimation

condensation

melting freezing

boiling / evaporation

sublimation

The changes in state of matter

Physical processes involved in the change in states of matter

Physical process

Change in state of matter

Heat absorbed

or released

Examples

Melting Solid Liquid Absorbed Ice melts to become water

Freezing Liquid Solid Released Water freezes to become ice

Boiling Liquid Gas Absorbed Water boils to become steam

Evaporation (A process where a liquid changes into the gaseous state without heating)

Liquid Gas Absorbed Water evaporates to become water vapour

Physical process

Change in state of matter

Heat absorbed

or released

Examples

Condensation Gas Liquid Released Steam condenses to become water

Sublimation (A process where a solid changes into the gaseous state without going through the liquid state)

Solid Gas

Gas Solid

Absorbed

Released

Dry ice sublimates to become carbon dioxide gas

Iodine vapour sublimates to become iodine crystals

Changes in the state of matter in everyday life

1. Ice melts at room temperature2. Water boils when heated3. Water freezes to form snow during winter in cold

climates4. Salt is formed from the evaporation of sea water5. Dry sublimates at room temperature6. When wet clothes dry in the sun, the water in the

clothes evaporate7. Water vapours in clouds condense to form rainwater

Applying the Principle of Expansion and Contraction of Matter

1. Mercury in thermometer

Mercury is a good heat conductorMercury expand evenly when heated and contracts

evenly when cooled

2. Bimetallic strip in a fire alarm

A fire alarm is used to warn of a fire taking placeWhen heated, the bimetallic strip expands and curves

towards the screw to complete the electrical circuitThe bell will ring to sound a warning

3. Rollers of steel bridges

Modern bridges are mostly of concrete and steelThe bridges expand on hot days and contract on cool

daysThe allow for movement when a steel bridge expands or

contracts, one of its end is fixed while the other end is free to move over rollers

This will prevent the bridges from bending and breaking up

4. Gaps in railway tracks

The gaps between the ends of rail tracks enable the iron tracks to expand on a hot day

The use of the principle of expansion and contraction of matter in solving simple problem

1. Bottle cap

Bottle cap that a tight can be loosened by immersing in hot water for a few minutes to make it expand

chapter 5 , 6, 7

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