CHEMISTRY TEXTBOOK

CHAPTER 4 EXPERIMENTS IN CHEMISTRY

Students book for 8th grades

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CONTENT

EXPERIMENTS IN CHEMISTRY ..................................................................................................... 2

4.1. WHAT IS AN EXPERIMENT? ................................................................................................... 2

Writing up experiments ........................................................................................................................ 3

4.2. Laboratory Safety Rules ................................................................................................................ 4

Hazard symbols .................................................................................................................................... 4

4.3. APPARATUS IN CHEMISTRY .................................................................................................. 5

The Bunsen burner ............................................................................................................................... 5

Instruments of measurement ................................................................................................................ 6

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EXPERIMENTS IN CHEMISTRY

What kind of equipment and skills do chemists need to carry

out experiments? Chemists find out about the nature of

substances by carrying out experiments in a laboratory.

Knowledge and understanding of the apparatus and skills

required for these practical investigations is an important

aspect of chemistry.

4.1. WHAT IS AN EXPERIMENT?

The experiment is the foundation of the scientific method,

which is a systematic means of exploring the world around

you. Although some experiments take place in laboratories,

you could perform an experiment anywhere, at any time.

The steps of the scientific method:

1. Make observations.

2. Formulate a hypothesis.

3. Design and conduct an experiment to test the

hypothesis.

4. Evaluate the results of the experiment.

5. Accept or reject the hypothesis.

6. If necessary, make and test a new hypothesis.

Observation is to collect information by using senses.

Observations can be qualitative or quantitative.

Qualitative observations describe properties or occurrences in

ways that do not rely on numbers.

The outside air temperature is cooler during the winter

season,

Table salt is a crystalline solid,

Sulfur crystals are yellow,

Dissolving a penny in dilute nitric acid forms a blue

solution and a brown gas.

Quantitative observations are measurements, which by

definition consist of both a number and a unit.

The melting point of crystalline sulfur is 115.210C,

35.9 grams of table salt—whose chemical name is sodium

chloride—dissolve in 100 grams of water at 200C.

Have you

wondered

chemical evidence

of the following

experiments?

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A hypothesis is a prediction of the outcome of a test. Good

hypothesis is testable, meaning it makes a prediction you can

check with observation or testing.

Not all hypothesis always may be true. For this reason the

following steps should be applied one by one so that, the truth

of the hypothesis will be proved.

If conditions of an observed event are known, can be

controlled and changed, this kind of observation is named as

experiment.

Chemistry is built up according to the results of the

experiment. It is important to record everything, which occurs

during the experiment.

Results should be written respectively, papers and tables must

be prepared to write the gained data.

Writing up experiments

Chemists should always plan their experiments and

investigations carefully. They must use scientific methods to

solve problems in chemistry. Most experiments will involve a

series of steps and these should be explained when writing up

the experiment.

The aim describes what you are trying to find out.

The method describes how the experiment is to be carried

out.

The result of the experiments should be recorded in a suitable

form.

The conclusion describes what you have found out.

INTERESTING FACTS

The ancient

Greeks, including

Aristotle and

Democritus, were

the first to

consider the

structure of

materials.

They did not do

experiments,

however, but tried

to find answers to

questions by

reasoned argument

alone.

They were

philosophers, not

scientists, and it

wasn’t until we

learned to use

experiments and

practical

investigations that

could properly

explain the nature

of substances.

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4.2. Laboratory Safety Rules

1. Do not enter the laboratory unless a teacher gives you

permission.

2. Never run or fool around in the laboratory.

3. Never eat or drink in the laboratory.

4. Never carry out experiments without your teacher’s

approval.

5. Before starting the experiment put all bags, jackets and

stools out of the way, and tie back loose hair or clothing.

6. Make sure you understand all instructions before you

start an experiment.

7. Wear eye protection during all experiments involving

heat or chemicals.

8. Always use small amounts of chemicals.

9. When heating a test tube point it away from people.

10. Report all accidents and breakages immediately.

11. Take your time: if you are not sure what to do, ask!

12. Clean and clear up all apparatus and leave the laboratory

as you found it.

The safety rules are only common sense. A chemistry

laboratory should be tidy and orderly environment. A place

to work and learn, not a place to play.

Hazard symbols

The substances used in a chemistry laboratory are safe if

used properly. However, certain chemicals can cause

particular problems, so they are labelled with hazard

symbols.

Figure 4.1. Hazard symbols.

DEFINITIONS

Corrosive:

substances, which

can burn and destroy

living tissue

Explosive:

Substances which

may explode if

heated, exposed to a

flame or knocked

Flammable:

Substances, which if

in contact with air,

may catch fire easily

Toxic:

Substances, which

represent a serious

risk of causing death

by poisoning

Harmful:

Substances, which

represent a

moderate risk to

health

Irritant:

Substances, which

can cause

inflammation of the

skin

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4.3. APPARATUS IN CHEMISTRY

The equipment used in a chemistry is called apparatus.

The Bunsen burner

The Bunsen burner (figures 4.2., 4.3.) produces a flame that

can be used for various purposes, such as heating or sterilizing

materials.

It is named after Robert Bunsen, not the scientist who

invented it, but the scientist who improved and popularized it

in the mid-1800s.

Parts and Diagram

A Bunsen burner is made entirely of metal. In order to

function properly, Bunsen burners must have a barrel (A)

that's approximately

five inches long, a

collar (B) with air

holes (C), a gas

intake (D) and gas

valve (E) and

a stand (F) to keep all

of the pieces from

making contact with a

work surface.

Figure 4.3.

Function

Once connected to a source of fuel, usually methane, the

Bunsen burner can be ignited with a spark. Incoming gas

reacts with oxygen in a one-to-three ratio to produce a blue

flame that comes out of the top of the barrel.

Adjusting the gas valve on the Bunsen burner changes the

volume of gas flow; the more gas entering the burner, the

larger the flame. The collar at the base of the barrel contains

air holes to control the amount of oxygen reacting with the

gas. The collar can be rotated to adjust oxygen intake. In

general, the more oxygen present, the more intense and blue

the flame will be. Less oxygen lends to a weaker yellow

flame. The more oxygenated blue flame is both hotter and

more controlled than the oxygen-deprived flame; scientists

generally prefer a controlled blue flame.

Figure 4.2. The

Bunsen burner

Figure 4.4. The

burner producing

two sets of blue

flames. The inner

flame is a smaller, a

brighter blue, while

the other flame is

larger, and a darker

blue. The flame is

hottest between

the tip of the

smaller flame and

the tip of the larger

flame.

The hottest part of

the Bunsen burner

is at the top of the

central cone, which

is formed when the

air hole is wide

open.

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Instruments of measurement

In many experiments, we have to measure quantities such as

mass, volume, temperature and time.

Measuring mass

A balance can be used to measure the mass of a substance.

There are many different types of balances, but the

commonest ones are electronic balances. (figure 4.5.)

The correct units for measuring mass are grams (g) and

kilograms (kg).

1 kilogram = 1000 grams

Figure 4.5. The electronic balance.

Measuring volume

The volume of a liquid is a measure of how much space it

takes up. There are several pieces of apparatus that can be

used for measuring volumes. The graduated cylinder is the

simplest is the simplest to use and can measure large volumes.

However, burettes and pipettes are more accurate, and

droppers can be used to measure small volumes of liquid.

Graduated glassware (burettes and graduated cylinders) is

used to deliver variable volumes of liquid.

Volumetric glassware is used to deliver (pipette) or contain

(volumetric flask) a single volume accurately when filled to

the calibration mark.

The correct units for measuring the volume of a liquid are

liters (l) and cubic centimeters (cm3)

1 litre = 1000 cubic centimeters

STUDY TIP

When measuring

out volumes, think

about the accuracy

required. A burette

or volumetric

pipette is far more

accurate than a

measuring cylinder.

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The scales on most graduated cylinders, burettes and pipettes

show the volume in cubic centimeters although some use

milliliters (ml). These units have the same value, that is:

1 cm3 = 1 ml.

Figure 4.6. Apparatus for measuring volumes of liquid.

In all volume measuring

devices, the surface of the

liquid curves upwards at the

edges and forms a meniscus.

When reading the scale on a

graduated cylinder you

should:

Place the cylinder on a

flat surface

Make sure your eye is

level with the surface of the

liquid

Read the scale at the

bottom of the meniscus.

Figure 4.7. Reading the meniscus.

STUDY TIP

How would you

measure the

volume of 1 drop

of water?

Add 100 drops of

water to a

graduated

cylinder and

measure the

volume. Divide

this volume by

100 and you

have the volume

of one drop.

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Measuring temperature

A thermometer can be used to measure temperature. There

are several different types of thermometer. The commonly

used in a chemistry laboratory are the alcohol in glass

thermometer and the mercury in glass thermometer.

Figure 4.8. The alcohol in glass thermometer

Temperature is measured using the Celsius scale, which is

based on the temperatures at which water freezes and boils.

The correct units for measuring temperature are degrees

Celsius (0C).

To measure the temperature of liquid correctly, totally

immerse the bulb of the thermometer and leave it for a minute

or two before reading the scale. Do not take the thermometer

out of the liquid to read the scale.

In table 4.1 some laboratory equipment and their uses is

given.

KEY POINTS

In chemistry, mass is

measured in grams,

temperature in 0C

and volume in cm3.

The apparatus you

select for an

experiment depends

on the accuracy

required in your

experiment.

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Goggles

Защитные

очки

Protects eyes from

chemical splashes

Bunsen

burner

(Alcohol

burner)

Cпиртовка

Used to heat substances

Graduated

cylinder

Мерный

цилиндр

To measure exact

volume of liquid

Spot plate

Пластинка с

лунками

A flat plate with

multiple "wells" used as

small test tubes

Pipet bulb

Пипетка

Used to pull liquid up

into a pipet

Stirring rod

Стеклянные

палочки

Used for stirring

Evaporating

dish

Фарфоровая

чашка

Liquids are heated over

a flame so that they

evaporate, leaving a

solid residue

(for crystallization)

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Crucible

tongs

Тигельные

щипцы

To hold hot crucibles

Forceps

Пинцет

Used to pick up or hold

small items

Watch glass

Часы стекло

To hold solids while

being weighed, or as a

cover for a beaker

Beaker

Химический

стакан

Used to hold liquids

Thermometer

Термометр

Measures temperature

(science uses degrees in

Celsius)

Crucible

and cover

Тигель и

крышка

Used to hold small

amounts of chemicals

during heating at high

temperatures

Test tube

clamp

(holder)

Пробирко-

держатель

Сlamp used to hold hot

test-tube

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Buret

Бюретка

Dispensing and

transferring known

volumes of fluids

Balance

Весы

An instrument for

determining weight

Dropper

pipet or

disposable

pipet

Пипетка

химическая

For drawing in a liquid

and expelling it in

drops

Volumetric

flask

Мерная колба

For making up

solutions to a known

volume

Funnel

Воронка

For pouring liquid or

other substance through

a small opening

Utility

clamp

Зажим

Used to hold laboratory

glassware

Mortar and

pestle

Фарфоровая

ступка с

пестиком

Used to grind up

materials

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Volumetric

pipet

Мерная

пипетка

Measures small

amounts of liquids

accurately

Rubber

stopper

Резиновая

пробка

Used to cover ends of

test tubes and flasks

Spatula Шпатель

Small scoop used to

transfer powder and

crystal chemicals

Wire gauze Асбестовая

сетка

Used to support a

container (such as a

beaker or flask) during

heating

Test tube rack Штатив для

пробирок

Holds 5-6 test tubes in a

row

Wash bottle Бутылка для

мытья

Used to rinse various

pieces of laboratory

glassware

Erlenmeyer

Conical

flask

Коническая

колба

Эрленмейера

Used to hold liquids,

has narrow neck to

prevent splashes

Ring clamp Кольцо

зажим

Used with ring stand

to hold a glass

container

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Test tube Пробирка

Open tube used to

hold liquids

Filter paper Фильтроваль

ная бумага

Special paper used to

separate solids from

liquids

Fume hood Вытяжной

шкаф

Used to prevent a

person from exposure

to hazardous fumes

from chemicals

Clamp

stand

Штатив

лабораторный

To hold and fix

laboratory equipment

Table 4.1. Some equipment used in chemistry laboratory.