Class 6 Times Science

This is due to evaporation of water
from the washed clothes.

3. Water in the river comes from
melting of snow of Himalayas.
Melting of snow is due to the
heat from the sun.

4. Metals are melted into liquid
by heating them and changed
into different shapes. Thus, ornaments, statues, etc are made
from metals.

Element and compound

Some substances are composed of only one type of atoms whereas
other substances are composed of two or more types of atoms. The
substances which are composed of only one type of atoms are called
elements. Nitrogen, oxygen, hydrogen, calcium, iron, etc are examples
of elements. There are 118 elements discovered so far. Out of them, 92
elements are found in nature and 26 elements are produced articially
in laboratories. Elements are found in three states, i.e. solid, liquid
and gas. Element like bromine, mercury, caesium, francium and
germanium are found in liquid state. Eleven elements are found in
gaseous state. Nitrogen, oxygen, hydrogen, etc are some examples.
Rest of the other elements are found in solid state. Based on the
properties, elements are further divided into metal, non-metals and
metalliods.

Metals

The elements which conduct heat and electricity are called metals.
For example, iron, aluminium, copper, etc.

NThoen-emleemtaelnsts which cannot conduct heat and electricity are called

non-metals. For example, carbon, phosphorus, oxygen, hydrogen,
nitrogen, etc.

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Metalloids

The elements which are poor conductors of heat and electricity are
called metalloids. For example, silicon, germanium, arsenic, etc.

The substances which are composed of two or more types of atoms are
called compounds. Since, compounds contain two or more types of
atoms, they can be further divided into other substance. For example,
water, carbon dioxide, sodium chloride (salt), etc are compounds.

Water is composed of atoms of hydrogen and oxygen. It can be divided
into hydrogen and oxygen.

Differences between element and compound

Element Compound

1. It is a type of substance which 1. It is a type of substance which

is composed of only one kind is composed of two or more

of atoms. kinds of atoms.

2. It cannot be further divided 2. It can be further divided into

by chemical method. its components by chemical

method.

3. Examples: oxygen, nitrogen, 3. Example: water, carbon

iron, aluminium, etc. dioxide, ammonia, etc.

Mixture

When two or more non-reacting substances are kept together, mixture
is formed. During the formation of mixture, mixing substances do not
lose their properties. For example, when we mix sugar and sand,
they do not lose their properties. They remain together only but do
not undergo chemical change. Thus, mixture of sugar and sand is
formed. The mixing substances are called components of mixture.
Here, sand and sugar are components of mixture. They can be mixed
in any proportion.

Thus, mixture is a substance which is formed by mixing two or more
substances in any proportion by weight.

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Main Points to Remember

1. Any substance which occupies space and has mass is called matter.
2. Solid, liquid and gas are three states of matter.
3. Molecules are small particles of a substance which can exist

freely and contain all properties of the substance.
4. Atoms are the smallest particles of matter by which

molecules of such matter are composed.
5. The substance which is composed of only one type of atoms

is called element.
6. The substance which is composed of two or more types of

atoms is called compound.
7. The substance which is formed by mixing two or more

substances in any proportion by weight is called mixture.
8. The process of changing of solid into liquid on heating is

called melting.
9. The process of changing of liquid into gas on heating is

called evaporation.
10. The process of changing of liquid into solid on cooling is

called solidication or freezing.
11. The process of changing of gas into liquid on cooling is called

condensation.
12. The process of changing of solid into vapour on heating and

vapour back to solid on cooling is called sublimation.

Exercise

1. Choose the best alternative in each case:

a. Which of the following sentences is incorrect about matter?

i. Matter has mass.

ii. Matter occupies space.

iii. Matter is made of atoms or molecules.

iv. Matter can be seen.

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b. The smallest particle of matter which can take part in a
chemical reaction is called

i. Molecule ii. Atom

iii. Particle iv. All of these

c. The process of change of a liquid substance into its solid form
is called

i. Melting ii. Evaporation

iii. Freezing iv. Condensation

d. Sublimation occurs in ii. Iodine
i. Camphor iv. All of these
iii. Ammonium chloride

e. How many elements have been discovered so far?

i. 109 ii. 118

iii. 112 iv. 92

2. Copy the correct statements and correct the wrong
statements if any:

a. Matter is any thing which has mass, volume and occupies space.
b. Solid is a form of matter in which molecules are tightly

packed.
c. Intermolecular force is more but intermolecular space is less

in solid than in gas.
d. The process of changing solid into liquid on heating is called

solidication.

e. The process of changing solid into vapour on heating and
vapour back into solid on cooling is called sublimation.

f. Rain occurs due to change in state of matter.

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3. Answer these questions in short:

a. What is matter? Mention three states of matter.

b. What is element? Give any four examples.

c. What is compound? Give any four examples.

d. Dene

i. atom ii. molecule iii. melting

iv. solidication v. condensation vi. evaporation

e. What is sublimation? Mention examples of two substances
which show sublimation process.

4. Differentiate between:

i. Element and compound
ii. Atom and molecule
iii. Melting and solidication

iv. Evaporation and condensation

5. Answer in detail:

a. How can you prove that air is a matter?
b. How are molecules arranged in solid, liquid and gas? Show

with diagrams.
c. Explain evaporation and condensation process with diagrams.
d. Explain the process of sublimation with the help of diagram.
e. What are various uses of change in state of matter?

Project Work

Take a beaker and put pure water in it. Put little sugar in the
water and dissolve it. What do you nd? Put little salt in the
same water and dissolve it. Taste the mixture. What do you nd?

You can feel the taste of sugar only in the rst case. In the second
case, you can feel the taste of sugar and salt both

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Chapter

10 MIXTURE

Estimated periods: 5

OBJECTIVES
At the end of the lesson, the students will be able to :

Ü dine the pure and impure substances;
Ü dene mixture and classify it into different types;
Ü explain the methods for the separation of different mixtures.

MIND OPENERS
Ü What do you mean by pure and impure substances?
Ü Are the impure substances useful to us?
Ü Can we separate the components of a mixture?
Ü How do you separate rice from husk?
Ü Observe different substances around you and discuss about their

composition.

Introduction

Different things are made of different substances. For example, chair,
table, desk, window, door, book-shelf, etc are made of wood. Book,
copy, paper, magazines, newspapers, etc are made of paper. Similarly,
bucket, bag, raincoat, etc are made of plastics. Wood, paper, plastics,
water, soil, salt, sugar, iron, etc are called substances. The substances
have denite properties and composition. For example, water and oil
are two different substances. They have their own properties. Some of
their properties are similar while some are dissimilar. Both of these
are liquids, hence they have same state. But, water can dissolve salt
in it whereas oil cannot. Water does not have its smell and colour.
But oil has its own smell and colour.

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Pure and impure substances

The substances which are made of only one kind of atoms or molecules
and have denite composition and properties are called pure
substances. Gold, silver, copper, hydrogen, oxygen, carbon dioxide,
water with no dissolved gases and salts, etc are some examples of
pure substances. The water that we use is usually impure because
it contains dissolved oxygen gas, salts, minerals, etc. Rain water is
considered as the purest natural form of water. In fact, it may not be
pure because it may contain dust particles and dissolved gases due
to air pollution.

The substances which are made up of two or more kinds of molecules
and do not have denite composition and properties are called impure
substances. The mixtures are the impure substances. For example,
air, water from natural sources, jelly, fruit juices, cold drinks, tea,
etc are some impure substances. Milk is also an impure substance
because it is a mixture of fat and water.

We need both pure and impure substances in our daily life. Sometimes
impure substances may spoil our health. For example, dirty air and
water (which are impure) can transmit diseases. But, it doesn’t mean
that impure substances are necessarily harmful for health. We use
many things in the form of mixtures. For example, our foods, milk,
tea, medicines, etc are the mixtures or impure substances.

Mixture

A mixture is formed if we mix two or more substances together. A
mixture is an impure substance.

Activity 10.1
To prepare mixtures of different substances

Materials required: Common salt, sand, cooking oil, water, beakers,
spoon, etc

Procedure

1. Take three clean beakers, ll half of them with clean water
and label them as I, II and III respectively.

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2. Add a spoonful of common salt in the beaker I, a spoonful of
sand in beaker II and two spoonfuls of cooking oil in beaker III.

3. Stir each beaker with the help of a separate spoon and leave
them undisturbed for some minutes.

Observation: You have prepared three different mixtures. In beaker
I, the common salt completely disappears in water to make a mixture.
But in beakers II and III, the substances do not get disappeared.
They just lie together.

Conclusion: Mixtures are formed when we mix two or more
substances together.

A mixture is an impure substance which is formed by mixing two
or more substances in any proportion by weight. The properties of a
mixture depend upon the properties of individual components. The
substances which are mixed to form a mixture are called components
of a mixture. Sand in water, common salt in water, oil in water, cold
drink, tea, etc are some examples of mixtures.

Types of mixtures

The mixtures can be divided into two types on the basis of physical
state of the components. They are: homogeneous mixture and
heterogeneous mixture.

1. Homogeneous mixture

If you add a spoonful of sugar in a glass of water and stir it, the sugar
dissolves in water. In this process, the sugar molecules are uniformly
distributed in water and they cannot be seen with our naked eyes.

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We can see only water in the glass, i.e. the solid state of sugar has
got lost in water and we can see only the liquid state. The mixture,
thus obtained, is called homogeneous mixture.

A mixture of two or more substances in which one component
completely disappears in another is called homogeneous mixture. In
such mixture, the particles of the solute are uniformly distributed in
the solvent and cannot be seen with the naked eyes. A homogeneous
mixture is also known as solution. For example, brine (salt solution),
syrup (sugar solution), alcohol in water, soda water, fruit juice, etc
are the examples of homogeneous mixtures.

Solution

A solution is a homogeneous mixture of two or more substances. In
other words, it may be dened as the homogeneous mixture of solute
and solvent. The size of the particles of the components in solution
is 10-7cm or less.

Solvent + Solute = Solution

Examples: Brine (a solution of salt in water), syrup,
vinegar, etc. In brine, common salt is a
solute as it gets dissolved in water and
water is a solvent because it dissolves
the solute.

2. Heterogeneous mixture

A mixture of sand and water is an example of heterogeneous mixture.
In this mixture, two states of substances are seen. The sand does
not get dissolved in water and remains in solid state whereas water
remains in liquid state. The sand particles can be seen with our
naked eyes.
Hence, a mixture of two or more substances in which the particles of
the components are not uniformly distributed and can be seen with
naked eyes is called heterogeneous mixture. Some common examples
of heterogeneous mixture are: muddy water, smoke, husk in rice
grains, sand and salt, etc.

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Suspension

A suspension is a heterogeneous mixture in which the size of the
particles is 10-5 cm or bigger. The particles are visible to naked eyes.
If not so, they can be seen with a simple microscope. Some examples
of suspension are: mixture of sand and water, muddy water, mixture
of saw dust and water, etc.

The solid particles of a suspension settle down at the bottom of the
containing vessel on long standing. You must have seen a sentence
“Shake well before use” written on the bottle of medicine. It is because
many medicines are used in the form of suspension and the medicine
particles settle down on long standing. If the bottle is shaken well,
the medicine particles are equally distributed in the solvent and it
works properly in the body.

Colloids

A colloid is a uniform mixture in which the diameter of the particles
ranges between 10-7cm to 10-5cm. The components of colloid do not
settle down even on long standing. Some examples of colloid are:
blood, milk, gum, etc.

Separation of a mixture

We use many things in the form of mixture. But all the mixtures
are not useful. Sometimes, we need some substances in pure state.
Hence, we have to separate the components of a mixture so that we
obtain individual component in pure state.

Similarly, we separate some mixtures to remove useless substances
from the useful substances. We separate the components of different
mixtures using different methods.

The process by which the components of a mixture are separated
from each other is called separation of mixture. The separation of a
mixture can be done on the principle that “different substances have
different properties”.

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Methods of separation

We use different methods to separate the components of different
mixtures. The choice of the method depends on the nature and
composition of the mixture. Some common methods for the separation
of mixture are discussed below.

Using a winnowing tray (Nanglo or Supo)

A winnowing tray is a circular concave disc which is made by weaving
the thin bamboo sheets. It is raised from the circumference so that it
can hold food grains inside it.

Activity 10.2

To prepare and separate the mixture of wheat grains and peas

Materials required

About 1 kg wheat grains, 200 grams peas and a winnowing tray.

Procedure
1. Mix about one kilograms of wheat
grains and about 200 grams of
peas in a winnowing tray.
2. Lift the winnowing tray little up
using both hands.
3. Move the tray right and left (in to and fro way) so that the
grains slide one over another.

Observation

The peas being round and smooth roll forward while moving the tray.
The wheat grains remain on the back position in the winnowing tray.

Conclusion

The pea seeds can roll whereas the wheat grains cannot. So, such
mixture can be separated using a winnowing tray. But it is difcult
to separate rice and wheat grains by this method.

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Winnowing

Winnowing is a process of
removing lighter things from
the heavier things. This process
is used to separate ne rice
grains from the husk or coarse
rice grains from husk while
harvesting.

If systematic jerks are provided
to the winnowing tray, the
mixture of rice grains and husk moves up. In this process, the lighter
husk is blown away by the air but rice grains remain in the winnowing
tray. We can separate rice grains from husk in large scale during
harvesting. In this process, the energy of the wind is also used.

Sieving

A sieve is a vessel which has tiny holes at
its bottom. Generally, a ne net is used on
the bottom of a sieve. The process of using a
sieve to separate the components of a mixture
is known as sieving. If the components of a
mixture differ in the size of the particles,
the sieving method is used to separate them.
Sieving is usually done to separate ne wheat
our from unground wheat grains and other
unwanted particles.

Sedimentation and decantation

Sedimentation and decantation are used to remove the suspended
impurities such as sand, mud, etc from the mixture. These two
processes are carried out one after another. At rst, the process of
sedimentation of the suspension is done and then decantation.

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Activity 10.3
To separate the mixture of sand and water
Materials required

Two beakers, a glass rod, a mixture of sand and water, etc.

Sedimentation Decantation

Procedure

Take a mixture of sand and water in a beaker and stir it with a glass
rod. Then remove the glass rod and leave the mixture undisturbed
for 5-10 minutes.

Observation

The sand particles settle down at the bottom of the beaker. The clear
water forms the upper layer.

Conclusion

Suspended heavier impurities can be separated by settling down at
the bottom of the vessel.

In the above activity, the process of settling down of the heavier
and insoluble particles of a mixture is called sedimentation. After
sedimentation, the clear water can be poured into another beaker
without disturbing the settled sand. This process is called decantation.
Hence, the process of transferring the clear liquid without disturbing

the settled insoluble impurities is called decantation.

Filtration

This method is used to separate the very ne particles of an insoluble
solid from a liquid. It can also be used to separate the mixture of two

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solids in which one is soluble in water
and the other is not. In this method,
the mixture is poured slowly over
a ltering material such as cotton
cloth, lter paper, glass wool, ltering
candle, etc. When the mixture is
poured over a ltering material, the
liquid part of the mixture passes
easily through it but the insoluble
solid particles remain collected on the ltering material. Thus, the
process of separating an insoluble solid from a liquid by using a
ltering material is called ltration.

We use the process of ltration at our home to clean our drinking
water. A water lter is used at our home which lters water with a
ltering candle. Similarly, we separate tea particles from tea using a
strainer or a tea lter. In country areas, people use a thin cotton cloth
to lter water. Similarly, in the science lab, we use a lter paper to
separate the components of sand and water, muddy water, etc.

Activity 10.4

To separate the mixture of sand and water

Materials required

A beaker, lter paper, funnel, stand, a glass rod, mixture of sand and
water, etc.

Procedure

1. Take a mixture of sand and water in a beaker.

2. Take a piece of lter paper and fold it to make two equal halves
so that you get a semicircle. Again fold the semicircle into two
equal halves so that you get a triangle.

3. Now, open the lter paper by lifting one sheet alone from three
others. You will get a cone shaped lter paper.

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4. Wet the outer walls of lter paper by sprinkling some pure
water and t it in a funnel.

5. Adjust the funnel just above a clean beaker with the help of a
funnel stand. The lower end of the stem of the funnel should
touch the inner wall of the beaker.

6. Hold a glass rod against the inner wall of the funnel and pour
the mixture of water and sand gently on it. The lter paper can
rupture if you pour water directly into it. So, we use a glass rod.

Observation:

Only water passes through the lter paper whereas the solid
substances remain over the lter paper as residue. Hence, we obtain
clear water in a beaker.

Conclusion: The lter paper has very small pores through which
water can pass easily but solid substances cannot pass. Hence, solid
substances remain on the lter paper and we can separate such
substances.

The solid substances which remain on the lter paper after ltration
is called residue. In the above case, sand is the residue. The clear
liquid obtained on a clean pot after ltration is called ltrate. In the
above case, the clean water obtained in the beaker is ltrate.

Evaporation

The process of converting liquids into vapour by heating is called
evaporation. It is one of the methods of separation of mixture. We
can separate salt from its aqueous solution by this method.

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Activity 10.5

To separate salt from a solution of salt and water

Materials required

A solution of salt and water, porcelain basin, tripod stand, wire
gauge, burner, etc.

Procedure

1. Prepare a salt solution by adding one Vapour
spoonful of salt in 500 ml water in a
beaker. Porcelain
basin
2. Fill about half of a porcelain basin (an
earthen pot) with the salt solution. Burner
Tripod
3. Heat the porcelain basin with Bunsen stand
burner by placing it over wire gauze.

Observation

Water evaporates on heating. When whole of the water gets converted
in to vapour, only salt remains in the porcelain basin.

Conclusion: Water evaporates even at low temperature. When the
temperature is increased, it evaporates faster leaving salt in the
porcelain basin.

We can obtain only solid after evaporation because the liquid ies
away as vapour. Hence, we cannot get both the components of a
solution by evaporation. There is another process called distillation
by which we can separate a solution into its components. In this
method a solution is heated in a closed vessel having a side tube.
When the mixture is heated, water gets converted into vapour and
travels along the side tube. The side tube is cooled using cold water.
The cold water converts the vapour into water which is collected in a
receiver. Finally, we obtain solid substance in the closed vessel and
water in the receiver. Thus, we can separate a mixture.

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The process of conversion of liquid into vapour by heating and the
vapour into liquid state again by cooling is called distillation.

Magnetic separation

The process of separating magnetic substances from non-magnetic
substances with the help of a magnet is called magnetic separation. If
there are pieces of magnetic substances such as iron, cobalt, nickel,
etc in the mixture, they are easily removed by attracting on a magnet.
This process is called magnetic separation.

Main Points to Remember

1. We use several substances in our daily life.

2. The substance which is made of only one kind of particles
and has denite composition and properties is called pure
substance.

3. The substance which is made of more than one kind
of particles and doesn’t have denite composition and
properties is called impure substance.

4. A mixture is an impure substance which is formed by placing
two or more substances together in any proportion by
weight.

5. A mixture can be divided into two types-homogeneous
mixture and heterogeneous mixture.

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6. A mixture of two or more substances in which one component
completely disappears in another is called homogeneous mixture.
7. A mixture of two or more substances in which the particles

of the components are not uniformly distributed and can be
seen with naked eyes is called heterogeneous mixture.
8. Suspension is a heterogeneous mixture in which the size of
the particles is 10-5 cm or bigger.
9. A colloid is a uniform mixture in which the diameter of the
particles ranges between 10-7cm to 10-5cm.
10. The process by which the components of a mixture are
separated is called separation of mixture.
11. The mixtures are separated on the principle that different
materials have different properties.
12. Winnowing, sieving, sedimentation, decantation, ltration,
evaporation, distillation, magnetic separation, etc are some
common methods used in the separation of mixtures.

Exercise

1. Choose the best alternative in each case:

a. Which of the following is a mixture?

i. Water ii. Hydrogen iii. Air iv. Iron

b. Which of the following is a mixture?

i. Tea ii. Milk

iii. Sugar solution iv. All of the above

c. An example of heterogeneous mixture

i. Muddy water ii. Brine

iii. Syrup iv. All of the above

d. Which of the following is a colloid?

i. Blood ii. Milk iii. Gum iv. All of these

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e. Fine wheat our is separated from unground wheat grains and
other unwanted particles by

i. Winnowing ii. Filtration
iii. Sieving iv. Decantation

2. Answer these questions in very short:

a. What is a substance?
b. Are impure substances always harmful?
c. Give any two examples of pure substances.
d. Name any two solids that are soluble in water.
e. Is milk a pure substance? If not, why?
f. What is the size of particles in a solution?
g. Name the method suitable to separate the mixture of rice and

husk.

h. What is a sieve?

3.Write down the method of separation for the following
mixtures:

a. Sand and water
b. Rice grains and husk
d. Iron llings and sugar
e. Soil and water
f. Common salt and water
g. Wheat grains and husk

h. Rice and pea seeds

4. Separate the pure and impure substances:
Water from a river, wheat our, cold drink, sugar, gold, copper,
soil, ne rice grains, brine

5. Separate the homogeneous and heterogeneous mixtures:
Water and kerosene, water and alcohol, water and salt, water and
sand, sand and sugar, kerosene and petrol, oil and water, oil and
salt, milk, gum, blood, syrup

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6. Name the following:

a. Two liquids that are soluble in water.
b. A liquid that is insoluble in water but burns.
c. Solid substance that remains on lter paper after ltration.
d. A bamboo tray used to separate rice from husk.
e. Two types of mixtures.
f. Two types of heterogeneous mixtures.
g. Components of brine.

7. Give reasons:

a. We have to separate the mixtures.
b. All impure substances are not harmful.
c. A mixture of iron llings and sand can be separated by using

a magnet.
d. A sentence “shake well before use” is written on the bottle of

medicine.

8. Dene the following:

a. Solution b. Residue c. Filtrate
f. Filtration
d. Sedimentation e. Decantation i. Winnowing

g. Suspension h. Colloid

9. Write down differences between:

a. Homogeneous mixture and heterogeneous mixture
b. Suspension and solution
c. Residue and ltrate
d. Pure and impure substances

10. Answer these questions:

a. Describe the process of ltration to separate the mixture of
sand and water.

b. What is a homogeneous mixture? Give examples.
c. Describe the process of sedimentation and decantation.

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d. What is distillation? How is it different from evaporation?
e. Write down short note on heterogeneous mixture.

11. Diagrammatic questions:

a. Draw a neat and labelled diagram of the process of
sedimentation and decantation.

b. Draw a neat and labeled diagram of the process of ltration.

c. Study the diagram and answer the A
questions: B
i. What is shown in the gure?

ii. Label the parts A, B and C. C
iii. Name any two mixtures that can

be separated by this process.

Project Work

Prepare different mixtures by mixing two or more substances
in each case. Then choose a suitable method to separate these
mixtures. If you cannot separate any of the mixtures, you can
take help of your teacher.

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Chapter

11 AIR

Estimated periods: 6

OBJECTIVES
At the end of the lesson, the students will be able to :

Ü dene air as the mixture of gases;
Ü tell and explain physical and chemical properties of air;
Ü explain about the main gases of the air and their importance.

MIND OPENERS
Ü Can you see air? How can you say that there is air around us?
Ü What are the components of air?
Ü What are physical properties of air?
Ü Why is air important?

Introduction

Our earth is surrounded by air. We cannot see the air but we can
feel its movement. The movement of leaves of plants, ying away of
clothes due to wind, etc show the presence of air.

Air is very important for living things. It contains various gases
which are essential for living things. These gases occupy following
percentage of total volume of air.

Gas Percentage by volume

Nitrogen 78.1%

Oxygen 20.9%

Carbon dioxide 0.03%

Inert gases 0.95%

Other gases 0.02%

Composition of air remains almost the same in all places. But it
differs in some places. The amount of carbon dioxide and water
vapour differs from place to place.

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Nitrogen occupies 78.1% of the total volume of air. In the same way,
oxygen occupies 20.9% of the total volume. Carbon dioxide occupies
0.03% of the total volume of Air. Except these gases, there are
other gases like inert gases, water vapour, sulphur dioxide, carbon
monoxide etc. Gases like helium, argon, neon, krypton, etc do not
take part in chemical reaction. These gases are called inert gases.

Oxgen
It is one of the most important gases present in the air. It occupies
20.8% of the total volume of air. It is life gas for living things because
living things cannot survive without oxygen. All living things use
oxygen for breathing. Oxygen is used for burning of rewood, petrol,
diesel, coal, etc to produce heat energy. Oxygen is used to carry out
various types of chemical reactions. Oxygen in cylinder is used for
the treatment of serious types of patients. Mountaineers take oxygen
cylinder to breathe in higher altitude.

Activity 11.1

To prove that air contains water vapour

Materials required: A candle, a plate, big vessel, bell jar, etc.

Procedure

1. Take a candle and x it on a small plate.

2. Keep a plate over water kept in a bigger vessel.

3. Burn the candle and cover it with a bell jar and cover its
mouth. What happens?

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Observation: The ame of the candle becomes smaller and at last
it gets extinguished. When the candle gets extinguished, the water
level increases slightly inside the bell jar.

Conclusion: Here, when the candle burns inside the bell jar, all the
oxygen inside the bell jar is used up for burning. The water from the
vessel goes upward to the bell jar to occupy the place of the oxygen.

Now, place a burning splinter inside the same bell jar. The splinter
gets extinguished due to absence of oxygen. This experiment proves
that air contains oxygen.

Carbon dioxide

Carbon dioxide occupies 0.03% of the total volume of air. It is heavier
gas. It is mostly found in large amount in the caves, deep well, and
in lower altitude.

Carbon dioxide is used by plants for the preparation of food during
photosynthesis. Animals depend upon plants for food. Carbon dioxide
is used in some drinks like coca-cola, sprite, beers etc. Carbon dioxide
is used as re extinguisher (for putting out re). You must have seen
cylinders of carbon dioxide kept in hospitals, schools, ofces, etc for
emergency use.

Activity 11.2

To prove that air contains carbon dioxide

Materials required: A beaker, hand pump and lime water

Procedure

1. Take a beaker and put a little lime water in
the beaker.

2. Pump air inside the lime water with the
help of the hand pump as shown in the
gure. What will you observe?

Observation: The lime water slowly turns into milky colour.

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Conclusion: The change in colour of lime water to milky colour is
due to carbon dioxide present in the air.

Water vapour

We dry wet clothes by keeping them in the sun shine. Similarly,
drying of lakes and ponds occurs in summer and winter season.
Here, water from the wet clothers, lakes and ponds evaporates and
moves towards the atmosphere. Thus, water vapour is present in
air. The water vapour gets condensed from the atmosphere due to low
temperature and falls to the earth surface in the form of rain. Fog and
mist are also the examples of water vapour. The amount of water
vapour present in the air is called humidity.

The water vapour present in the atmosphere prevents the drying out
of leaves of plants as well as fruits and owers. It protects the skin of
animals from drying.

Rusting

When you keep an iron nail in a moist place for some days, you will
notice the turning of the iron into reddish brown colour. It is called
rusting. It is due to the reaction of iron with oxygen in the presence
of water vapour and formation of iron oxide. This iron oxide is called
rust. Thus, the process of formation of rust by the slow oxidation of
iron in the presence of water vapour and oxygen is called rusting.

Activity 11.3

To prove that air contains water vapour

Materials required: A glass, ice cubes, etc.

Procedure

1. Take a glass and put some ice cubes in the
glass.

2. Leave it for 10 minutes. What will you
observe?

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Observation: After some time, you can see the drops of water on the
outer surface of the glass.

Conclusion: Drops of water on the outer surface of the beaker is due
to the condensation of water vapour present in the air. Formation of
dews on the leaves of plants in the morning is due to the condensation
of water vapour present in air.

Insert gases

Gases like helium, neon, argon, etc are found in the air in less amount.
They do not react with other substances. Therefore, they are called
inert gases. They occupy 0.95% of the total volume of air.

Properties of air

Physical properties of air

a. Air is colourless so that it cannot be seen with naked eyes.
b. Air is a mixture of different gases such as nitrogen, oxygen,

carbon dioxide, inert gases, water vapour, etc.
c. Air has weight.
d. Air ows from one place to another.
e. Air occupies space.

Chemical properties of air

a. Metals like iron get rusted due to reaction of the metal with
oxygen and water vapour present in the air.

b. Various substances like petrol, rewood, diesel, etc burn with
oxygen present in air. Burning means reaction with oxygen.

Main gases of air

Nitrogen, oxygen, carbon dioxide, inert gases, etc are the main gases
present in the air. These gases are important to living things.

Nitrogen

Volume of nitrogen in the air is 78% of total volume of air. It is lighter
gas. Nitrogen is used by plants for the preparation of protein. But
the plants cannot use the atmospheric nitrogen directly. Some plants

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like soyabean, bean, gram, etc can absorb nitrogen directly by their
roots from air.

The protein prepared by the plants is used by animals too. Protein
is one of the main foods of plants and animals. Nitrogen is used by
human beings to prepare various types of chemicals like ammonia,
chemical fertilizers, etc. Nitrogen gas is used inside lament lamp.

Main Points to Remember

1. Air is the mixture of various gases.
2. Air contains mainly nitrogen (78.1%), oxygen (20.98%),

carbon dioxide (0.03%) and inert gases (0.95%).
3. Nitrogen is used by plants for the preparation of food.
4. Oxygen is used by living things for breathing. It is used for

burning rewood, petrol, diesel, etc.
5. Carbon dioxide is used by green plants for the preparation

of food during photosynthesis.

Exercise

1. Choose the best alternative in each case:

a. Which is the most abundant gas present in air?

i. Oxygen ii. Carbon dioxide

iii. Nitrogen iv. Argon

b. What is the percentage of carbon dioxide in the atmosphere?

i. 78% ii. 21% iii. 0.95% iv. 0.03%

c. The process of slow oxidation of iron due to the action of water
vapour and oxygen is called

i. Reaction ii. Burning

iii. Rusting iv. Humidity

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d. Name the gas which is lled in a lament lamp.

i. Neon ii. Water vapour

iii. Hydrogen iv. Nitrogen

e. Which of the following is incorrect?
i. Air is a mixture of different gases.
ii. Air does not have weight.
iii. Air occupies space.
Iv. Air blows from one place to another.

2. Copy the correct statements and correct the false statements
if any:

a. Air is a mixture of different gases.
b. Nitrogen occupies 71% of total volume of air.
c. Helium, argon, nitrogen, and neon are inert gases.
d. Burning of rewood, petrol, diesel, etc is possible due to

carbon dioxide.
e. Carbon dioxide is mostly found in deep places like caves, well, etc.
f. Nitrogen is used by animals for the preparation of protein.

3. Answer these questions in short:

a. What is air? What are the main components of air?
b. Mention the composition of air.
c. Mention any four properties of air.
d. Mention any two uses of nitrogen.
e. Mention any three uses of oxygen.

4. Answer in detail:

a. How can you prove that air contains oxygen?
b. How can you prove that air contains carbon dioxide?

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c. Explain an activity which shows that air contains water
vapour.

d. Why does metal like iron get rusted?

e. Mention the chemical properties of air.

Project Work

Take a beaker and ll it half with water. Take a test tube and put
a little steel wool in the test tube. Make the steel wool moist by
putting few drops of water. Invert the test tube and put over the
water of beaker. Mark the level of water in the test tube. Put the
apparatus for 2 days without disturbing. What will you observe?

You can see the rusting of the steel wool. The level of the water
in the test tube rises. This is because the oxygen of the test tube
is used during rusting and water rises to the test tube to take the
space of oxygen.

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Chapter

12 METAL AND Estimated periods: 8
NON-METAL

OBJECTIVES
At the end of the lesson, the students will be able to :

Ü give general introduction of metals and non-metals;
Ü explain the uses of metals and non-metals in daily life.

MIND OPENERS
Ü What utensils are being used at your home? Name them.
Ü What are these utensils made of? How are they made?
Ü Can you make a ne plate by beating a stone? Discuss.

Introduction

Matter is anything that has mass and occupies space. The matter is
composed of either element, compound or their mixture. An element
is the pure substance that is made of similar kinds of particles. There
are altogether 118 elements discovered so far. These elements can be
categorized into three types-metals, non-metals and metalloids.

Metals

We use many metals in our daily life. Our household appliances,
equipments and machines are made of metals. For example, sickle,
axe, knife, khukuri, gates of buildings, grill, shutter, etc are made of
iron. Bowls, plates, spoon, etc are made of steel. Water pot (pitcher),
electric wire, etc are made of copper. The ornaments like chain,
necklace, bracelet, bangle, etc are made of gold. Hence, metals are
very useful in our daily life.
The metals are generally hard solids. They are shiny in appearance
and produce a peculiar metallic sound if struck. The metals conduct
heat

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and electricity from one place to another. Hence, metals are the
elements which are hard, shiny and good conductors of heat and
electricity. Iron, copper, silver, gold, aluminium, etc are some
examples of metals.

Properties of metals

The properties of the metals are called metallic properties. The
metals have the following properties:

1. Physical state and hardness

Generally the metals are hard solids at the room temperature. But,
mercury is a metal which is liquid at the room temperature. The
non-metals may be either solid, liquid or gas at the room temperature.

Activity 12.1
To test the hardness of two solids
Materials required: An iron sheet, a brick, an iron nail, etc.
Procedure

1. Place an iron sheet and a brick on a table.

2. Try to scratch the iron sheet and the brick with the help of the
same iron nail. Which one will be scratched more?

Observation

It is hard to scratch the iron sheet but scratching the brick is
comparatively easy.
Conclusion: The metals are hard solids. The non-metals are not as
hard as metals.

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Conductivity

The property of matter to transfer heat and electricity from one
point to another is called conductivity. Hence, the conductors are
the substances which transfer heat and electricity from one point to
another. Metals are the good conductors of heat and electricity.

Activity 12.2
To identify conductors

Materials required:
An electric circuit, iron nail, thin and short piece of wood, plastic,
coin, steel spoon, thread, long hair, piece of paper, aluminium
wire, ribbon, etc.

Procedure

1. Construct an electric circuit by connecting a bulb with two ends
of a battery with the help of copper wire as shown in the gure.

2. Break the wire at any point and connect the two ends of wires
with the materials mentioned above. Then observe the cases
when the bulb glows.

Observation

When the two ends of wire are connected with the metal pieces such
as iron nail, steel spoon, coin, aluminium wire, etc the bulb glows. It
does not glow in other cases.
Conclusion: The metals are the good conductors of electricity. So,
electricity easily passes through them and the bulb glows.

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Activity 12.3
To test the conductivity of a metal rod and a wooden bar

Materials required: A metal rod and a dry wooden bar.

Procedure

Heat one of the ends of these both rods for same time with a burner.

Observation

You will feel that the iron rod heats up your palm but the wooden bar
does not.

Conclusion:
Iron is a metal and is a conductor of heat. So, it conducts the heat of
re from burner to your hand.

Malleability and ductility

Metals are malleable. It means that metals can be turned into thin
sheets by hammering. Hence, the property of metal due to which it can
be turned into thin sheets on hitting is called malleability. Similarly,
ductility is the property of metal due to which it can be drawn into
thin wire.

But, when the non-metals are hammered, they break down into
pieces. It means that non-metals are brittle. They are not malleable
and ductile.

Strength

The particles or atoms of metals are very closely packed. So, the
metals are stronger than the non-metals. But sodium metal is so soft
that it can be cut into pieces with a knife.

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Activity 12.4
To test the strength of a metal and non-metal

Materials required:
An iron rod and a wooden stick of similar thickness

Procedure

1. Take an iron rod and hold it by its ends. Then try to break it.
2. Similarly, try to break the wooden stick.

Observation:

Which one breaks easily?

You cannot break the iron rod but you can break the wooden stick
easily.

Conclusion:
Iron is a metal and is strong. So, we cannot break it.

Lustre

Metals are lustrous. It means that they have a property of shining.
The shining property of metals is known as lustre. For example, gold
shines in its yellow colour, silver shines in its white colour, etc

Activity 12.5

Observe the lustre of different materials which are made of metals.
You can use knife, ornaments, steel utensils, etc to observe their
lustre.

Metals are sonorous

Metals produce a particular sound when hit by a hard object. A bell
produces sound due to the sonorous property of metal.

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Activity 12.6

Observe the sound produced by different objects while hitting. You
may use steel plate, bowl, bell, spoon, wooden table, desk, brick, etc
to produce sound. What difference would you nd in the sound of
metals and non-metals?

Thus, the properties of metals can be summarized as:
1. Metals are generally hard solids. But mercury is the metal
which is found in liquid state.
2. Metals are the good conductors of heat and electricity.
3. The metals are malleable, i.e. metals can be beaten into thin
sheets.
4. Metals are ductile, i.e. metals can be drawn into wires.
5. Metals are sonorous, i.e. they produce a tinkling sound while
beating.
6. Generally the metals have high melting and boiling points.

Uses of metals

Metals are very important in our daily life. We use metals to make
different appliances, equipments, engines, machines, vehicles,
buildings, etc. The main uses of metals can be summarized in the
following points:

1. Gold, silver and copper are used to make ornaments and medals.
2. They are also used to make coins. So, copper, silver and gold are

also known as coinage metals.
3. Metals are used to make household appliances and tools.
4. They are used to make weapons and other tools.
5. Metals are used to make engines, machines and vehicles.
6. They are also used in the construction of railway tracks, bridges

and buildings.
7. Metals are used to make electrical wires.

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Non-metals

Several non-metals are gases. The non-metals which exist in solid
state are brittle. They are not as hard as metals. Some non-metals
exist in liquid state. The non-metals are not malleable and ductile.
They do not conduct electricity. But graphite is a non-metal that
conducts electricity. Hydrogen, helium, carbon, oxygen, nitrogen,
phosphorus, sulphur, etc are some non-metals.

The common properties of non-metals can be summarized as follows:
1. Non-metals are found in all three states, i.e., solid, liquid and
gas at ordinary temperature.
2. They are brittle, i.e., they are not malleable and ductile.
3. They do not conduct heat and electricity.
4. Non-metals do not have lustre. But iodine and graphite are
the non-metals with lustre.
5. Non-metals are non-sonorous.
6. They usually have low melting and boiling points.

Differences between metals and non-metals

Metals Non- metals

1. Metals are generally solids. 1. Non-metals may be either gas,
Exception: mercury. solid or liquid.

2. Metals are generally hard. 2. Non-metals are generally soft.
Exception: Sodium, Lithium Exception: Diamond, which is
and Potassium which are very the hardest substance known.
soft metals.

3. Metals are malleable and ductile. 3. Non-metals are brittle.

4. Metals are the good conductors 4. Non-metals generally do not
of heat and electricity. conduct heat and electricity.
Exception: Graphite is a good
conductor of electricity.

5. Metals are sonorous. 5. Non-metals are non-sonorous.

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Metalloids

The elements which show the properties common to both metals and
non-metals are called metalloids. The metalloids resemble metals
in some of their properties while they resemble non-metals in other
properties. Silicon, arsenic, germanium, etc are some metalloids.
Some of the common properties of metalloids are as follows:

a. Metalloids are either solid or liquid at ordinary temperature.
b. They are poor conductors of heat and electricity.
c. They are found in powder form.
d. They have metallic lustre.
e. They are not malleable and ductile.

Alloys

When metals are heated strongly, they melt to turn into liquid state.
The liquid states of metals can be mixed with each other to form a
homogeneous mixture. The mixture then becomes
solid on cooling. The homogeneous mixture of two or
more metals or metals and non-metals is known as
alloy. Steel, brass, bronze, etc are some examples of
alloys.

Steel is an alloy of iron and carbon. It is used for numerous purposes.
It is used for making knives, swords, tools, machines, household
appliances, etc. Similarly, brass is an alloy of copper and zinc. Bronze
is an alloy of copper and tin.

Some important metals

Iron

Iron is one of the oldest known and the most essential metals. It is
the second most abundant metal found in the earth’s crust. About
6.2% of the earth’s crust is made up of iron. But iron is not found
in free (pure) state. It is found in the form of compounds such as
haematite, magnetite, iron pyrite, etc. These compounds are called
ores of iron. The pure form of iron is obtained from the ores using
several processes.

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Pure iron is silvery white in colour. It is very hard and is malleable
and ductile. It is a very useful metal. The main uses of iron are:

a. Iron is used to make rods, pipes, nails,
knots and bolts, railway tracks, etc.

b. It is the main part of steel and stainless
steel. Steel is used to make plates, bowls,
glasses, knife, sword and many other
things.

c. Iron forms an important part of red blood cells in our body.
Our blood is red due to the presence of iron.

Copper

Copper is a reddish brown metal
with an attractive metallic lustre. It
occurs in nature in free state as well
as in the form of compounds. The
main compounds that contain copper
in nature are copper pyrite, copper
glance, cuprite, etc. Pure copper is obtained from these compounds
by using several processes.

Copper is used in making utensils, electrical wires and large number
of alloys. It is also used in making coins.

Silver

Silver is a white shinning metal. It occurs in free as well as in
combined state in the earth’s crust. In combined state, it occurs as
silver glance, horn silver, etc.

Silver is used for making ornaments, coins and several silver articles.
It is also used in the production of mirrors.

Gold

Gold is one of the oldest known metals. It occurs
in free state in the hard rocks in the form of ne
gold particles. Since the hard rocks are broken

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into pieces by fast owing rivers and streams, the gold particles are
released from the rocks. Thus, the free state of gold particles is found
in sands of the river banks. People can obtain small amount of gold
by washing the sand of river bank.

Gold is a yellow shining metal. So, it is used in making ornaments,
medals, statues, coins, etc. It is also used in lling teeth. Gold is a
very expensive metal

Main Points to Remember

1. The elements can be categorized into three types-metals,
metalloids and non-metals.

2. Metals are the elements which are hard, shiny and good
conductors of heat and electricity.

3. Non-metals are the elements which are not shiny and are
found in soft solid, gas or liquid state. They do not conduct
electricity.

4. The elements which show the properties common to both
metals and non-metals are called metalloids.

5. A homogeneous mixture of two or more metals or metals
and non-metals is known as alloy.

6. Iron, copper, silver, gold, etc are very useful metals.

Exercise

1. Choose the best alternative in each case:

a. A metal is

i. Malleable ii. Ductile

iii. Sonorous iv. All of these

b. The property of metal due to which it can be drawn into a thin
wire is called

i. Malleability ii. Ductility

iii. Conductivity iv. All of these

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c. A metal that is liquid at the room temperature

i. Sodium ii. Potassium

iii. Mercury iv. Tin

d. Which of the following is a metalloid?

i. Silicon ii. Calcium

iii. Steel iv. Aluminium

e. The alloy of copper and zinc ii. Brass
i. Steel iv. German Silver
iii. Bronze

2. Answer these questions in very short:

a. What are metals?
b. Name the metal which is liquid at ordinary temperature.
c. Name a soft metal which can be cut with a knife.
d. Name a non-metal which conducts electricity.
e. Which is the hardest substance? Is it metal or non-metal?
f. What are coinage metals? Give examples.

3. Dene the following:

a. Metalloid b. Non-metals c. Malleability
f. Alloy
d. Ductility e. Conductivity

4. Write down the uses of: c. Iron
f. Gold
a. Metals b. Non-metals
d. Copper e. Silver

5. Write down differences between:

a. Malleability and ductility

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b. Metals and non-metals
c. Metals and alloys

6. Answer these questions:

a. What are metals? What are the properties of metals?
b. Write down the properties of non-metals.
c. Make separate lists of metals and non-metals that are used

in our daily life.
d. Write down the properties of metalloids.
e. Describe an experiment to show that iron is a good conductor

of heat.

Project Work

1. Collect some objects from your surroundings. Identify their
properties such as conductivity, malleability, brittleness,
lusture, etc. and classify them as metals, non-metals and
metalloids.

2. Make lists of kitchen items which are made up of metals.

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Chapter

13 SOME USEFUL
CHEMICALS

Estimated periods: 5

OBJECTIVES
At the end of the lesson, the students will be able to :
Ü give introduction of some useful chemicals such as common salt,

turmeric, amilo, yeast, etc;
Ü tell the uses of such chemicals.

MIND OPENERS
Ü What will be the taste of your curry if you don’t use common salt?
Ü Why do you use turmeric in your curry?
Ü Where is chook (amilo) obtained from? What is its use? Discuss.

Introduction

We use several compounds in our daily life. These compounds are
regarded as chemicals. For example, we use toothpaste to brush teeth,
shampoo to wash hair, soap to have bath, chilli powder to make curry
hot in taste, etc. In the same way, we use oil to fry vegetables, we use
glycerine to make our skin soft and moist, etc. Here, the substances
like soap, shampoo, toothpaste, chilli powder, glycerine, oil, etc are
made of chemicals.

In addition to these, we use many other chemicals in our daily life. For
example, we use common salt, turmeric, chook (amilo) and chilli in
our curry and pulses. We use baking soda to bake bread and biscuits.
We also use ginger in our curry. The ginger provides hot taste to our
food. It has also a medicinal value. Similarly, there are several other
chemical which are useful for prepare in food or medicinal value. For
example, onion, garlic, etc.

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Common salt

The chemical name of common salt
is sodium chloride. It is obtained by
evaporating the sea water. It is the
most useful substance in our kitchen.
It has a salty taste. Due to this taste,
it is used in pulses (dal), curry and
pickles. It is also used in cooking sh
and meat. Our food becomes tasteless if
we don’t use common salt. The common
salt is also used to preserve sh, meat,
pickles, etc for their future use.

Iodine is another important chemical needed for our body. Iodine is
essential in trace amount and is found in the sea foods. Since Nepal is
far from oceans and seas, it is difcult to obtain sea foods. So, iodine
is mixed with common salt so that everybody consumes it. The salt
mixed with iodine is called iodized salt. The use of iodized salt makes
children mentally active and physically t. It also helps to prevent a
disease called goitre in people.

Turmeric (Besar)

Turmeric is obtained from the underground stem (rhizome) of
turmeric plant. First, the rhizome of turmeric is cleaned and then
cut into slices. The slices are dried in sunshine for several days. Then
the dried slices are ground into ne powder.

Rhizome Turmeric powder TURMERIC
139
Plant Powder
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Book 6

The turmeric powder is yellow in colour. It is used as spices in
vegetables, pulses, pickles, meat and sh while cooking. The
turmeric powder imparts light yellow colour to our foods and makes
them attractive. It also contains different nutrients like proteins,
carbohydrates, minerals, vitamins and bers.
Turmeric also contains some chemicals of medicinal value. So, it is
used in cosmetics and medicines. Hot soup of turmeric and cumin
seeds is used to treat common cold. Lotion of turmeric is used in the
treatment of rashes of skin.

Chook (amilo) or sour juice

Chook (amilo) is a locally produced dark thick syrup with strong sour
taste. It is used in small amount in curry, pickles and chutney to
impart sour taste. This makes our foods delicious. Chemically, the
chook contains citric acid.

Citrus fruits
Chook is obtained from the juice of citrus fruits such as lemon, lime,
sour orange (amilo), sweet lime, shaddock, etc. The juice is obtained
by squeezing the citrus fruits in a squeezer. Thus obtained juice is
ltered and boiled to remove excess of water. When the juice turns
dark and thick, it is ready for use and storage.
Sour juice (chook) not only provides sour taste to our foods but also
it provides us vitamin C.

Baking powder (Khane soda)

Baking powder is the common chemical used in bakeries. It mainly
contains sodium bicarbonate.
The baking powder is used to prepare cakes, breads and biscuits
because it makes them light, soft and enlarges their size.

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The baking soda is also known as edible soda and is used by people
who are suffering from acidity.

Yeast (Marcha)

Yeast is an unicellular, microscopic and non-green plant. It grows
quickly in sugar rich substances. The yeast contains the vitamins B
and E and proteins. The yeast produces an enzyme called zymase.
This enzyme converts the foodstuffs containing sugar into alcohol
and carbon dioxide. Hence, yeast is used to manufacture alcohol,
beer, wine, etc.

The process of conversion of sugars into alcohol by the use of yeast is
called fermentation. Cooked and cooled rice, millet, wheat, potato, etc
can be fermented to alcohol by using yeast.

Yeast can also be used in the production of bread, cake and biscuit.

Main Points to Remember

1. Some of the chemical substances have good taste and other
useful properties.

2. Common salt, baking powder, sour juice, iodine, turmeric,
zymase (an enzyme produced by yeast), etc are some useful
chemicals used in our daily life.

3. The chemical name of common salt is sodium chloride.
4. Turmeric powder is obtained by cleaning, slicing, drying,

and grinding the rhizome of a turmeric plant.
5. Sour juice or chook is a locally produced dark thick syrup

with strong sour taste. Chemically, it contains citric acid.
6. Baking powder is the common chemical used in bakeries.

Exercise

1. Choose the best alternative in each case:

a. The spice that provides hot taste to our food

i. Chilli powder ii. Ginger

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iii. Black pepper iv. All of these

b. The chemical name of common salt is

i. Sodium chloride ii. Citric acid

iii. Calcium chloride iv. Magnesium chloride

c. Which sentence is incorrect about turmeric powder?
i. It is prepared from the leaves of a turmeric powder.
ii. Hot soup of turmeric and cumin seeds is used to treat
common cold.
iii. Turmeric powder is used in cosmetics and medicine.
iv. It contains nutrients such as proteins, carbohydrates,
minerals, vitamins and bres.

d. The main chemical found in baking powder is

i. Sodium chloride ii. Sodium bicarbonate
iii. Sodium carbonate iv. Potassium chloride

e. The use of iodized salt helps to prevent a disease named

i. Marasmus ii. Scurvy

iii. Goitre iv. Beri-beri

2. Answer these questions in very short:

a. What is the chemical name of common salt?
b. Name the part of turmeric plant from which turmeric powder

is made.
c. Name the enzyme produced by yeast.
d. What is the chemical name of baking soda?
e. What is chook?
f. Name the fruits from which sour juice (chook) is obtained.
g. What does yeast contain?

Times' Crucial Science and Environment 142 Book 6

h. Why is baking powder used in bakeries?
i. What does turmeric contain?
j. What is fermentation?

3. Give reasons:

a. We use turmeric powder in our food.
b. We use common salt in our curry and pulses.

4. Answer these questions:

a. Explain the importance of common salt in our food.
b. Why do we need iodine? How do we get it?
c. How is sour juice (chook) obtained from citrus fruits?
d. How is turmeric powder obtained from turmeric plant?
e. What is yeast? How is it useful?

Project Work

What chemicals do you use in your kitchen daily? Enlist them
and mention why they are used.

Times' Crucial Science and Environment 143 Book 6