Modern Concept Science and Technology 9

6. Why is melting of ice a physical change?

Ans: When a solid ice melts into liquid water, no new substance is formed and water can be frozen back into
ice (reversible). So, melting of ice is a physical change.

7. Rusting of iron is a chemical change. Why?

Ans: When moist air comes in contact of iron, rust is formed. Rust has different properties than iron. It cannot be
changed back into iron. Since new substance is formed and change is irreversible, it is a chemical change.

8. Why should chemical equations be balanced?

Ans: Chemicals equations must be balanced in order to satisfy the law of conservation of matter. This law
states " In a closed system matter can neither be created nor be destroyed."

9. Write down the information obtained from a balanced chemical equation.

Ans: Following pieces of information can be obtained from a balanced chemical equation.

1. The names and symbols of reactants and products

2. The total number of atoms or molecules of reactants and products

3. The ratio of molecular weight of reactant and product molecules

4. The type of chemical reaction

10. How can we change magnesium ribbon into magnesium nitrate? Express in chemical equation.

Ans: When a magnesium ribbon is burnt, it gives magnesium oxide.

2Mg + O2 2 Mg O

Magnesium oxide gives magnesium hydroxide in water.

Mg O + H2O Mg (OH)2
When magnesium hydroxide reacts with nitric acid, neutral substances like salt (i.e., magnesium

nitrate) and water are formed.

Mg (OH)2 + 2HNO3 Mg(NO3)2 + 2H2O

STEPS EXERCISE

STEP 1

1. Define:

a) Physical change b) Chemical change
c) Chemical reaction d) Word equation
e) Chemical equation f) Reactants
g) Products h) Unbalanced chemical equation
i) Balanced chemical equation j) Exothermic reaction
k) Endothermic reaction l) Reversible reaction
m) Irreversible reaction n) Catalyst

o) Positive catalyst p) Negative catalyst

STEP 2

2. Give reason:
a) Melting of ice is a physical change.
b) Rusting of iron is a chemical change.

Modern Concept Science - 9 193

c) Chemical equations should be balanced.
d) Formula equation is more informative than a word equation.

3. Differentiate between:
a) Physical change and Chemical change
b) Word equation and Formula equation
c) Reactants and Products
d) Skeleton chemical equation and balanced chemical equation
e) Exothermic reaction and Endothermic reaction

STEP 3

4. Write any three characteristics of physical change.
5. Write down any three examples of physical change.
6. Write any three characteristics of chemical change.
7. Write down any three examples of chemical change.
8. Write any four pieces of information that can be obtained from a balanced chemical

equation.
9. Write down the characteristics of catalyst.

STEP 4

10. Write down the method of writing a balanced chemical equation.

11. Write any four limitations of a balanced chemical equation.

12. Translate the following word equations into balanced formula equations.

a) Hydrogen + Nitrogen Ammonia

b) Hydrogen + Oxygen Water

c) Hydrogen + Chlorine Hydrochloric acid

d) Calcium carbonate Calcium oxide + Carbon dioxide

e) Potassium chlorate Potassium chloride + Oxygen

f) Hydrochloric acid + Sodium hydroxide Sodium chloride + Water

g) Phosphorus + Oxygen Phosphorus pentoxide

h) Iron + Oxygen Iron oxide

i) Ammonium chloride + Calcium hydroxide Calcium chloride + Ammonia + Water

13. Write the balanced chemical equations of the following unbalanced equations.

a) KClO3 KCl + O2 b) H2 + O2 H2O

c) H2O2 H2O + O2 d) Ca(OH)2 + CO2 CaCO3 + H2O

e) H2SO4 + KOH K2SO4 + H2O

f) AgBr Ag + Br2

g) Na2CO3 + CaCl2 CaCO3 + NaCl

h) Na + Cl2 NaCl

194 Chemical Reaction

UNIT Estimated teaching periods Theory Practical
5 3
10
Solubility

Syllabus issued by CDC Solution

 Introduction to solubility
 Unsaturated, saturated solution and supersaturated solution
 Solubility and its simple numericals
 Relation between solubility and temperature
 Solubility curve and its application
 Crystallization process

LEARNING OBJECTIVES

At the end of this unit, students will be able to:
 define unsaturated, saturated and super saturated solution and prepare such solutions.
 define solubility of a substance and explain the relation between solubility and temperature.
 explain crystallization in brief.

Key terms and terminologies of the unit

1. Mixture : A mixture is a mass which is obtained by mixing two or more substances in any
2. Homogeneous mixture : proportion by weight.

The mixture in which mixing components are distributed uniformly and they
cannot be identified by our naked eyes is called homogeneous mixture.

3. Heterogeneous mixture : The mixture in which mixing components are not distributed uniformly and they
can be identified with our naked eyes is called heterogeneous mixture.

4. Solution : A solution is a homogeneous mixture of two or more substances which are mixed
up to a certain limit.
5. Solvent :
6. Solute : A solvent is a substance which dissolves the solute into it to form a solution.

7. Colloid : The component of a solution which is present in relatively less amount and gets
dissolved into a solvent is called solute.
8. Suspension :
The mixture in which the size of component particles of the mixture ranges
between 10–7cm to 10–5cm in diameter is called colloid.

The heterogeneous mixture in which the diameter of mixing particles is 10–5 cm
or large is called suspension.

9. Concentration of the solution : The amount of a solute which is present in a given amount of a solvent is called
concentration of the solution.

10. Unsaturated solution : The type of solution in which further amount of solute can dissolve easily at a
11. Saturated solution : certain temperature is called unsaturated solution.

The solution which cannot dissolve any more amount of solute at a fixed
temperature is called saturated solution.

Modern Concept Science - 9 195

12. Supersaturated solution : The saturated solution prepared at high temperature which throws out excess solute

as a solid on cooling is called supersaturated solution.

13. Solubility : The solubility of a substance at a fixed temperature is the amount of solute (in gram)

required to form a saturated solution in 100 grams of a solvent at that temperature.

14. Solubility curve : The curve obtained by plotting solubility of a substance at different temperatures

along Y-axis and corresponding temperature along X-axis is called a solubility curve.

15. Crystal : A crystal is a solid substance having a fixed geometrical shape bounded by smooth

surfaces and sharp edges.

16. Crystalline solid : The solid substance which is made by repeating crystals is called crystalline solid.

17. Crystallization : The process by which fine crystals are obtained on cooling a hot supersaturated

solution slowly is called crystallization.

18. Amorphous solids : The solid substances which do not have a fixed geometrical shape are called

amorphous solids.

Introduction

In our surroundings, there are many substances which are intermingled with one another.
In atmosphere, different types of gases and dust particles are mixed together. We prepare
'sherbet' by putting sugar into water. Sugar gradually dissolves into the water. Many solutions
of similar types are used in our daily life, such as tea, medicine, drinks, etc. Not only solutions
but also different types of mixtures are also familiar to us. Rice coats in rice, sand in rice, sand
in lime, dust in atmosphere, etc. are some examples of mixture. So, a mixture is a mass which
is obtained by mixing two or more substances in any proportion by weight. In a mixture, the
mixing components do not lose their identity. The components of a mixture are chemically
unreactive and they may be present in solid, liquid or gaseous state. However the mixture of
solid and gas is not found in nature.

Types of Mixture Memory Tips

Depending on the nature, there are two types of mixtures. An alloy is a homogeneous mixture
They are: of two or more metals or metals
and non-metals. For example, brass
i. Homogeneous mixture (Cu+Zn), steel (Fe+C), etc.
ii. Heterogeneous mixture
i. Homogeneous mixture

The mixture in which mixing components are distributed uniformly and Homogeneous mixture
they cannot be identified by our naked eyes is called homogeneous
mixture. In sugar solution, sugar particles are distributed throughout
the water. In brass, metals are mixed uniformly. Sugar solution, salt
solution, soda water, alcohol in water, water in milk, brass, etc. are some
examples of homogeneous mixture.

FACT WITH REASON

Mixture of salt and water is called a homogeneous mixture, why?

Mixture of salt and water is called a homogeneous mixture because dissolved salt particles are
uniformly distributed in the solution. The salt particles are invisible to eyes.

196 Solubility

ii. Heterogeneous mixture Heterogeneous mixture

The mixture in which mixing components are not distributed uniformly
and they can be identified with our naked eyes is called heterogeneous
mixture. Husk in rice, sand in rice, muddy water, dust in air, smoke in air,
etc. are some examples of heterogeneous mixtures.

FACT WITH REASON

Why is muddy water a heterogeneous mixture?
Muddy water is a heterogeneous mixture because mud particles mixed in water are visible to naked eyes.
In muddy water, the mud particles are non-uniformly distributed in water.

Differences between Homogeneous and Heterogeneous mixture

S.N. Homogeneous mixture S.N. Heterogeneous mixture

1. In this mixture, mixing components 1. In this mixture, mixing components are

are distributed uniformly. not distributed uniformly.

2. We cannot identify all the mixing 2. We can identify all the mixing

components. Examples: Salt solution, components. Examples: Muddy water,

brass, etc. stones in rice, etc.

Classification of Mixture

A mixture consists of component particles of different size. On the basis of the size of the
component particles, there are three types of mixture. They are as follows:

i) Solution S.N. Mixture Size of particles
ii) Colloids 1. Solution 10-7 cm or less
iii) Suspension 2. Colloid 10–7 cm to 10–5 cm
3. Suspension 10–5 cm or large

10-7cm or small 10-5cm to 10-7 cm 10-5cm or large

Solution Colloid Suspension

i) Solution

Take a glass of water and add some sugar in it. Stir the mixture till the sugar Solution
disappears. Now, we will get a homogeneous mixture of sugar and water
which is called a solution. So, a solution is a homogeneous mixture of two or
more substances which are mixed up to a certain limit. In a solution, the size of
particles is 10–7 cm or less in diameter. They are so tiny particles that they cannot
be seen with our naked eyes. Solution contains two components, i.e. solute and
solvent. Thus, solution is a homogeneous mixture of solute and solvent.

Solution = Solute + Solvent

Modern Concept Science - 9 197

Solute and Solvent

The component of a solution which is present in relatively large amount is called solvent.

Solvent dissolves the solute to make a solution. Water, alcohol, ether, phenol, petrol, etc. are

the examples of solvent. So, a solvent is a substance which dissolves the solute into it to form

a solution. Similarly, the component of a solution which is present in relatively less amount

and gets dissolved into a solvent is called solute. Sugar, salt, copper sulphate, etc. are the

examples of solute. So, a solute is a substance which dissolves into a solvent.
Memory Tips
Sugar + Water Sugar solution
Water is called a universal solvent
(Solute) (Solvent) (Solution) because most of the organic and inorganic

Differences between Solute and Solvent substances dissolve easily in water.

S.N. Solute S.N. Solvent

1. It is the component of a solution 1. It is the component of a solution which is

which is present relatively less in present relatively more in quantity than

quantity than a solvent. solute.

2. It gets dissolved into a solvent. 2. It dissolves the solute. Examples: Water,

Examples: Sugar, salt, etc. alcohol, petrol, ether, etc.

ii) Colloid

The mixture in which the size of component particles of the mixture ranges between 10–7cm to

10–5cm in diameter is called colloid. When sulphur is dissolved in alcohol and

poured into water, we get a turbid solution. This turbid solution will not settle

even if it is kept for several days. If we filter the turbid solution, filtrate again

gives turbid solution. This type of solution is called colloidal solution or sol. The

particles of a colloid can pass through the filter paper and cannot be seen under a

simple microscope. Milk, blood, gum, etc. are some examples of colloids.

FACT WITH REASON Colloid

Why is blood called a colloid?

Blood is called a colloid because solute particles of blood cannot be separated by filter paper. These solute
particles are also invisible under the simple microscope. Their diameter ranges from 10-7cm to 10-5cm.

iii) Suspension

The heterogeneous mixture in which the diameter of mixing particles is 10–5cm
or large is called suspension. The components of a suspension contain larger
particles so they are visible with naked eyes. The particles of a suspension can be
separated by simple physical methods like filtration, sedimentation, etc. Sand
in water, mud in water, dust particles in air are some examples of suspensions.

FACT WITH REASON Suspension

Dust in air is a suspension. Give reason.

The diameter of dust particles in air is 10–5cm or large. We can see the particles of dust floating in air.
Eventually the dust will settle on the floor and on furniture. So, dust in air is a suspension.

198 Solubility

Concentration of a Solution

The amount of a solute which is present in a given Dilute solution Concentrated
amount of a solvent is called concentration of the of CuSO4 solution of CuSO4
solution. If less amount of a solute is present in more
amount of a solvent, it is called less concentrated or
dilute solution. Similarly, if the amount of the solute
is relatively more, it is called concentrated solution.
Here, concentrated solution is denoted by "conc." and
dilute solution by "dil."

"Dilute" and "concentrated" are relative terms and they do not specify the exact concentration
of the solution. If the amount of a solute in a solution is relatively less, it is called dilute
solution and if the amount of a solute in a solution is relatively more, it is called concentrated
solution. In a dilute solution, there is less solute and less density whereas in a concentrated
solution, there is more solute and more density.

Differences between Dilute solution and Concentrated solution:

S.N. Dilute solution S.N. Concentrated solution

1. It contains relatively less amount of a 1. It contains relatively more amount of

solute in given amount of a solvent. a solute in given amount of a solvent.

2. It has less density. 2. It has more density.

Unsaturated, Saturated and Supersaturated Solution

Take some amount of water and add small amount of copper Memory Tips
sulphate in it. On constant stirring, it gives a solution. In this
solution, more amount of copper sulphate is added and if the An unsaturated solution can be
added extra solute also dissolves, it is known as unsaturated converted into saturated solution
solution. So, the type of solution in which further amount of without adding solute. It is possible
if we cool the unsaturated solution

solute can dissolve easily at a certain temperature is called at low temperature.

unsaturated solution. A saturated solution can be

If we go on adding more amount of copper sulphate to the converted into unsaturated
solution, a condition will appear at which no more copper solution without adding solvent. It
sulphate dissolves at that temperature. This solution is called is possible if we heat the saturated
saturated solution. So, the solution which cannot dissolve any solution up to a high temperature.

more amount of solute at a fixed temperature is called saturated solution.

A saturated solution does not show any change in concentration when it is brought in contact
of a solute. This is because a saturated solution remains in equilibrium state. If we increase
the temperature of the saturated solution, more amount of solute can be dissolved. But when
the solution is cooled down, the extra amount of solute which was dissolved comes out and
sediments at the bottom of the container in the form of crystals. So, the saturated solution
prepared at high temperature which throws out excess solute as a solid on cooling is called
supersaturated solution.

Modern Concept Science - 9 199

17 g CuSO4 20 g of CuSo4 30 °C 24 g of CuSO4
100 g water 100 g water
20 °C 20 °C

A BC

In figure A, the type of solution is unsaturated because 20 g of CuSO4 can be dissolved in 100
g of water at 20°C but the solution has only 17g of CuSO4.

In figure B, the type of solution is saturated as it cannot dissolve any more amount of CuSO4
at 20°C. If we add a crystal of CuSO4 in this solution, it does not dissolve at that temperature
but dissolves only when the temperature is increased.

In figure C, the type of solution is supersaturated. If a crystal of CuSO4 is added to it, the size
of the crystal increases. When the solution is cooled from 30°C to 20°C, it throws 4 gram, i.e.
(24g–20g) of CuSO4 as solid in the solution.

Differences between Saturated solution and Unsaturated solution:

S.N. Saturated solution S.N. Unsaturated solution

1. In this solution, no more solute can 1. In this solution, more amount of solute can

dissolve at the given temperature. dissolve easily at the given temperature.

2. It has more saturation and more density. 2. It has less saturation and less density.

Differences between Saturated solution and Supersaturated solution:

S.N. Saturated solution S.N. Supersaturated solution

1. In this solution, no more solute can 1. It is the saturated solution prepared at

dissolve at the given temperature. high temperature.

2. Its concentration does not change 2. Its concentration decreases when it

when it comes in contact of a solute. comes in contact of a solute.

Importance of Solution

1. Plants absorb food and minerals from the soil in the form of a solution.
2. Aquatic organisms take dissolved oxygen from the water in the form of a solution.
3. Most of the medicines are prepared in the form of a solution.
4. The digested food is distributed throughout the body in the form of a solution.
5. Many chemical reactions occur in the form of a solution.

ACTIVITY 1

Objective : To prepare unsaturated, saturated and supersaturated solution
Materials required : Copper sulphate, water, beaker, Bunsen burner, tripod stand, glass
rod, matchbox

200 Solubility

Procedure
i. Take 50 ml of water in a beaker. Add some amount of copper sulphate into it and stir it

with a glass rod.
ii. Go on adding the extra amount of copper sulphate and stir the solution till the added

solute stops to dissolve.
iii. Increase the temperature of the solution and add more amount of copper sulphate.
Observation : Initially solute dissolves easily but after some time no more solute can dissolve.
However, after increasing temperature, more amount of solute gets dissolved.
Conclusion : The first condition is called unsaturated solution, second condition is called
saturated solution and the last condition is called supersaturated solution.

Glass rod CuSO4 Glass rod

Beaker

Beaker

CuSO4

Stand Burner
Burner

Solubility

The solubility of a substance at a fixed temperature is the amount of solute (in gram) required
to form a saturated solution in 100 grams of a solvent at that temperature. Different substances
have different solubility because they have different physical and chemical properties. The
solubility of a substance can be calculated by using the given formula.

Weight of solute (in gram)
Solubility = Weight of solvent (in gram) × 100

For example, the solubility of copper sulphate is 25 at Memory Tips
30°C. It means that 25 grams of copper sulphate dissolves
in 100 grams of water at 30°C to form a saturated solution. Solubility does not have any unit
Solubility has no unit as it is the percentage ratio of two because it is a pure ratio of two
similar physical quantities. same physical quantities (i.e. mass).

The solubility of some common substances at 20°C and 30°C temperature is given below:

S. No. Substances (Solutes) Solubility at 20°C Solubility at 30°C
1. Sodium chloride 35.7 37
2. Sodium nitrate 88 95
3. Copper sulphate 20 24
4. Ammonium chloride 37 41
5. Potassium nitrate 27 37
6. Magnesium chloride 32 34

Modern Concept Science - 9 201

From the given table above, it becomes clear that different solutes have different solubility at a
fixed temperature and the same solute has different solubility at different temperatures. It also
shows that the solubility of a solute increases with increase in temperature and vice-versa.

Worked out Numerical 1

Find out the solubility of a salt when 44g of it is dissolved in 50 g of water at 20°C temperature.
Solution:
Given, At 20°C,

Weight of salt (solute) = 44 g

Weight of water (solvent) = 50 g

Solubility = ?

Wt. of solute (in gram) 44g
Solubility = Wt. of solvent (in gram) × 100 = 50g × 100 = 88

Therefore, the solubility of the salt is 88 at 20°C.
Worked out Numerical 2

The solubility of copper sulphate at 30°C is 24. What amount of water is required to make
a saturated solution of 0.5 kg of copper sulphate?

Solution:

Given, At 30°C,

Solubility = 24

Weight of solute = 0.5 kg = 500 g [∵ 1 kg = 1000 g]

Weight of solvent = ?

Wt. of solute (in gram)
Now, solubility = Wt. of solvent (in gram) × 100

500
or, 24 = Wt. of solvent (in gram) × 100

500
or, Solvent = 24 × 100 = 2083.33 g
Therefore, the weight of solvent (water) is 2083.33 g.
Worked out Numerical 3

If 20 g saturated solution contains 8 g of a solute at 25°C, calculate the solubility of the
solute.

Solution: Given,

At 25° C

Weight of saturated solution = 20 g

Weight of solute = 8 g

Weight of solvent = Weight of solution – Weight of solute = 20g – 8g = 12g

Solubility = ?

202 Solubility

We know,

Wt. of solute (in gram) 8
Solubility = Wt. of solvent (in gram) × 100 = 12 × 100 = 66.66

Therefore, the solubility of the solute is 66.66 at 25°C.

Worked out Numerical 4

If 20 g saturated solution at 80°C is cooled down to 30°C, how many grams of solute will be
crystallized out. The solubility of the solute at 80°C is 100 and at 30°C is 25.

Solution: Given,

At higher temperature, i.e. 80°C

Let, Weight of solute = x g

Weight of solution = 20 g

∴ Weight of solvent = (20 – x) g

Solubility = 100

Wt. of solute (in gram)
Now, solubility = Wt. of solvent (in gram) × 100

x
or, 100 = 20 – x × 100

or, x = 10 g

So, Weight of solvent = Weight of solution – Weight of solute = 20 – 10 = 10 g

At lower temperature, i.e. 30°C

Let, Weight of solute = y g

Weight of solvent = 10 g

Solubility = 25

Now,
Wt. of solute (in gram)

Solubility = Wt. of solvent (in gram) × 100

y
or, 25 = 10 × 100

or, y = 2.5 g

Therefore, the amount of solute that crystallizes on cooling = x – y = 10 – 2.5 = 7.5 g

∴ When the given solution is cooled from 80°C to 30°C, 7.5 gm crystals are obtained.

Factors Affecting Solubility

Different factors affect the solubility of a solute. Some of them are described below:

i. Temperature

Temperature is one of the major factors that affect the solubility of a solute. When temperature
is increased, solubility of a substance also increases and vice-versa. When the temperature
of solution is increased, the kinetic energy of solute and solvent molecules also increases.
As a result, intermolecular space among the molecules of the solvent increases. Hence, more
amount of solute gets dissolved at high temperature.

Modern Concept Science - 9 203

Similarly, when temperature is decreased, kinetic energy of the solute and solvent molecules
is also decreased. As a result, spaces of the solvent molecules decrease. Hence, solution throws
out the excess solute in the form of crystals.

FACT WITH REASON

When a saturated solution is cooled it changes into supersaturated solution. Give reason.
When a saturated solution is cooled it changes into super-saturated solution because it starts to throw out
the solute as a crystal or sediment.
When a saturated solution is heated it changes into unsaturated solution. Give reason.
When a saturated solution is heated, the intermolecular space among the molecules of the solvent increas-
es. Hence, more amount of solute gets dissolved at high temperature. So, when a saturated solution is heat-
ed it changes into an unsaturated solution.
Temperature is always mentioned along with the solubility of a substance, why?
Temperature is always mentioned along with the solubility of a substance because solubility of a substance
is directly proportional to the temperature of the solvent. If temperature increases solubility also increases.

ii. Size of particles

Small sized solute particles dissolve more rapidly than the lump. This is because small size
of solute particles increases the total surface area and decreases the surface area of individual
particle. Hence, tiny particles of a solute can enter into the small spaces.

Solubility Curve SolubilityY
Potassium nitrate
Solubility of most of the substances increases with 120 Magnesium chloride
increase in temperature and decreases with decrease in 110 X
temperature. The best way to show this relation is by 100 Calcium sulphate
using simple graph line. So, the curve obtained by plotting
solubility of a substance at different temperatures along 90 4 6 8 10 12 14 16 18 20
Y-axis and corresponding temperature along X-axis 80 Temperature in °C
is called a solubility curve. Different substances have 70
different solubility curve. Potassium nitrate, potassium 60 Solubility curve
chloride, sodium chloride, etc. show the continuous 50
solubility curve without break. In these substances, 40
solubility increases with increase in temperature. 30
20
10

02

Sodium sulphate is an example of a solute whose solubility increases with increase in
temperature up to 32.4°C. After this temperature, solubility decreases with increase in
temperature. So, this type of curve line is called discontinuous curve with break.

Information obtained from solubility curves

1. Solubility curve can be used to find out the solubility of a substance at given temperature.

2. Solubility curve shows the variation of solubility with temperature.

3. Solubility curve can be used to compare the solubility of different substances at different
temperatures.

4. The amount of a solute that crystallized out after cooling the solution can be calculated.

5. The substances which undergo crystallization first can be predicted.

204 Solubility

Crystalline Solids

A crystal is a solid substance having a fixed geometrical shape bounded by smooth surfaces
and sharp edges. Crystals are arranged in a specific three dimensional pattern. Different types
of solids have crystals of different shape and size. The solid substance which is made by
repeating crystals is called crystalline solid. It has a fixed geometrical shape and fixed melting
point and boiling point. Sodium chloride, copper sulphate, sugar, etc. are some examples of
crystalline solids.
Characteristics of crystals

1. They have a definite geometrical shape.
2. They have sharp melting point.
3. They are held together by their sharp edges.
4. They are present in pure form.

Crystallization

The process by which fine crystals are obtained on cooling a hot supersaturated solution
slowly is called crystallization. When a saturated solution at higher temperature is cooled
down slowly, it throws the extra solute in the form of crystals and sediments at the bottom of
the container. These crystals are observed under a microscope to find out the shape.

FACT WITH REASON

When a supersaturated solution of copper sulphate is cooled, bluish solid is seen, why?
When a supersaturated solution of copper sulphate is cooled the intermolecular space in the solvent de-
creases. The crystals of copper sulphate are thrown out from the solution due to fall in temperature. Such
crystals are seen as a bluish solid in the solvent.

ACTIVITY 2

Objective : To get crystals of copper sulphate
Materials required : Copper sulphate, water, glass rod, evaporating
beaker, tripod stand, Bunsen burner
Procedure
Prepare the saturated solution of copper sulphate at higher
temperature by keeping solid copper sulphate in the solution with
constant stirring. Now, the solution is allowed to cool down at room
temperature slowly.
Observation : We will get residue (crystals) at the bottom of evaporating dish. Now, these
crystals are observed under a microscope.
Conclusion : Fine crystals of copper sulphate are obtained.

Amorphous Solids

The solid substances which do not have a fixed geometrical shape are called amorphous
solids. Glass, rubber, plastic, etc. are some examples of amorphous solids. These solids do not
melt on heating but become soft.

Modern Concept Science - 9 205

ANSWER WRITING SKILL

1. What is the size of solute particles in a solution?

Ans: The size of solute particles in a solution is 10-7cm or less in diameter.

2. What is solution? Give any two examples.

Ans: The homogeneous mixture of solute and solvent is called solution. In solution, the size of solute particles
is 10-7 cm or less. Example, copper sulphate solution, sugar solution, etc.

3. Define dilute and concentrated solution.

Ans: A solution which has comparatively less amount solute than another for the same volume of solvent is
called dilute solution.

A solution which has comparatively more amount of solute than another solution for the same volume
of solvent is called concentrated solution.

4. What is a supersaturated solution?

Ans: A saturated solution at higher temperature is called supersaturated solution. It throws solute if cooled.

5. Define crystalline solid with an example.

Ans: A solid which is made by repeating crystals is called crystalline solid. Example, alum

6. Mixture of salt and water is called a homogeneous mixture, why?

Ans: Mixture of salt and water is called a homogeneous mixture because salt particles are uniformly
distributed throughout the solution. In the solution, the salt particles are invisible to eyes.

7. What does it mean by solubility of sodium chloride at 20˚C is 36?

Ans: Solubility of sodium chloride at 20˚C is 36. It means 36 gram of sodium chloride can be dissolved in 100
gram of water at 20˚C to make a saturated solution.

8. What are the major differences between solute and solvent?

Ans: Differences between solute and solvent are:

S.N. Solute S.N. Solvent

1. Solute is a component of solution which 1. Solvent is a component of solution which
gets dissolved in solvent. can dissolve other solutes in it.

2. Solutes are relatively less in amount than 2. Solvents are relatively more in amount
solvent. Example: sugar than solute. Example: Water

9. Why is it possible to dissolve more amount of solute in a solution when a saturated solution is heated?

Ans: It is possible to dissolve more amount of solute in a solution when a saturated solution is heated. This
is because when saturated solution is heated the solvent molecules expand in a large volume creating
more intermolecular space. Hence, more solute molecules can be dissolved easily.

10. Temperature is always mentioned along with the solubility of a substance, why?

Ans: Temperature is always mentioned along with the solubility of a substance because solubility of a
substance is directly proportional to the temperature of the solvent. If temperature increases solubility
also increases.

206 Solubility

11. Suppose you are given a sugar solution in two different test tubes. With the help of sugar crystals, how
can you identify the solution is saturated or unsaturated?

Ans: If I get sugar solution in two different test tubes and some sugar crystals, then I will keep sugar crystals
into the both solutions to check whether they are saturated or unsaturated. The solution which dissolves
sugar crystals is an unsaturated solution and the solution which cannot dissolve sugar crystal is a
saturated solution.

STEPS EXERCISE b) Heterogeneous mixture
d) Solvent
STEP 1 f) Colloid
h) Concentration of the solution
1. Define the following terms. j) Saturated solution
l) Solubility
a) Homogeneous mixture n) Crystal
c) Solution p) Crystallization
e) Solute
g) Suspension
i) Unsaturated solution
k) Supersaturated solution
m) Solubility curve
o) Crystalline solid
q) Amorphous solids

2. Write any two examples of colloid and suspension.

3. Write down the formula to calculate the solubility of a substance.

4. Give any two examples each of crystalline and amorphous solids.

STEP 2

5. W hat does it mean by the statement that the solubility of sodium nitrate at 20°C is 88?

6. Differentiate between:
a) Homogeneous mixture and Heterogeneous mixture
b) Solute and Solvent
c) Colloid and Suspension
d) Dilute solution and Concentrated solution
e) Unsaturated solution and Saturated solution
f) Crystalline solids and Amorphous solids

7. Give reason:
a) The mixture of sugar and water is called a homogeneous mixture.
b) The mixture of sand and salt is called a heterogenous mixture.
c) More amount of solute can be dissolved by heating a saturated solution.
d) Solute separates as a solid while cooling a saturated solution.

Modern Concept Science - 9 207

e) Temperature is mentioned along with the solubility of a substance.
f) The solubility of a solute increases on increasing the temperature of a solvent.

STEP 3

8. Describe the importance of solution in brief.

9. What is the effect of temperature on solubility of a substance? Explain.

10. Write any three pieces of information that can be obtained from solubility curves.

11. Write any three characteristics of crystals.

12. What is meant by crystallization? How are crystals prepared?

13. Numerical Problems:

a) A saturated solution is formed when 50 gram of a salt dissolves in 20 gram of water at

60°C. Calculate the solubility of the salt at the given temperature. [Ans: 250]

b) At 50°C, 2 gram of a salt remains as a residue after drying 7 gram of a saturated

solution. Calculate the solubility of the salt at that temperature. [Ans:40]

c) At 55°C, how much solute is required to make a saturated solution in 250 g of a

solvent? The solubility of a salt at that temperature is 50. [Ans: 125 g]

d) Calculate the amount of solvent required to make a saturated solution of a solute
of 80 gram at 60°C. The solubility of the solute at that temperature is 40. [Ans: 200g]

e) Calculate the amount of solute that separates as a solid when 30 gram of a

saturated solution prepared at 50°C is cooled to 30°C. The solubility of the given

solute is 35 at 50°C and 21 at 30°C . [Ans : 3.11 g]

STEP 4

14. Plot solubility curves on the basis of given data and answer the following questions:

Temp. (°C) 0 10 20 30 40 50
Solubility of NaCl 25 30 36 37 39 40
Solubility of NH4 Cl 28 33 37 41 46 51

a) What is the solubility of NaCl and NH4Cl at 35°C ?
b) What happens when a saturated solution of NaCl is cooled from 40°C to 25°C?

c) Find out the solubility of NH4Cl at 45°C and 15°C.
d) What is the relation between increase in temperature and solubility?

208 Solubility

UNIT Estimated teaching periods Theory Practical
5 3
11
Some Gases

Syllabus issued by CDC Henry Cavendish

 Hydrogen gas (laboratory preparation, properties and uses).
 Oxygen gas (laboratory preparation, properties and uses).
 Nitrogen gas (laboratory preparation, properties and uses).

LEARNING OBJECTIVES

At the end of this unit, students will be able to:
 prepare hydrogen, oxygen and nitrogen gases in laboratory.
 explain physical properties, chemical properties and uses of hydrogen, oxygen and nitrogen gases.

Key terms and terminologies of the unit

1. Laboratory preparation of hydrogen : In the laboratory hydrogen gas can be prepared
by the reaction of zinc granules with dilute
hydrochloric acid or dilute sulphuric acid.

2. Chemicals required for hydrogen preparation : Dilute hydrochloric acid (HCl) or dilute
3. Laboratory preparation of oxygen : sulphuric acid (H2SO4) and Zinc granules (Zn).
When 3:1 ratio of potassium chlorate and
manganese dioxide is heated at about 250
°C, we get oxygen gas.

4. Chemicals required for oxygen preparation by using heat: Potassium chlorate (KClO3) and Manganese

dioxide (MnO2)

5. Chemicals required for oxygen preparation without using heat: Hydrogen peroxide (H2O2) and Manganese
dioxide (MnO2)

6. Laboratory preparation of nitrogen : In laboratory, nitrogen gas is prepared by

heating a mixture of ammonium chloride and

sodium nitrite in solution state.

7. Chemicals required for nitrogen preparation: Ammonium chloride (NH4Cl) and Sodium
nitrite (NaNO2)

A. HYDROGEN GAS

Introduction

The earth is surrounded by a thick layer of air which is called atmosphere. The air consists
of various gases like nitrogen, oxygen, carbon dioxide, neon, argon, water vapour, etc. About
99% volume of the air is occupied by nitrogen and oxygen. The different gases present in air
with their percentage volume are given below:

Modern Concept Science - 9 209

S.N. Gases in air Volume (%)

1. Nitrogen (N2) 78.08
2. Oxygen (O2) 20.95
3. Carbon dioxide (CO2) 0.0360
4. Argon (Ar) 0.93

5. Neon (Ne) 0.002

6. Hydrogen (H2) 0.00005
7. Ozone (O3) 0.000004
8. Other gases (Ne, He, CH4, N2O) 0.003945

Many elements exist in gaseous state. Some of them are hydrogen, helium, nitrogen, oxygen,
neon, chlorine, argon, krypton, etc. Gases are very useful for human beings as well as other
organisms. Hydrogen gas is used to fill balloons and prepare vegetable ghee. Oxygen gas is
used by living organisms for breathing. Nitrogen gas is used for making chemical fertilizers.
Carbon dioxide is used by green plants for photosynthesis. It is also used in soft drinks like
coca-cola, beer, soda water, etc.

In this unit, we will study the occurrence, laboratory preparation, industrial preparation,
properties and uses of hydrogen, oxygen and nitrogen.

Symbol H 1p+ 1 p +
Atomic number 1 Molecular structure of hydrogen gas
Atomic mass 1
Valency 1
Molecular formula H2
Molecular weight 2
Electronic configuration 1s1

Discovery

Henry Cavendish, a British scientist, discovered hydrogen gas in 1766 AD and named it
"inflammable gas". Later in 1783 AD, Antony Lavoisier proposed the name hydrogen (Greek
word, hydro-water, genas – produce) because it produces water on burning with oxygen.

Occurrence

Hydrogen is the lightest, simplest and reactive element. Thus, it does not occur in free state in
nature. In combined state, it is present in different compounds like water, acids, hydrocarbons,
carbohydrates, etc. Large amount of hydrogen is present in the sun and its trace is present in
volcanic gases. The chief source of hydrogen on the earth is water.

General Methods of Preparing Hydrogen Gas

Hydrogen gas can be prepared by either of the following methods.

210 Some Gases

i. From water

Hydrogen gas can be prepared by the electrolysis of water.

2H2O Electricity 2H2 + O2 Memory Tips

Hydrogen gas can also be prepared by the reaction A small chunk of the pure sodium
of active metals like sodium, potassium with water at metal or potassium metal dropped
ordinary temperature. into water causes a big flash and
bang.
2Na + 2H2O 2NaOH + H2

2K + 2H2O 2KOH + H2
ii. From acids
Memory Tips

Electropositive metals like iron, zinc, magnesium, etc. During apparatus setup for the
react with acids to give hydrogen gas. laboratory preparation of gases,
the end of thistle funnel must be
Zn + dil. H2SO4 ZnSO4 + H2

Mg + dil. 2HCl MgCl2 + H2 dipped inside the liquid so that
iii. From alkalis the gas produced will not be
leaked from the thistle funnel. But

Metals react with alkalis to give hydrogen gas. delivery tube must not be dipped
in the solution so that the gas
Zn + 2NaOH Na2ZnO2 + H2 produced gets collected in the
gas jar through delivery tube.
(Sodium zincate)

2Al + 2NaOH + 2H2O 2NaAlO2 + 3H2

(Sodium aluminate)

Laboratory Preparation of Hydrogen Gas

Dilute H2SO4 Delivery tube
Thistle funnel

Cork Hydrogen gas
Gas jar

Woulfe's bottle Beehive shelf
Granulated zinc
Water trough
Water

Laboratory preparation of hydrogen gas (H2)

Principle

In laboratory, hydrogen gas can be prepared by the reaction of zinc granules with dilute
hydrochloric acid or dilute sulphuric acid.

Zinc + dil. Hydrochloric acid Zinc chloride + Hydrogen

Modern Concept Science - 9 211

Zn + dil. 2HCl ZnCl2 + H2
Zinc + dil. Sulphuric acid
Zinc sulphate + Hydrogen

Zn + dil. H2SO4 ZnSO4 + H2
Apparatus required

i. Woulfe's bottle ii. Thistle funnel iii. Gas jar

iv. Delivery tube v. Water trough vi. Beehive shelf

vii. Cork

Chemicals required

i. Dilute hydrochloric acid (HCl) or dilute sulphuric acid (H2SO4)

ii. Zinc granules (Zn) Memory Tips
Procedure

i. Keep some granules of zinc in the Woulfe's bottle and • The experiment should be
arrange the apparatus as shown in the figure.
performed away from the fire;

ii. Pour dilute hydrochloric acid or dilute sulphuric acid otherwise hydrogen itself burns
and may cause explosion.
through the thistle funnel.
• If the reaction occurs slowly, we
When zinc reacts with dilute acid, it gives off hydrogen • should use little amount of copper
gas. This gas passes through delivery tube. The gas is sulphate to accelerate the reaction.
collected in the gas jar by downward displacement of Impurities present in the zinc also
water. play a role of positive catalyst in

Precautions the reaction.

i. The apparatus should be made airtight.

ii. We should take granulated impure zinc.

iii. We should not use concentrated sulphuric acid.

iv. The lower end of the thistle funnel must be dipped in the acid solution.

v. The experiment must be conducted away from the fire.

FACT WITH REASON

We should use impure granulated zinc to prepare hydrogen gas in the laboratory, why?

We should use impure granulated zinc to increase the rate of chemical reaction because pure zinc reacts
very slowly with dilute acid.

Why we cannot use conc. sulphuric acid instead of dil. sulphuric acid to prepare hydrogen in the
laboratory.

Concentrated sulphuric acid produces sulphur dioxide gas (SO2) in place of hydrogen gas. So, we should use
dilute sulphuric acid to prepare hydrogen gas in the laboratory.

Hydrogen gas is collected by downward displacement of water, why?

Hydrogen is the lightest known gas. It cannot be collected in an open gas jar. Also hydrogen is slightly
soluble in water. So, it is collected by downward displacement of water.

212 Some Gases

Test of Hydrogen Gas

When a burning match stick is introduced into the gas jar containing the gas produced, the gas
burns with pale-blue flame and the matchstick gets extinguished with a pop sound. It proves
that the gas is hydrogen.

Manufacture of Hydrogen Gas

For commercial purpose, hydrogen gas is prepared in the following two ways.
i. From methane – steam reaction

When a mixture of methane gas and water vapour is heated strongly at about 1200°C

temperature and 30 atm. pressure with nickel as Memory Tips

catalyst, we get hydrogen gas. Catalyst is a chemical substance

CH4 + H2O 1200ºC/30 atm. CO + 3H2 which either increases or decreases
Ni the rate of chemical reaction, itself
remaining chemically unchanged.
ii. By the electrolysis of water

Hydrogen gas can also be manufactured

by passing electricity in the acidified water.

When we supply current, water molecules

dissociate into opposite ions and move

towards respective electrodes (H+ at cathode

and OH– at anode).

Hydrogen ions have positive charge. So, they Electrolysis of water
move towards the cathode and change into
hydrogen gas. Similarly, hydroxyl ions have
negative charge. So, they move towards the
anode and change into oxygen gas.

2H2O Electricity H2 + O2
+ H2SO4

Physical Properties of Hydrogen Gas

i. It is a colourless, odourless and tasteless gas.

ii. It is the lightest gas.

iii. It is neutral to indicators.

iv. It is slightly soluble in water.

v. It becomes liquid at –253°C and becomes solid at –259°C.

FACT WITH REASON

Why do people use hydrogen gas to fill in air balloons?

People use hydrogen gas to fill in air balloons because hydrogen gas is the lightest among all the gases and
flies up in the air.

Modern Concept Science - 9 213

Chemical Properties of Hydrogen Gas
i. Reaction with air

Hydrogen gas burns with air or oxygen and forms water.

2H2 + O2 ∆ 2H2O

ii. Reaction with metals

Metals like sodium, potassium, etc. react with hydrogen gas to give corresponding

metallic hydrides.

2Na + H2 300º C 2NaH (Sodium hydride)

Ca + H2 300º C CaH2 (Calcium hydride)

iii. Reaction with halogens

Halogens like fluorine, chlorine, bromine react with hydrogen to give corresponding

acids.

H2 + F2 In dark 2HF (Hydrofluoric acid)

H2 + Cl2 Light 2HCl (Hydrochloric acid)

H2 + Br2 400º C 2HBr (Hydrobromic acid)

H2 + I2 440º C 2HI (Hydrogen iodide)

iv. Reaction with metallic oxides

Hydrogen reduces the metallic oxides Hydrogen gas Lead oxide Excess hydrogen
into free metals when it is passed through (PbO) and water vapour

heated metallic oxides. This property of

hydrogen is called reducing property of Burner
Stand
hydrogen.

CuO + H2 ∆ Cu + H2O

PbO + H2 ∆ Pb + H2O

Fe3O4 + 4H2 ∆ 3Fe + 4H2O

ZnO + H2 ∆ Zn + H2O

v. Reaction with nitrogen

Hydrogen reacts with nitrogen at 500oC temperature and 200 atm. pressure in the

presence of iron catalyst and molybdenum promoter to give ammonia gas.

3H2 + N2 500ºC, 200 atm. 2NH3

Fe/Mo

214 Some Gases

vi. Reaction with unsaturated hydrocarbons C to C double C to C single
bond bond

unsaturated saturated

Hydrogen combines with unsaturated hydrocarbons Ni

to give saturated hydrocarbons. Hydrogen gas Catalyst

C2H4 Ni C2H6 Ethene Colourless - Ethane

(Ethene) (Ethane) Hydrogenation of ethene

Hydrogenetaion Memory Tips

When hydrogen gas is passed into vegetable oil Vegetable oil is an unsaturated fat.
at about 200oC and 8-10 atmospheric pressure in Hydrogenation converts vegetable

the presence of nickel it forms vegetable ghee. This oil into vanaspati ghee which is a

process is called hydrogenation. saturated fat.

H2 + vegetable oil 8 – 10 atm. vegetable ghee
Ni / 200ºC

Uses of Hydrogen Gas

i. In the past, hydrogen gas was used to fill the balloons and ships because it is
the lightest gas.

ii. It is used in the manufacturing of vegetable ghee by the process of hydrogenation.

iii. It is used as a fuel in rockets.

iv. It is used in the manufacturing of ammonia gas and chemical fertilizers.

v. It is used as a reducing agent.

vi. It is used for making oxyhydrogen flame for cutting and welding of metals.

FACT WITH REASON

Hydrogen and oxygen gases are used in welding and cutting of metals, why?
Oxy-hydrogen flame is produced when a mixture of hydrogen and oxygen is burned. This flame produces
very high temperature of about 3000˚C. So, it is used in welding and cutting of metals.

B. OXYGEN GAS O 8p+ 8p+
8 8no 8n°
Symbol 16
Atomic number 2 Molecular structure of oxygen gas
Atomic mass O2
Valency 32
Molecular formula 1s2, 2s2, 2p4
Molecular weight
Electronic configuration

Modern Concept Science - 9 215

Discovery

Oxygen was discovered by a Swedish chemist Scheele in 1773 AD and named as fire air or
vital air. An English scientist Joseph Priestly called it perfect gas or very active gas. In 1776
AD, French scientist Antony Lavoisier gave the name "oxygen".

Occurrence

Oxygen occurs free as well as in combined state in nature. It constitutes about 48% of the
earth's crust and about 21% of the atmosphere. In combined state, it is present as a constituent
of different compounds like acid, base, salt, fat, carbohydrate, protein, sand, etc. About 72% of
the human body is occupied by oxygen. More than 49% of the materials found on the earth's
surface are the compounds of oxygen.

General Methods for the Preparation of Oxygen Gas
i. From metallic oxides

Metallic oxides like mercuric oxide, lead oxide, etc. give oxygen gas after heating.

2HgO ∆ 2Hg + O2

2PbO ∆ 2Pb + O2

ii. From metal peroxides

Oxygen gas can be prepared when metal peroxides like sodium peroxide, potassium
peroxide, etc. are treated with water.

2Na2O2 + 2H2O 4 NaOH + O2

2K2O2 + 2H2O 4 KOH + O2

Laboratory Preparation of Oxygen Gas

There are two methods of preparing oxygen gas in the laboratory. They are:

a. By using heat

b. Without using heat
a. By using heat

Hard glass test tube Cork Oxygen gas
Potassium chlorate Delivery tube Gas jar

+
Manganese dioxide

Stand Water trough
Beehive shelf
Bunsen burner

Laboratory preparation of oxygen gas (O2) by using heat

216 Some Gases

Principle

When 3:1 ratio of potassium chlorate and manganese dioxide is heated at about 250 °C,

we get oxygen gas.

Potassium chlorate 250ºC Potassium chloride + Oxygen
MnO2
2KClO3 250ºC
MnO2 2KCl + O2

Apparatus required

i. Hard glass test tube ii. Delivery tube

iii. Water trough iv. Beehive shelf

v. Gas jar vi. Bunsen burner

vii. Cork viii. Stand

Chemicals required

i. Potassium chlorate (KClO3)
ii. Manganese dioxide (MnO2)
Procedure

i. The 3:1 ratio of potassium chlorate and manganese dioxide is kept in the hard
glass test tube and the apparatus is set as shown in the figure.

ii. Heat is supplied by Bunsen burner.

iii. When potassium chlorate is decomposed, it gives off oxygen gas.

iv. The oxygen gas produced in the hard glass test tube is collected in the gas jar by
downward displacement of water.

Precautions

i. We should take pure manganese dioxide (MnO2).
ii. The hard glass test tube should be made inclined.

iii. Heat should be supplied constantly.

iv. The apparatus should be made airtight.
b. Without using heat

Hydrogen peroxide

Stopper Delivery tube

Cork Oxygen gas
Conical flask Gas jar

Mixture of H2O2 + MnO2 Beehive shelf Water
Water trough

Laboratory preparation of oxygen without using heat

Modern Concept Science - 9 217

Principle Memory Tips
Oxygen gas can be prepared in the laboratory by the

decomposition of hydrogen peroxide in the presence • Oxygen is not inflammable

of manganese dioxide. but a very good supporter of

Hydrogen peroxide MnO2 water + oxygen combustion.
• Nascent oxygen is an atomic form
H2O2 MnO2 H2O + O2
of oxygen which is produced
Apparatus required during chemical reaction. It is

i. Conical flask ii. Thistle funnel more reactive and it has more

iii. Delivery tube iv. Gas jar internal energy.
v. Beehive shelf vi. Water trough • Manganese dioxide (MnO2) is a
vii. Cork viii. Stopper
positive catalyst which increases
the rate of chemical reaction.

Chemicals required

i. Hydrogen peroxide (H2O2)
ii. Manganese dioxide (MnO2)
Procedure

i. Keep some manganese dioxide in the conical flask and arrange the apparatus as
shown in the figure.

ii. Pour hydrogen peroxide drop by drop with the help of the stopper.

iii. When hydrogen peroxide decomposes in the presence of manganese dioxide, it
gives off oxygen gas.

iv. Oxygen gas produced in the conical flask is passed through the delivery tube and
it is collected in the gas jar by downward displacement of water.

FACT WITH REASON

Oxygen gas is collected by downward displacement of water, why?

Oxygen is a light gas. Also it is less soluble in water. So, oxygen is collected by downward displacement of
water.

Test of Oxygen Gas

i. When a burning match stick is brought near the mouth of the gas jar, the flame becomes
brighter indicating that the gas jar is filled with oxygen gas.

ii. When a burning magnesium ribbon is kept inside the gas jar, it burns and gives white
ash of magnesium oxide (MgO). It also proves that the gas is oxygen.

FACT WITH REASON

Why a burning lighter glows brighter when introduced in a gas jar with oxygen gas?
Burning lighter glows brighter when introduced in a gas jar with oxygen gas because oxygen gas helps in
combustion.

218 Some Gases

ACTIVITY 1

• Take some potassium permanganate in a hard glass test tube.

• Heat the test tube gently by using a Bunsen burner. A gas is produced during this process.

• Collect the gas in a test tube.

• Identify the gas produced by this process.

2KMnO4 ∆ K2MnO4 + MnO2 + O2

Manufacture of Oxygen

For commercial purpose, oxygen gas is manufactured in the following ways:

a. From air

b. From electrolysis of water
a. From air

The mixture of different types of gases is collected and compressed into low volume
with a high pressure. This mixture of gases now changes into liquid state. In this
liquid mixture, there are only nitrogen and oxygen gases. The boiling point of nitrogen
(–196°C) is lower than that of oxygen (–183°C). So, nitrogen gas escapes out leaving only
oxygen gas. Then the oxygen gas is collected in cylinders.

b. From electrolysis of water

When acidified water is electrolyzed, oxygen gas is formed along with hydrogen.

2H2O Electricity H2 + O2
+ H2SO4

Physical Properties of Oxygen

i. Oxygen is a colourless, odourless and tasteless gas.

ii. It is slightly soluble in water.

iii. It is a neutral gas. So, it does not change the colour of litmus paper.

iv. It is non-combustible but supports combustion.

v. It becomes liquid at –183°C and solid at –219°C temperature.

Chemical Properties of Oxygen
i. Combustion

Oxygen does not burn itself but it supports combustion. Objects burn more brightly in

oxygen than in air. Metals like sodium, potassium, calcium, etc. burn in oxygen with

bright flame and form corresponding oxides.

4Na + O2 ∆ 2Na2O (Sodium oxide)
2Mg + O2 ∆ 2MgO (Magnesium oxide)
4K + O2 ∆
2Ca + O2 ∆ 2K2O (Potassium oxide)
2CaO (Calcium oxide)

Modern Concept Science - 9 219

ii. Reaction with non-metals

Non-metals like carbon, sulphur, phosphorus, etc. burn in oxygen and form

corresponding oxides.

C + O2 ∆ CO2 (Carbon dioxide)

S + O2 ∆ SO2 (Sulphur dioxide)

4P +5O2 ∆ 2P2O5 (Phosphorus pentoxide)

iii. Reaction with organic compounds

Organic compounds like hydrocarbon, fat, carbohydrate, etc. react with oxygen and

form carbon dioxide, water and energy.

CH4 + 2O2 ∆ CO2 + 2H2O + Energy

C6H12O6 + 6O2 ∆ 6CO2 + 6H2O + Energy

iv. Reaction with oxides of non-metals

Non-metallic oxides react with oxygen and give corresponding higher oxides.

2NO + O2 2NO2 (Nitrogen dioxide)

2CO + O2 2CO2 (Carbon dioxide)

v. Reaction with hydrogen

Oxygen combines with hydrogen in the presence of electric spark and gives water.

O2 + 2H2 2H2O

vi. Reaction with nitrogen

Oxygen combines with nitrogen at about 3000°C and forms nitric oxide. This reaction
takes place in the atmosphere during lightning.

O2 + N2 3000ºC 2NO (Nitric oxide)

Uses of Oxygen Memory Tips

i. It is used by living organisms to produce energy Oxygen gas is soluble in water.

during respiration. The dissolved oxygen in water is
ii. It is used for combustion of wood, paper, fuel, etc. used by aquatic animals for their
respiration.

iii. It is used for artificial breathing in hospitals.

iv. It is used for making oxy-hydrogen flame for cutting and welding of metals.

v. Mountaineers, deep sea divers, miners and astronauts carry oxygen cylinder for
breathing.

vi. Liquid oxygen is used as a fuel in rocket and missiles.

220 Some Gases

C. NITROGEN GAS

Symbol N

Atomic number 7

Atomic mass 14 7p+ 7p+
Valency 3 and 5 7n0 7n0

Molecular formula N2 Molecular structure of nitrogen
Molecular weight 28
Electronic configuration 1s2, 2s2 2p3

Discovery

Nitrogen gas was discovered by a Scottish scientist Daniel Rutherford in 1772 AD and named
as mephitic air (poisonous gas). Lavoisier studied its properties and named it azota, i.e. gas
having no life. Finally, the name nitrogen was derived from nitre (KNO3), which has nitrogen
as one of the elements.

Occurrence

Nitrogen occurs free as well as in combined state in nature. In free state, it is present in the
atmosphere at about 78.08% by volume. In combined state, it is present in different types of
compounds like ammonia, nitre, ammonium salts, nitrate compounds, etc.

General Methods for Preparation of Nitrogen Gas

Nitrogen gas can be prepared by either of the following methods:
i. From ammonia

Nitrogen gas can be prepared by the reaction of ammonia with chlorine.

8NH3 + 3Cl2 6NH4Cl + N2
ii. From nitric oxide

When nitric oxide gas is passed over heated copper, nitric oxide gets reduced into
nitrogen gas.

2Cu + 2NO 2CuO + N2 Memory Tips

iii. From bleaching powder Calcium hypochloride is an

When bleaching powder Ca(ClO)2 is heated with inorganic compound with formula
ammonia solution, it gives off nitrogen gas. Ca(ClO)2. It is marketed as chlorine
powder or bleach powder for water

3Ca(ClO)2 + 2NH3 3CaCl2 + 3H2O + N2 treatment.

Modern Concept Science - 9 221

Laboratory Preparation of Nitrogen Gas
Principle

In laboratory, nitrogen gas is prepared by heating a mixture of ammonium chloride and

sodium nitrite in solution state.

Ammonium chloride + sodium nitrate Heat sodium chloride + water + Nitrogen gas

NH4Cl + NaNO2 ∆ NaCl + 2H2O + N2
Apparatus required

i. Round bottom flask (R.B. flask) ii. Delivery tube iii. Gas jar

iv. Water trough v. Beehive shelf vi. Burner

vii. Cork viii. Stand ix. Tripod stand

Chemicals required

i. Ammonium chloride (NH4Cl)
ii. Sodium nitrite (NaNO2)

Delivery tube

Stand Thistle
funnel

Round Nitrogen gas
bottom flask
Gas gar
Ammonium chloride Water
+
Water trough
Sodium nitrite Beehive shelf
(NH4Cl+NaNO2)

Tripod stand
Burner

Laboratory preparation of nitrogen gas (N2)

Procedure

i. Make a mixture of ammonium chloride and sodium nitrite and keep it in a round bottom flask.

ii. Make a solution by adding some water and stir.

iii. Arrange the apparatus as shown in the figure.

iv. Supply heat with the help of a Bunsen burner.

On heating the mixture, reaction takes place in two steps as given below and produces

nitrogen gas.

NH4Cl + NaNO2 ∆ NH4NO2 + NaCl
NH4NO2 ∆ 2H2O + N2

NH4Cl + NaNO2 ∆ NaCl + 2H2O + N2

Nitrogen gas thus produced is collected in the gas jar by the downward displacement of water.

222 Some Gases

Precautions

i. The apparatus should be made airtight.

ii. Moderate heat should be supplied during the course of reaction.

iii. The burner should be removed as soon as nitrogen gas starts to evolve.

Test of Nitrogen Gas

i. When a burning match stick is inserted inside the gas jar, the match stick gets
extinguished. It proves that the gas is nitrogen. Carbon dioxide gas also extinguishes
the fire. So some amount of lime water is added into the gas jar. If it does not give milky
white colour, it proves that the gas is nitrogen.

ii. When a burning magnesium ribbon is inserted into the gas jar of nitrogen, it burns in
nitrogen gas forming yellow powder of magnesium nitride (Mg3N2).

Manufacture of Nitrogen Gas

For commercial purpose, nitrogen gas is prepared by following methods:
i. From air

A mixture of different types of gas (air) is collected and liquefied at very low temperature
and high pressure. Now, the liquid gaseous mixture is subjected to fractional distillation.
Liquid nitrogen having low boiling point (–196°C) distills out first leaving the liquid oxygen
of higher boiling point (–183°C). In this way, nitrogen vapour is collected in the cylinder.

ii. From ammonia

For commercial purpose, nitrogen gas can also be prepared by inducing a reaction
between ammonia and chlorine.

8NH3 + 3Cl2 6NH4Cl + N2

Physical Properties of Nitrogen Gas

i. It is a colourless, odourless and tasteless gas.

ii. It is lighter than air.

iii. It is neutral to the indicators.

iv. It neither burns nor supports combustion.

v. It is insoluble in water.

vi. It liquifies at –196°C and solidifies at –210°C.

Chemical Properties of Nitrogen Gas

Nitrogen is a diatomic molecule having triple covalent bonds (N≡N). Due to the presence
of three bonds, it is very less reactive at ordinary temperature. But at high temperature, the
bonds between nitrogen atoms break and induce certain chemical reactions.

Modern Concept Science - 9 223

i. Reaction with hydrogen

Nitrogen combines with hydrogen at about 5000C and 200 to 600 atmospheric pressure
in the presence of iron as a catalyst and molybdenum as a promoter to give ammonia.

N2 + 3H2 500ºC, 200 to 600 atm. 2NH3
Fe/ Mo

ii. Reaction with oxygen

Nitrogen combines with oxygen at about 3000°C to give nitric oxide.
N2 + O2 3000º C 2NO
iii. Reaction with metals
Nitrogen combines with metals to give metallic nitrides.

3Ca + N2 Ca3N2 (Calcium nitride)
2Al + N2 2AlN (Aluminium nitride)
3Mg + N2
Mg3N2 (Magnesium nitride)

Uses of Nitrogen Gas

i. It is used in the manufacture of ammonia gas, nitric acid, nitroglycerine, etc.

ii. It is used in the fuel tanks of aeroplanes to prevent explosion.

iii. It is used in high temperature thermometer to reduce evaporation.

iv. It is used in electric bulbs to provide inert atmosphere.

v. It is used in the manufacture of nitrogenous fertilizers like ammonium nitrate,
ammonium sulphate, etc.

vi. Liquid nitrogen is used as a cooling agent.

FACT WITH REASON

Nitrogen gas in comparatively less reactive at normal temperature, why?

Nitrogen gas is comparatively less reactive at normal temperature because nitrogen is a diatomic molecule
with triple covalent bond between nitrogen atoms. So, it is difficult to break the triple covalent bond at nor-
mal temperature for the chemical reaction.

ANSWER WRITING SKILL

1. Write the name of the lightest gas found on the earth? Name the gas that helps in burning of fire.
Ans: The lightest gas found on the earth is hydrogen gas. The gas that helps in burning is oxygen.
2. W rite the name of gases which are used as a fuel in rocket.
Ans: Mixture of nitrogen, hydrogen and oxygen is usually used as fuel in rocket.
3. What is hydrogenation?
Ans: Hydrogenation is a process of converting vegetable oil into vanaspati ghee by the reaction of hydrogen gas.
4. We use impure zinc granules during laboratory preparation of hydrogen gas. Why?
Ans: We should use impure zinc granules during the laboratory preparation of hydrogen gas to increase the

rate of chemical reaction because pure zinc reacts very slowly with dilute acid.

224 Some Gases

5. We cannot use concentrated sulphuric acid for laboratory preparation of hydrogen gas. Why?

Ans: We cannot use concentrated sulphuric acid for the laboratory preparation of hydrogen gas because
if we use concentrated sulphuric acid, sulphur dioxide gas will be produced instead of hydrogen gas.

6. Why are nitrogen, oxygen and hydrogen gases collected in gas jar by downward displacement of water?

Ans: Hydrogen, oxygen and nitrogen are lighter gases. They have lesser density than water and are insoluble
in water. So, these gases are collected by downward displacement of water.

7. Why are bulbs filled with nitrogen gas but not the oxygen?
Bulbs are filled with nitrogen gas because nitrogen is less reactive gas. It does not burn the filament of
the bulbs. We do not use oxygen in the bulbs because it is highly reactive gas. So, it burns the filament
of the bulb.

8. Why is atmospheric nitrogen very important for living beings?

Ans: Atmospheric nitrogen is fixed into salts of nitrates and nitrites by natural and biological processes.
These salts fall down with rain and mix in soil. Now, these salts are absorbed by the plants and used for
protein synthesis. These proteins are the sources of food for all living beings. Therefore, atmospheric
nitrogen is very important for living beings.

9. Write four uses of oxygen gas.

Ans: Uses of oxygen are listed below:
i) Oxygen is used by all living organisms for respiration and artificial respiration in hospital.
ii) Oxygen is used to produce oxy-hydro flame for welding of metal and also used as a fuel in rocket.
iii) Oxygen supports in burning of hydrocarbons and other substances.
iv) Oxygen is used in sea diving and in mountain climbing.

10. Study the given diagram and answer the following questions.

Delivery tube

Thistle funnel

Cork

Gas jar

Woulfe's bottle Beehive shelf
Granulated zinc
Water trough
Water

i) Which gas is being collected in the gas jar?

Ans: Hydrogen gas is being collected in the gas jar.
ii) How is this gas tested?

Ans: The pure hydrogen gas burns in air with pale – blue flame. So, we need to introduce a burning
match stick near the gas jar. If pale blue flame is formed with pop sound it is hydrogen gas.

iii) Write down the balanced chemical equation involved in this process.

Ans: Hydrogen gas is prepared in laboratory by dissolving granulated zinc in dilute sulphuric acid/

hydrochloric acid.

Zn + dil.H2SO4 Zn SO4+ H2

Modern Concept Science - 9 225

iv) Write down two physical properties of this gas.
Ans: Physical properties of hydrogen gas are:
a) Hydrogen is the lightest gas. It is colourless, odourless and tasteless gas.
b) Hydrogen is neutral to indicator.

STEPS EXERCISE

STEP 1

1. What is atmosphere? Name the different gases present in air with their percentage
composition.

2. Name the chemicals with molecular formula which are required for the laboratory
preparation of hydrogen gas.

3. Name the chemicals with molecular formula which are required for the laboratory
preparation of oxygen gas without heat.

4. Name the chemicals with molecular formula which are required for the laboratory
preparation of oxygen gas by using heat.

5. Name the chemicals with molecular formula which are required for the laboratory
preparation of nitrogen gas.

6. What is hydrogenation? Write with chemical equation.
7. Where is nitrogen gas found in nature?

STEP 2

8. Write down the sure test of hydrogen gas.
9. Explain the sure test of oxygen gas.
10. Write down the sure test of nitrogen gas.
11. Give reason:

a) Copper sulphate is used during laboratory preparation of hydrogen gas.
b) We use impure zinc during laboratory preparation of hydrogen gas.
c) Conc. sulphuric acid is not used during laboratory preparation of hydrogen gas.
d) Hydrogen is used to fill balloons.
e) Oxygen gas is essential for living beings.
f) O xygen is collected by downward displacement of water.
g) N itrogen is filled in the electric bulb.
h) N itrogen gas is used in fuel tanks of aeroplanes.
i) Nitrogen is a less reactive gas.

226 Some Gases

STEP 3

12. Write any three uses of hydrogen gas.
13. Write any three uses of oxygen gas.
14. Write down the uses of nitrogen gas.
15. Write any three physical properties of hydrogen gas.
16. Write any three physical properties of oxygen gas.
17. Write any three physical properties of nitrogen gas.

STEP 4

18. How is hydrogen gas prepared in the laboratory? Give balanced chemical equation
with neat and well labelled figure.

19. Write any four chemical properties of hydrogen gas with balanced chemical equation.
20. How is hydrogen gas manufactured in commercial scale? Describe any two methods in brief.
21. Give any four precautions which should be followed during laboratory preparation of

hydrogen gas.
22. Write down three chemical properties of oxygen gas.
23. Draw a well labelled figure showing the laboratory preparation of oxygen gas by using

heat with its chemical equation.
24. Draw a well labelled figure showing the laboratory preparation of oxygen gas without

using heat with its chemical equation.
25. How is oxygen manufactured for commercial use? Describe in brief.
26. What happens when (write with balanced chemical equation):

a) Hydrogen burns with oxygen?
b) Hydrogen is passed over heated lead oxide?
c) Hydrogen reacts with iodine?
d) Hydrogen reacts with sodium?
e) Oxygen burns with phosphorus?
f) Oxygen reacts with glucose?
g) Oxygen reacts with nitrogen at about 3000°C?
h) Oxygen reacts with magnesium?
i) Metals react with oxygen?
j) Methane reacts with oxygen?
k) Carbon monoxide reacts with oxygen?
l) Nitrogen combines with hydrogen?
m) Aluminium combines with nitrogen?
n) Nitrogen combines with oxygen?

Modern Concept Science - 9 227

o) Study the given figure and answer the following questions.

Hard glass test tube Cork
Potassium chlorate Delivery tube
Mangane+se dioxide

Gas jar

Stand Water trough
Beehive shelf
Bunsen burner

p) Which gas is being collected in the gas jar? Write down the sure test of the gas.
q) Write down the balanced chemical equation involved in this process.
r) Write any three uses of the gas.
27. How is oxygen separated from air? Describe in brief.
28. Draw a well labelled figure showing laboratory preparation of nitrogen gas with its
chemical equation.

29. Write any three chemical properties of nitrogen gas.
30. How is nitrogen gas manufactured? Describe in brief.

31. Study the given figure and answer the following questions:

Delivery tube

Stand Thistle
funnel

Round Gas gar
bottom flask Water

Ammonium chloride Water trough
+ Beehive shelf

Sodium nitrite
(NH4Cl+NaNO2)

Tripod stand
Burner

a) Which gas is being collected in the gas jar? How is this gas tested?
b) Write down the balanced chemical equation involved in this process.
c) Write any two physical properties of this gas.

228 Some Gases

UNIT Estimated teaching periods Theory Practical
5 0
12
Metals

Syllabus issued by CDC Metals

 Introduction to metals
 General properties of metals
 Chemical properties of metals
 Differences between metals and non-metals
 Role of metals in organisms (zinc in enzyme, significance of sodium and potassium ions, negative

impacts of mercury (Hg) and lead (Pb) in human body).

LEARNING OBJECTIVES

At the end of this unit, students will be able to:
 differentiate between metals and non-metals.
 explain the properties of metals and non-metals.
 introduce alloys and metalloids.
 explain the role of metals in living beings (zinc in enzyme, significance of sodium and potassium

ions, negative impacts of mercury (Hg) and lead (Pb) in human body).

Key terms and terminologies of the unit

1. Metals : Metals are those electropositive elements which are good conductors of heat and
electricity.

2. Malleability : The property of a metal due to which it can be beaten into thin sheets is called
malleability.

3. Ductility : The property of a metal due to which it can be drawn into a long wire is called ductility.

4. Metalloids : The elements having the characteristics of both metals and non-metals are called
metalloids.

5. Non-metals : Non-metals are those electronegative elements which are bad conductors of heat
and electricity.

6. Alloy : The homogeneous mixture of two or more metals or metals and non-metals is called alloy.

7. Amalgam : The alloy which is formed by mixing a metal and mercury is called amalgam.

8. Metalloids : The elements having the characteristics of both metals and non-metals are called
metalloids.

9. Sodium-potassium pump: A mechanism of active transport that moves potassium ions into the cell and sodium

ions out of it is called sodium-potassium pump.

10. Hydrargyria: Hydrargyria or mercurialism is a type of metal poisoning caused by exposure to
mercury or its compounds.

Modern Concept Science - 9 229

Introduction

There are altogether 118 elements known till today. It is very difficult to study all these elements
separately. So, on the basis of characteristics, they are divided into three groups, i.e. metals,
non-metals and metalloids. Of the 118 elements, more than 80% of the elements are metals
and the rest of elements are non-metals and metalloids. Elements like iron, copper, aluminium,
silver, gold, etc. are metals. They are good conductors of heat and electricity. Metals are being
used by human beings from pre-historic time. Metals are used for making cooking utensils,
weapons, wires, bodies and parts of vehicles, rods, engines, industrial materials, coins and
many more.

Metals occur in the form of compounds as well as with different types of impurities. They are
separated from various impurities by applying several methods and steps. After the complete
separation, the pure metals are used for different purposes. In this unit, we will discuss the
properties of metals, non-metals and metalloids.

Metals

Metals are those electropositive elements which are good conductors of heat and electricity.
They form electropositive ions by losing electron/s. Examples: Copper, gold, iron, aluminium,
sodium, mercury, calcium, zinc, etc.

a. Physical properties of metals

i. Physical state : Most of the metals exist in solid state at normal temperature but
mercury is found in liquid state.

ii. Hardness : Most of the metals High melting Ductile Lusture
are hard but lithium, sodium point and
and potassium are soft. Physical Malleable
boiling point Properties of
iii. Density : Most metals have Good
high density except lithium, Solid state Metals conductor
sodium and potassium. except Hg of heat and
High electricity
iv. Lustre : Pure metals have Hard and density
brilliant metallic lustre, e.g. gold brittle
has a yellow shine and silver has
a white shine.

v. Conductivity : Metals are
good conductors of heat and
electricity. Therefore, metals
are used for making cooking
utensils and electric wires.

vi. Malleability : The property of a metal due to which it can be beaten into thin
sheets is called malleability. Most of the metals are malleable except lithium,
sodium, potassium, and mercury.

230 Metals

vii. Ductility : The property of a metal due to which it can be drawn into a long wire is called
ductility. Most metals are ductile except lithium, sodium, potassium and mercury.

viii. Melting points and boiling points : Hard metals with high density have high
melting and boiling points but soft metals with low density have low melting and
boiling points.

Hard metals with Melting Boiling Soft metals with Melting Boiling
high density point point low density point point
13260C
1. Iron (Fe) 15350C 27500C 1. Lithium (Li) 1800C
2. Copper (Cu) 882.940C
3. Silver (Ag) 10830C 25670C 2. Sodium (Na) 97.790C
63.50C 7590C
9600C 19550C 3. Potassium (K)

ix. Electric charge : Metals lose electrons from their valence shell and form

electropositive ions. Memory Tips

NaCl Na+ + Cl–

KCl K+ + Cl– Metals which are used to make
coins are called coinage metals.
Na2SO4 2Na+ + SO4– – For example, gold, silver, copper.
CuSO4 Cu+ + + SO4– –

FACT WITH REASON

Why are metals suitable to make utensils?

Metals are suitable to make utensils due to malleability, ductility and conduction of heat.

Why do most of the metals have high melting point and boiling point in general?

Metals have strong metallic bonding. To break this strong metallic bond we need to supply large amount of
heat. So, metals have high melting and boiling point.

b. Chemical properties of metals

i. Reaction with oxygen : When metals are heated with oxygen, they form

corresponding metal oxides. Examples:

4Na + O2 ∆ 2Na2O
4K + O2 ∆ 2K2O
2Mg + O2 ∆ 2MgO
2Ca + O2 ∆
2CaO

ii. Reaction with hydrogen : Some active metals like sodium, potassium, calcium,

etc. react with hydrogen and form unstable hydrides. Examples:

2Na + H2 burn 2NaH (Sodium hydride)

2K + H2 burn 2KH (Potassium hydride)

Ca + H2 burn CaH2 (Calcium hydride)

iii. Reaction with acids : Most of the active metals react with acids and produce

salt and hydrogen gas. Examples:

Modern Concept Science - 9 231

Zn + dil. 2HCl ZnCl2 + H2

Mg + dil. 2HCl MgCl2 + H2

Zn + dil. H2SO4 ZnSO4 + H2

Mg + dil. H2SO4 MgSO4 + H2

Some important metals with their symbol, atomic number, atomic weight and

valency are given below:

S.N. Metals Symbol Atomic Atomic Valency
number weight
1. Lithium Li 1
2. Sodium Na 3 7 1
3. Magnesium Mg 11 23 2
4. Aluminium Al 12 24 3
5. Potassium K 13 27 1
6. Calcium Ca 19 39 2
7. Iron Fe 20 40 2, 3
8. Copper Cu 26 56 1, 2
9. Zinc Zn 29 63 2
10. Silver Ag 30 65 1
11. Gold Au 47 108 1, 3
79 191
12. Mercury Hg 1, 2
80 201

Non-metals

Non-metals are those electronegative elements which are bad conductors of heat and electricity.
Examples: Oxygen, nitrogen, sulphur, chlorine, iodine, etc.

Properties of Non-metals
1. They are electronegative in nature, i.e. they gain electrons during chemical reaction.
2. They are bad conductors of heat and electricity except graphite.
3. They are non-malleable and non-ductile in nature.
4. They do not have metallic lustre except diamond and iodine.
5. They are present in solid, liquid and gaseous state.
6. They do not produce clinking sound. So they are non-sonorous in nature.

Differences between Metals and Non-metals

S.N. Metals S.N. Non-metals

1. Metals are electropositive in nature. 1. Non-metals are electronegative in nature.

2. Metals are malleable. 2. Non-metals are non-malleable.

3. Metals are ductile. 3. Non-metals are non-ductile.

4. They are good conductor of heat and 4. Non-metals are poor conductor of heat

electricity. and electricity except graphite.

232 Metals

5. Most metals exist in solid state at room 5. Non-metals exist in all three states at

temperature except mercury. room temperature.

6. They possess metallic lustre except 6. They do not contain metallic lustre

lithium. except iodine and graphite.

7. They are generally hard except sodium 7. They are generally soft except diamond.

and potassium.

8. They form alloy with other metals. 8. They generally do not form alloys with

other metals.

9. Metals form basic oxides. 9. Non-metals form acidic oxides.

10. Metals react with acid to give salt and 10. Non-metals usually do not form salt

hydrogen gas. and hydrogen gas.

11. Metals generally do not combine 11. Non-metals generally form stable

with hydrogen. If they combine with hydrides.

hydrogen, they form unstable hydrides.

FACT WITH REASON

Why is copper called a metal?
Copper is called a metal because it is malleable, ductile, electropositive, rigid and good conductor of
electricity.
Why is carbon called a non-metal?
Carbon is brittle, not shiny, non-malleable and carbon itself does not conduct electricity. So, carbon is
called a non-metal.

Alloy

The homogeneous mixture of two or more metals or metals and non-metals is called alloy. The
molten mass of two or more metals or non-metals when mixed completely, forms homogenous
mixture. On cooling this mixture, we get a solid mass which is called alloy. The alloy which is
formed by mixing a metal and mercury is called amalgam. The melting point of alloy is always
lower than its component metals. But it has greater hardness and more brittleness.

Properties of alloys
1. Alloys are generally harder and stronger than their components.

2. They have metallic properties like malleability and ductility.

3. They are good conductors of heat and electricity.

4. They are more brittle than their components.

5. They have generally low melting point than that of their components.

FACT WITH REASON

Why is an alloy preferred in constructions than metals?
An alloy is preferred in constructions than the metals because alloy is harder and stronger than its
components.

Modern Concept Science - 9 233

Some alloys and their components

S.N. Alloys Components
1. Brass Copper (70%) and Zinc (30%)
2. Bronze Copper (88%) and Tin (12%)
3. Bell metal Copper (80%) and Tin (20%)
4. Artificial gold (Rold gold) Copper (90%) and Aluminium (10%)
Iron (89.4%), Chromium (10%), Manganese (0.35%)
5. Stainless steel and Carbon (0.25%)

Brass Bronze Bell metal Rold gold Steel

ACTIVITY 1

• Take a few iron nails or a piece of iron. Keep it in a moist place and observe it after 3-4

days. What do you observe?

You can see a reddish-brown layer on the surface of the iron nails.

The formation of reddish-brown scales or powder on the surface of iron when it

comes in contact with moist air is called rusting. As a result of rusting, weight of

metal increases. To protect iron from rusting, we apply several methods like painting,

forming alloys, galvanizing, etc.

x4Fe + H2O + 3O2 x2Fe2O3 . H2O (Rust)

Metalloids

The elements having the characteristics of both metals and non-metals are called metalloids.
For example, silicon, arsenic, antimony, germanium, etc. They are kept in the border line of
metals and non-metals. They are also called semiconductors.

Properties of metalloids
1. Metalloids are poor conductors of heat and electricity.

2. They have lustre, i.e. shiny nature.

3. They do not have malleability and ductility.

4. They form alloys.

FACT WITH REASON

Why is silicon called a metalloid?
Silicon is called a metalloid because it shows some common properties of both metals and non-metals.
It is neither malleable nor ductile like a non-metal but it has metallic luster and forms alloys like metal.

234 Metals

Biological inorganic substances

Generally, six types of non-metals, viz. carbon (C), hydrogen (H), nitrogen (N), oxygen (O),
phosphorus (P) and sulphur (S) are found in the bodies of living organisms. Similarly, different
types of metals are also found in the bodies of living beings. These metals include sodium
(Na), potassium (K), calcium (Ca), zinc (Zn), magnesium (Mg). These metals and non-metals
are found in the form of compounds. Substances like protein, nucleic acid, lipids, etc. are
formed from these elements, which are also known as biological inorganic substances. These
elements have a great role in the bodies of living organisms.

Role of Metals in Organisms

Among the above mentioned metals, Na, Mg, K and Ca are found in large amount whereas
metals like Mn, Fe, Co, Cu, Zn and Mo are found in small amounts.

Zinc in Organisms

Zinc is a very important metal though it is found in small amount in the bodies of organisms.
It is essential to life. It plays an important role in biological processes of all living organisms
(humans, animals, and plants). Zinc is crucial for cell division, protein synthesis, the immune
system and growth.

Zinc in Enzyme

About 300 enzymes in human body contain zinc. About 2-3 gram of zinc is found in
human body. Zinc is found in almost all organs of human body. It is found in cytoplasm,
cells, tissues, bones, organs, etc. About 90% of zinc of the body is found in muscles and
bones. A significant amount of zinc is found in prostate gland and semen. Similarly, a
large amount of zinc is found in retina which decreases with age and finally the person
cannot see things clearly. In the body of living beings, zinc is found in the form of
compounds and ions.

Role of zinc in human body

1. In human body, zinc is essential for development of embryo to increase height
and weight of the body.

2. Zinc is essential for development of bones.

3. It is essential to regulate menstrual cycle in women.

4. It is essential to increase sex power/fertility in men.

5. It is essential to treat anorexia, psoriasis and neurodermitis.

6. It is essential to increase immune system. Memory Tips
7. It is essential to taste food items and smell things.
8. It is essential to prevent pneumonia, diarrhoea Foods high in zinc include red
meat, poultry, toasted wheat
and other infectious diseases. items, spinach, pumpkin seeds,
9. It is essential to cure wounds and form skin cells. nuts, beans, mushrooms, etc.

Modern Concept Science - 9 235

FACT WITH REASON

Why is zinc important in a child’s diet?

Zinc is a trace element that is essential for cell division. It helps in normal growth and development of in-
fants and children. Zinc improves the immunity of the body and resistance against infections.

Importance of Sodium and Potassium Ions Memory Tips

Among the different metals found in human body, sodium Neurons and muscle cells are
and potassium play a significant role. These metals are found electrically excitable cells. Ions
in the form of ions inside and outside cells. Nervous system (Na+, K+) in our body cause an
can work only due to the presence of metallic ions as they electrical impulse. Neurons send
contain charges. messages electrochemically.

Sodium-potassium pump

Various metabolic activities like nerve impulse transmission occur in the body due

to the exchange of ions in cells. When we stimulate an excitable cell the sodium ions

present outside of a cell diffuse into the cell through sodium channels and potassium

ions diffuse out through potassium channels. Cell
Diffusion of ions is followed by an active transport exterior

of sodium ions and potassium ions through sodium-

potassium pump. This mechanism sends three sodium

ions out of the cell and brings two potassium ions inside

of the cell at the same time. Thus, a mechanism of active Plasma
membrane

transport that moves potassium ions into the cell and Cell interior
sodium ions out of it is called sodium-potassium pump.
Sodium-potassium pump
Role of sodium-potassium pump
Memory Tips
Sodium-potassium pump is very important for human
body. It is essential to exchange information between Sodium sources: Sodium is
neurons and brain, to regulate heart beat and body found in table salt, baking
temperature, to keep muscles sound, to control pH of soda, meat, fish, eggs, milk,
olives, celery (Ajvawain), beet
solutions in the cells, etc. Various disorders like migraine, (chukundara), etc.
muscle spasm, paralysis, etc. occur in the body due to Potassium sources: Many foods
irregularity in sodium and potassium pump. Therefore, contain potassium, including all
there should be proper balance in sodium and potassium meats, some types of fish, many

ions in the human body. fruits, vegetables, and legumes,

Harmful Effects of Mercury and Lead etc.

a. Mercury contamination Memory Tips

The poisonous effect of mercury in human body is Hydrargyria or mercurialism is a
called hydrargyria or mercurialism. Minamata disease type of metal poisoning caused
is a neurological syndrome caused by severe mercury by exposure to mercury or its
poisoning. It was first discovered in Minamata city compounds.
in Japan, in 1956. It was caused by the release of

236 Metals

methylmercury in the industrial wastewater from chemical factories.

Sources: Bio-accumulation in seafood carries over mercury into humans. Fish can be
contaminated by eating other mercury containing organisms. The consumption of such
a fish is the most significant cause for mercury poisoning. Humans can also develop
mercury poisoning by inhaling mercury contaminated air.

Effects: One drop of mercury may block blood vessels and cause death of the victim. The
compounds of mercury damage the brain. Similarly, they weaken the ability to speak,
hear and see things. Mercury also affects the foetus. The compounds of mercury pass
easily through placenta and affect the growth and development of the foetus adversely.
Mercury also affects the development of child's brain adversely.

FACT WITH REASON

Mercury is dangerous to humans, why?
Mercury is a metal known to be highly toxic, especially due to its ability to damage the central nervous
system. So, mercury is dangerous to humans.

b. Lead contamination Memory Tips

Lead poisoning is an environmental hazard that is Humans can be exposed
capable of causing mental retardation, behavioral to lead by eating food and
disturbance, and brain damage. Exposure to lead drinking water containing
can occur by contaminated air, water, dust, food, or lead. It may be from dishes or
consumer products. glasses that contain lead. It
may be due to Inhaling lead
Sources: Lead can still be found in some cosmetic lip dust from lead-based paints
products, colouring pigments, lead-based paints used or lead-contaminated soil.
in older homes, contaminated soil, household dust,

drinking water pumped through leaded pipes, lead crystal glass, lead-glazed pottery,
airplane fuel, some toys, and some inexpensive metal jewelry.

Effects: Lead (Pb) affects almost all the organs of human body. It spreads throughout the
body like other useful metals. It affects the brain adversely. Symptoms like headache,
abdominal pain, change in behaviour, lack of brain development, etc. occur in children.
Blood cannot combine with oxygen due to the presence of lead which causes anaemia.
Lead accumulates in bones which affects the formation of blood cells in bone marrow.
It also affects calcium absorption by bones which weakens them. Therefore, we should
avoid the food items containing lead.

FACT WITH REASON

Lead poisoning causes anaemia. Give reason.

Acute poisoning of lead can damage red blood cells in the bloodstream. It limits their ability to carry oxygen
to the organs and tissues that need it, thus it causes anaemia.

Lead is dangerous to humans, why?

Once when lead gets into a person's system, it is distributed throughout the body just like other useful
metals such as iron, calcium, and zinc. Lead can cause harm wherever it lands in the body. So, lead is
dangerous to humans.

Modern Concept Science - 9 237

ANSWER WRITING SKILL

1. Which non-metals have metallic luster?
Ans: Graphite and iodine are non-metals which have lustre.
2. Name two metalloids.
Ans: Silicon, antimony are two metalloids.
3. Name the hardest non-metal.
Ans: Diamond (purest form of carbon) is the hardest metal.
4. W rite the molecular formula of rust.
Ans: The molecular formula of rust is Fe2O3. nH2O.
5. What is sodium-potassium pump?
Ans: A mechanism of active transport that moves potassium ions into the cell and sodium ions out of it

is called sodium-potassium pump.
6. Define coinage metals.
Ans: Metals which are used to make coins are called coinage metals. These are shiny, soft and malleable.

For example, copper, silver and gold.
7. Why are metals used to make electrical wires?
Ans: Metals are used to make electrical wire because:

i) They are good conductor of electricity.
ii) They can be drawn into wires.
iii) They have low resistance.
8. Aluminium is used to make pressure cooker. Why?
Ans: Aluminium is used to make pressure cooker because:
i) It is malleable. It can be changed into desired shape.
ii) It is good conductor of heat.
iii) It is tensile. It does not break easily and makes strong pots.
9. Why are gold and silver used to make ornaments?
Ans: Gold and silver are used to make ornaments because:
i) Gold and silver have attractive colour and luster.
ii) Gold and silver are malleable. So, they can be changed into desired shape easily.
iii) Gold and silver are less affected by air and water.
10. What are the uses of metals?
Ans: Uses of metals are given below:
i) Metals are used to make utensils, electrical wires, electronic devices etc.
ii) Metals are used to make coins, jewelry, etc.
iii) Metals are also used in construction of bridges, buildings etc.
iv) Metals are also used to make body parts of planes, rockets, vehicles etc.
11. Name the metals and non-metals essential for our body. Write about the role of these elements in
human body.

238 Metals

Ans: Carbon, hydrogen, oxygen, sulpher, phosphorus and nitrogen are six main non-metals present in
human body. Whereas zinc, potassium, magnesium, calcium and sodium are main metals present
in human body.

The above metals and non-metals have very important role in human body. These elements are found
in the form of compounds such as protein, carbohydrates, lipid, etc. They help to form more than 300
types of enzymes in our body. They help to regulate many metabolic activities. These minerals also help
to prevent various diseases. They also help in proper physical and mental growth and development of
the body.

STEPS EXERCISE

STEP 1

1. Define b) Malleability c) Ductility d) Metalloids
a) Metals Rusting

e) Non-metals f) Alloy g) Amalgam h)

2. Very Short Answer Questions

a) Write any four examples of mental.

b) Give any three examples of non-metals.

c) Write any three examples of metalloids.

d) Write down the composition of metals in brass and bronze.

3. Name the following:
a) A metal having high melting and boiling point

b) A metal that exists in liquid state

c) A non-metal that conducts electricity

d) An alloy made of copper and tin

e) A metalloid other than silicon

f) A non-metal having metallic lustre

g) A metal which is non-malleable and non-ductile

STEP 2

4. Differentiate between:
a) M etals and Non-metals
b) Metals and Metalloids
c) Non-metals and Metalloids
d) Metals and Alloys

5. Give reason:
a) C opper is called a metal.
b) Carbon is called a non-metal.

Modern Concept Science - 9 239

c) I ron and aluminium are used for making cooking utensils.
d) Silicon is called a metalloid.
e) Non-metals are not suitable for making electric wires.
f) Most of the metals have high melting and boiling point.
g) An alloy is preferred in constructions than metals.
h) Zinc is important in a child’s diet.
i) Mercury is dangerous to humans.
j) Lead poisoning causes anaemia.
k) Lead is dangerous to humans.
6. Name any five metals and five non-metals that are found in the bodies of living
organisms.

STEP 3

7. What happens when (write with balanced chemical equation):
a) Sodium reacts with hydrogen?
b) Magnesium reacts with dilute sulphuric acid?
c) C alcium reacts with oxygen?
d) P otassium reacts with hydrogen?

8. Write any four physical properties of metals.
9. Write any four physical properties of non-metals.
10. Write any three properties of alloys.
11. Write any three properties of metalloids.
12. Write any three chemical properties of metals.

STEP 4

13. Describe the role of zinc in human body in brief.
14. What is meant by sodium-potassium pump? Describe the importance of sodium and

potassium ions in human body.
15. Write any three negative impacts each of mercury and lead on human body.

240 Metals

UNIT Estimated teaching periods Theory Practical
5 0
13
Carbon and its Compound

Syllabus issued by CDC Diamond

 Carbon in common materials
 Sources of carbon
 Nature of carbon
 Physical properties of carbon
 Chemical properties of carbon
 Organic and inorganic compounds
 Differences between organic and inorganic compounds

LEARNING OBJECTIVES

At the end of this unit, students will be able to:
 introduce carbon and its compounds.
 explain the physical and chemical properties of carbon.
 explain the allotropes of carbon.
 differentiate between organic and inorganic compounds.

Key terms and terminologies of the unit

1. Catenation property of carbon : Carbon is one of the unique elements which can join with each other to form a

long chain of carbon atoms which is called catenation property of carbon.

2. Allotropes : The different forms of an element having similar chemical properties but different

physical properties are called allotropes

3. Allotropy : The characteristic by virtue of which carbon exists in various forms in nature is

called allotropy.

4. Diamond : Diamond is one of the purest forms of carbon. It is non-conductor, transparent,

colourless and precious crystalline solid.

5. Graphite : Graphite is a soft and the purest form of carbon. It is dark grey and crystalline

powder with metallic lustre. It has free mobile electrons. So it is a good conductor

of heat and electricity.

6. Organic compounds : The compounds formed by reaction of carbon with elements like hydrogen,

oxygen, nitrogen, etc. are called organic compounds.

7. Organic chemistry : The branch of chemistry in which we study about organic compounds is called

organic chemistry.

8. Inorganic compounds : The compounds which are derived from minerals are called inorganic compounds.

9. Inorganic chemistry : The branch of chemistry in which we study about inorganic compounds is called

inorganic chemistry.

10. Hydrocarbons : Hydrocarbons are the chemical compounds made from hydrogen and carbon

with covalent bond between them.

Modern Concept Science - 9 241

Introduction

Carbon is one of the most important and unique non-metallic elements. The word carbon has
been derived from the Latin word 'carbo', which means shoot or charcoal. Carbon is widely
distributed on the earth in free as well as in combined state. In free state, it is present in
diamond, graphite, charcoal, coal, etc. whereas in combined state, it is present in carbon
monoxide, carbon dioxide, carbonates, carbohydrates, proteins, fats, nucleic acids, petroleum,
natural gas, etc. The bodies of living beings contain carbon and its compounds in abundant
quantity. When we burn these carbon containing compounds, we get black shoot, smoke,
charcoal, etc.

Carbon occurs in different forms with different physical properties which are called allotropes.
Diamond is one of the hardest allotropes which is transparent, brilliant and precious whereas
graphite is another soft, slippery, black and greasy allotrope of carbon.

ACTIVITY 1

Objective : To prove sugar contains carbon. Water droplets
Materials required : Sugar, hard glass test tube and source of heat

(Bunsen burner) Sugar
Procedure : Keep some sugar in the hard glass test tube and heat

with the help of Bunsen burner. Burner

Observation

1. Initially at about 186°C sugar melts and gives yellowish

syrup.

2. On further heating, it turns into a brownish mass with good smell which is called

caramel.

3. At final stage, the mass is converted into black matter called charcoal, i.e. carbon.

Conclusion : The above activity shows that sugar contains carbon.

Structure of Carbon Atom

The nucleus of carbon atom consists of six protons and six neutrons. Six electrons revolve
around the nucleus in two orbits, viz. K and L. The shell K consists of two electrons whereas
the shell L consists of four electrons.

Symbol = C

Atomic number = 6

Atomic mass = 12

Electronic configuration 6p+
6n0
Shell K L

No. of electrons 2 4

Position in periodic table: Period – 2, Group – IVA Structure of carbon atom

242 Carbon and its Compound