science 9

5. Dilute sulphuric acid should be used instead of concentrated
sulphuric acid because concentrated sulphuric acid produces
sulphur dioxide instead of hydrogen gas when it reacts with zinc.

Test of hydrogen
1. Hydrogen burns with a pale-blue flame at the opening of the
gas jar.
2. When a lighted candle is taken to the mouth of the gas jar,
containing hydrogen gas, the candle gets extinguished
immediately producing a pop sound. This proves that the
gas in the jar is hydrogen.

Manufacture of hydrogen gas

Hydrogen gas is manufactured in industrial scale by using different
methods. Some of them are explained below:

1. By the reaction of methane gas with steam

Hydrogen gas is prepared in large scale by the reaction of methane
with steam at 1200°C and under 30 atmospheric pressure in the
presence of nickel as catalyst.

Methane + Water vapour →Carbon monoxide + Hydrogen

CH4 (g) + H2O (g) → CO (g) + 3H2 (g)
The mixture of carbon monoxide and hydrogen is called water gas.
It can be used as fuel.
A catalyst is a chemical compound which increases or decreases
the rate of chemical reaction without being consumed itself. The
catalyst which increases the rate of chemical reaction is called
positive catalyst whereas the catalyst which decreases the rate of
chemical reaction is called negative catalyst. In this case, nickel is
a positive catalyst.

2. By the electrolysis of water

The hydrogen gas can be produced in large scale by the electrolysis
of water. When electricity is passed through acidified water, it
dissociates into hydrogen and oxygen. Both gases can be collected
in separate vessels.

2H2O electrolysis 2H2↑ + O2↑
Mechanism of electrolysis

When dilute H2SO4 is added in water, it ionizes as follows:
H2O electrolysis H+ + OH−

197 Times' Crucial Science Book - 9

At cathode;
H+ +e H (Nascent hydrogen)

H + H → H2↑

Nascent hydrogen is the newly formed hydrogen. In other words, it
is the hydrogen at the moment of its origin. It is in atomic form and
is highly reactive. The nascent hydrogen immediately reacts with
another hydrogen atom to form molecular hydrogen which is less
reactive.

Properties of hydrogen

Physical properties
1. It is colourless, odourless and tasteless gas.
2. It is slightly soluble in water.
3. It is highly combustible gas. It burns with pale blue flame.
4. It is neutral to litmus paper.
5. It is the lightest and simplest gas.
6. Its boiling point is −253°C and melting point is −259°C.

Chemical properties

1. Hydrogen burns with oxygen to produce water.
2H2 + O2 ∆ 2H2O
water

2. Active metals like sodium, potassium, calcium, barium, etc
react with hydrogen to form hydride.
2Na + H2 300°C 2NaH
Sodium hydride
Ca + H2 300°C CaH2

Calcium hydride (Hydrolith)

3. Hydrogen reacts with halogens under different conditions to
form respective halides.

H2 + F2 dark 2HF
H2 + Cl2 light 2HCl
H2 + Br2 400°C 2HBr
H2 + I2 400°C 2HI

Times' Crucial Science Book - 9 198

4. Hydrogen reduces metallic oxides to their metals. When dry
hydrogen is passed over heated metallic oxides like copper
oxide (CuO), lead oxide (PbO), zinc oxide (ZnO), etc, the oxides
are reduced to pure metals. For example,

CuO + H2 ∆ Cu + H2O
ZnO + H2 ∆ Zn + H2O
PbO + H2 ∆ Pb + H2O

5. Hydrogen reacts with nitrogen to produce ammonia gas at
about 450°C and under 200-600 atmospheric pressure. In
this reaction, iron works as a catalyst and metal oxide as a
promoter.

N + 3H 2 NH450°C, 200-600 atm 3
2 2 Fe (catalyst), MO (promoter)

This process is known as Haber’s process.

6. When a vegetable oil is heated with hydrogen gas in the presence
of nickel catalyst, solid fat (vanaspati ghee) is produced. The
process of producing vansapati ghee is called hydrogenation.

Vegetable oil + H2 200°C, 8-10 atm Vanaspati ghee
Nickel

7. Hydrogen combines with some non-metals at high temperature.

For example, ∆ CH4
Methane
C +2H2

S + H2 ∆ H2S

Uses of hydrogen
1. It is used to fill the balloons as it is the lightest gas.
2. It is used as fuel in the rockets at liquid state.
3. It is used to manufacture ammonia gas.

4. Hydrogen is used to produce vanaspati ghee from vegetable oil.
5. It reduces metallic oxides into corresponding metals. So, it is

used as a reducing agent in lab.
6. It is used in welding and cutting of metals. When the

mixture of hydrogen and oxygen burns in a welding torch,
it produces the temperature of about 3000°C. The flame

which is produced during the burning of hydrogen in oxygen
is called oxy-hydrogen flame.

199 Times' Crucial Science Book - 9

Learn and Write

1. Generally hydrogen is not found in the air in free state.
Why?

Hydrogen is more reactive gas. Therefore, it reacts with other
elements. Moreover, it is the lightest gas. Therefore, it is not
generally found in atmosphere.

2. Impure granulated zinc is used instead of pure zinc
during lab preparation of hydrogen gas. Why?

Pure zinc reacts with dilute sulphuric acid slowly but the
granulated zinc reacts with dilute sulphuric acid fast.
Therefore, granulated zinc is used instead of pure zinc during
lab preparation of hydrogen gas.

3. Hydrogen gas is collected by downward displacement
of water. Why?

Hydrogen gas is lighter than water and is insoluble in water.
Therefore, it is collected in the gas jar by the downward
displacement of water.

Main points to remember

1. Atmosphere consists of different gases like nitrogen, oxygen, carbon
dioxide, inert gases, water vapour, etc.

2. Hydrogen is the lightest and simplest gas.
3. Hydrogen gas is obtained by the reaction of metals with acids.
4. Hydrogen gas is prepared in the laboratory by the action of zinc with

dilute sulphuric acid.
5. Hydrogen is a colourless, odourless and tasteless gas. It is insoluble in

water.
6. Hydrogen burns with oxygen to produce water.
7. Hydrogen reacts with nitrogen at 450°C and 200−300 atmosphere

in the presence of finely divided iron with little molybdenum to
produce ammonia.

Exercise

1. Answer these questions in very short.
a. What is atmosphere?
b. What is the position of hydrogen in the periodic table?
c. State the principle of laboratory preparation of hydrogen gas?
d. How do you test the hydrogen gas?
e. Why is dilute (not conc.) H2SO4 used in the lab preparation

Times' Crucial Science Book - 9 200

of hydrogen gas?
f. Write down the melting and boiling point of hydrogen gas.
g. What is nascent hydrogen?
h. State any two uses of hydrogen gas.

i. Define: (ii) Positive catalyst
(i) Catalyst (iv) Hydro genation
(iii) Reducing agent

2. Give reasons:
1. Generally hydrogen gas is not found in air.
2. Hydrogen is collected in the gas jar by downward
displacement of water.
3. Impure zinc is used instead of pure zinc during the
laboratory preparation of hydrogen gas.
4. The lower end of thistle funnel should be dipped in solution.

3. Study the following figure and answer the questions:
a. Which gas is being collected in the
gas jar?
b. Write the principle used in the
given process.
c. What happens when pure zinc is
used instead of impure zinc?
d. What happens when thistle funnel
is not dipped in the reaction
mixture?
e. Draw the diagram and label all the parts.

4. What happens when:
a. Hydrogen is mixed with chlorine is sunlight.
b. Hydrogen is passed through heated copper oxide
c. Hydrogen burns with oxygen.
d. Hydrogen reacts with sodium.
e. A mixture of hydrogen and nitrogen is passed over iron
catalyst heated at 450°C.

201 Times' Crucial Science Book - 9

Oxygen

Symbol: O Atomic number: 8

Molecular formula: O2 Atomic weight: 16
Valency: 2 Molecular weight: 32

Position in periodic table: Group VIA, Period 2

p=8 p=8 p=8
n=8 n=8 n=8

Oxygen atom Oxygen molecule

Oxygen is an important constituent of air. It was prepared by a
British scientist Joseph Priestley in 1774 AD. He prepared oxygen
gas by heating red oxide of mercury. Later Lavoisier made the
systematic study of properties of oxygen and named it oxygen.
Previously, it was known as fire gas because it is necessary for
burning. Lavoisier experimentally verified that it constitutes 21%
of the total volume of air. Oxygen constitutes about 47.6% of the
earth’s crust by weight .

General methods of preparation of oxygen gas

1. By heating metallic oxides

Oxygen can be prepared by heating the oxides of mercury,
silver, etc.

2HgO ∆ 2Hg + O2↑

Mercuric oxide Mercury Oxygen

2Ag2O ∆ 4Ag + O2↑
Silver oxide Silver Oxygen

2. From metallic peroxides

When metallic peroxides react with water, metal hydroxide
and oxygen are produced. For example,

2Na2O2 + 2H2O → 4NaOH + O2↑

Sodium peroxide Water Sodium hydroxide

Times' Crucial Science Book - 9 202

3. From water

Oxygen gas can be produced by electrolysis of water in the
presence of sulphuric acid as electrolyte. Hydrogen gas is also
produced in this reaction.

2H2O electrolysis 2H2↑ + O2↑

Laboratory preparation of oxygen gas

Oxygen gas is produced in the laboratory by two different methods.

They are: a. by heating b. without heating

1. By heating

Principle:

Oxygen is prepared in the laboratory by heating potassium chlorate

(KClO3) in the presence of manganese dioxide as catalyst.

2KClO3 250°C 2KCl + 3O2↑
MnO2

Apparatus required:

Bunsen burner, hard glass test tube, delivery tube, stand, water
trough, beehive shelf, gas jar, cork, etc.

Chemicals required

1. Potassium chlorate (KClO3) 2. Manganese dioxide (MnO2)

Procedure:
1. Mix powdered potassium chlorate and manganese dioxide in the ratio
of 4:1 by weight.
2. Place the mixture in the hard glass test tube and fit the apparatus as
shown in figure.

Hard glass test tube Delivery tube Oxygen gas
Mixture of Gas jar
MnO2 + KClO3
Trough
Burner Water

Laboratory preparation of oxygen gas

203 Times' Crucial Science Book - 9

3. Heat the mixture with the Bunsen burner. Now, potassium chlorate
dissociates to produce potassium chloride and oxygen, The oxygen gas
passes through delivery tube to the gas jar and gets collected in the gas
jar by the downward displacement of water.

Precautions
1. Manganese dioxide (catalyst) should be used in pure form. If impure
manganese dioxide is used, the carbon particles present in manganese
dioxide may burn and explosion may take place.
2. The hard glass test tube should be clamped in the stand in an inclined
position so that the evaporated moisture may not return to the mixture
after condensation.
3. The apparatus should be made air tight.

2. Without heating
Principle:
Hydrogen peroxide gets decomposed to water and oxygen without
the use of heat. In laboratory, oxygen gas is prepared by the
decomposition of hydrogen peroxide using manganese dioxide as
catalyst.

2H2O2 MnO2 2H2O + O2↑

Apparatus required:

Conical flask, thistle funnel, delivery tube, water trough, beehive
shelf, gas jar, cork, etc.

Chemicals required:
1. Hydrogen peroxide (H2O2)
2. Manganese dioxide (MnO2)
3. Water (H2O)

Hydrogen peroxide

Funnel with a stopper

Oxygen gas

Conical flask Delivery Gas jar
tube
Water
Beehive shelf

Laboratory preparation of oxygen gas

Times' Crucial Science Book - 9 204

Procedure:
1. Fit the apparatus as shown in figure and put the mixture of MnO2 and
water into the conical flask.
2. Pour hydrogen peroxide through a funnel having a stopper to the mix-
ture of manganese dioxide and water.
3. Hydrogen peroxide decomposes to give oxygen as it comes in contact
with MnO2. Thus produced oxygen passes through the delivery tube
and gets collected in the gas jar by downward displacement of water.

Test of Oxygen

Take a burning matchstick to the mouth of the gas jar containing
the gas. If the matchstick continues burning with brighter flame,
the gas in the gas jar is oxygen. It is the only gas which supports
burning but doesn’t burn itself.

Manufacture of oxygen gas

1. From liquid air
Oxygen and nitrogen are the main components of air. These gases
can be separated from each other by cooling them to liquid state.
These gases have different boiling points. The boiling point of
nitrogen is −196°C and that of oxygen is −183°C. When liquid air is
subjected to fractional distillation, nitrogen moves away leaving O2.

2. By the electrolysis of water

Oxygen can be produced in lab as well as in large scale by electrolysis
of water. When electricity is passed through acidified water, it
decomposes water into hydrogen and oxygen.

2H2O electrolysis 2H2 + O2

Properties of oxygen

Physical properties
1. It is a colourless, odourless and tasteless gas.
2. It is slightly soluble in water, The aquatic organisms breathe in oxygen
dissolved in water.
3. It is neutral to litmus paper.
4. It is slightly heavier than air.
5. It solidifies at − 219°C and liquefies at −183°C.

Chemical properties

1. If the metals such as sodium, magnesium, potassium, etc are

205 Times' Crucial Science Book - 9

burnt in oxygen, metallic oxides are produced.

2Mg + O2 ∆ 2MgO
O2 ∆ Magnesium oxide
Magnesium
2CaO
2Ca + Calcium oxide

Calcium

However, gold and platinum do not combine with oxygen while
heating.

2. If nitrogen is heated with oxygen at very high temperature,
nitric oxide is produced.
N2 + O2 2000°C−3000°C 2NO

Nitric oxide

3. Non-metals form their respective oxides when burnt in oxygen.
Carbon, phosphorus, sulphur, etc are some common non-metals
that form oxides on burning.

C + O2 ∆ CO2

Carbon dioxide

P4 + 5O2 ∆ 2P2O5

Phosphorus pentoxide

S + O2 ∆ SO2

Sulphur dioxide

4. When iron is strongly heated with oxygen, ferroso-ferric oxide
is produced.
3Fe + 2O2 ∆ Fe3O4

Ferroso - ferric oxide

5. Ammonia gas burns in oxygen with greenish yellow flame to
produce nitrogen and water vapour.

4NH3 + 3O2 → 6H2O + 2N2↑
6. Hydrocarbons burn with oxygen to produce CO2, water vapour

and heat energy.
CH4 + 2O2 ∆ CO2 + 2H2O + heat

Times' Crucial Science Book - 9 206

7. When glucose present in cells of our body burns with oxygen, it
produces carbon dioxide, water vapour and energy.

C6H12O6 + 6O2 →6CO2 + 6H2O + heat

This reaction occurs during respiration. It is the source of energy for the body.

Uses of oxygen
1. Oxygen is used by all living things for respiration. It helps to produce
energy by the oxidation of digested food.
2. It is used to provide artificial respiration for patients in hospitals.
3. Liquefied oxygen is used in rocket as a part of fuel.
4. The burning of oxygen and acetylene gas produces large amount of
heat. So, it is used for welding and cutting metals. The flame produced
due to the burning of acetylene with oxygen is called oxyacetylene flame.
5. Mine workers, sea-divers and mountaineers carry oxygen cylinders for
respiration.

Learn and Write

1. Aquatic animals can survive in water. Why?
Oxygen gas gets dissolved in water. The aquatic animals absorb
the dissolved oxygen for breathing. Thus, aquatic animals can
survive in water.

2. Manganese dioxide is used in the preparation of oxygen gas. Why?
Manganese dioxide (MnO2) works as a positive catalyst during the
lab preparation of oxygen gas. MnO2 increases the rate of chemical
reaction thereby increasing the rate of production of oxygen gas.

Main points to remember

1. Oxygen gas was prepared by Joseph Priestley in 1774 AD.
2. Oxygen gas is prepared by heating metallic peroxides, metallic oxides,

electrolysis of water, etc.
3. Oxygen gas is prepared in the laboratory by heating potassium

chlorate in the presence of manganese dioxide.
4. Oxygen is slightly soluble in water and neutral to the litmus paper.
5. Oxygen is used by all living things for respiration.
6. Oxygen burns with acetylene producing high temperature which is

used for welding metals.

Exercise

1. Answer the questions in very short.
a. What is the position of oxygen in the periodic table?
b. How do you test oxygen gas?

207 Times' Crucial Science Book - 9

c. How do aquatic animals get oxygen?
d. What is the role of MnO2 in the lab preparation of oxygen gas?
e. Why is oxygen collected by downward displacement of water?

2. Give reasons:
a. Manganese dioxide is required in the laboratory preparation
of oxygen gas though it does not take part in reaction.
b. When a burning matchstick is introduced to the mouth of
gas jar containing oxygen, it burns brightly.

3. What happens when
a. Silver oxide is heated?
b. Potassium chlorate is heated with manganese dioxide?
c. Carbon is heated with oxygen?
d. Magnesium is burnt in oxygen?
e. Hydrogen peroxide is decomposed in the presence of
manganese dioxide?
f. Iron is heated with oxygen?

4. Diagrammatic question:
a. Draw the atomic and molecular
structure of oxygen.
b. How do you prepare oxygen in
laboratory by using heat? Explain
the principle with well-labeled
diagram.
c. How do you prepare oxygen in lab
without using heat? Explain the principle with well labelled
diagram.
d. Study the diagram given below and answer the questions.
i) Which gas is being collected in the gas jar?
ii) How do you test the gas collected in gas jar?
iii) Write the balanced chemical equation for the
reaction involved in this process.
iv) Name the catalyst used in this process. Is this a
negative or positive catalyst? Why?
v) Why is delivery tube not dipped in reaction mixture?

Project Work

Study the method of lab preparation of oxygen given in the text and arrange
the apparatus. The prepare oxygen gas yourself and study its properties.

Times' Crucial Science Book - 9 208

Nitrogen

Symbol: N Atomic number: 7

Molecular formula: N2 Atomic weight: 14
Valency: 3 and 5 Molecular weight: 28

Position in periodic table: Group VA, Period 2

p=7 p=7 p=7
n=7 n=7 n=7

Nitrogen atom Nitrogen molecule

A Scottish scientist Daniel Rutherford discovered nitrogen in 1772
AD and named it mephitic air (poisonous air). Lavoisier studied its
properties such as it is neither combustible nor the supporter of
combustion. He also proved that it does not take part in respiration.
He named it ’azote’ which means no relation with life. The name
’nitrogen’ was given by J.A.C Chaptal in 1790.
Nitrogen occurs in free as well as combined state in nature. Free
state of nitrogen occupies about 78% of the total volume of air.
Nitrogen is an essential component of proteins in all plants and
animals in combined state. It is also present in enzymes, RNA,
DNA, etc. It is also found in ammonia and ammonium salts.

General methods of preparation of nitrogen gas

1. From nitric oxide: Nitrogen is produced when nitric oxide is
heated with copper.

2Cu + 2NO ∆ 2CuO + N2↑

2. From ammonia: When ammonia gas reacts with chlorine,
nitrogen gas is produced.

8NH3 + 3Cl2 → 5NH4Cl + N2↑
3. From ammonium dichromate

Nitrogen gas can be obtained by heating ammonium
dichromate.

(NH4)2Cr2O7 →N2 + Cr2O3 + 4H2O

209 Times' Crucial Science Book - 9

4. By passing air through heated copper

Air freed from CO2 and moisture is passed over heated copper
which combines with oxygen of air to form oxide. But the
nitrogen is left unreacted. The left nitrogen can be collected by
downward displacement of water.

2Cu + (O2, N2) → 2CuO + N2
Laboratory preparation of nitrogen gas
Principle:
Nitrogen is prepared in the laboratory by gently heating a mixture
of equimolar solutions of sodium nitrite and ammonium chloride.
The evolved nitrogen is collected by downward displacement of
water.

NaNO2 + NH4Cl ∆ NaCl + 2H2O + N2↑

Actually, the above reaction takes place in two steps as:

NaNO2 + NH4Cl → NH4NO2 + NaCl

NH4NO2 → 2H2O + N2↑

Apparatus required:

Bunsen burner, stand, wire gauge, tripod stand, round bottom
flask, cork, delivery tube, beehive shelf, water trough, gas jar, etc.

Chemicals required:
1. Ammonium chloride (NH4Cl)
2. Sodium nitrite (NaNO2)
3. Water (H2O)

Stand Thistle funnel Nitrogen gas
Delivery
Round bottom flask tube Gas jar
Solution of ammonium
chloride and sodium nitrite Wire Trough
gauge Water
Tripod stand Bee-hive shelf

Times' Crucial Science Book - 9 Burner
Lab preparation of nitrogen gas

210

Procedure:
1. Pour the mixture of ammonium chloride and sodium nitrite in equal
amount in a RB flask and fit the apparatus as shown in figure.
2. Heat the mixture with a Bunsen burner.
3. Heat initiates the chemical reaction between NH4Cl and NaNO2 and
nitrogen gas is produced. The evolved nitrogen gas passes through
delivery tube and gets collected in gas jar by the downward
displacement of water.

Precautions:
1. Ammonium chloride and sodium nitrite should not be used in the solid
form. They should be equimolar solutions in equal amounts.
2. The apparatus should be made air tight.
3. Heating should be uniform.

Tests of nitrogen gas

1. When a burning magnesium ribbon is introduced to the
mouth of gas jar containing nitrogen, it keeps on burning forming
yellow coloured ash. The yellow colour ash is magnesium nitride.
If some drops of water are put into the yellow coloured ash,
pungent smelling ammonia gets formed.

2. When a burning match stick is introduced to the mouth of a
gas jar containing nitrogen, it extinguishes. This proves that the
gas in the jar is nitrogen because nitrogen is neither combustible
nor the supporter of combustion.

Manufacture of nitrogen gas

1. From liquefied air

Air can be liquefied at a low temperature and high pressure.
After the air is liquefied, it is subjected to fractional distillation.
Nitrogen vapourizes faster than oxygen because the boiling
point of oxygen is -183°C and that of nitrogen is -196°C. The
escaped nitrogen gas is collected in the cylinder.

2. By removing CO2 and O2 from air
Carbon dioxide and oxygen of atmospheric air can be removed
together by shaking air with a solution of pyrogallol and caustic
soda. Pyrogallol absorbs oxygen and caustic soda absorbs CO2.
The left over nitrogen is then collected in a gas cylinder.

Properties of nitrogen gas

Physical properties:

211 Times' Crucial Science Book - 9

1. It is a colourless, odourless and tasteless gas.
2. It is insoluble in water.
3. It is neutral to litmus paper and other indicators.
4. It liquefies at -195°C and solidifies at -210°C.
5. It is neither combustible nor the supporter of combustion.

Chemical properties

Nitrogen does not react readily with other elements under ordinary
conditions. It is stable and inert. In nitrogen molecule, the two
nitrogen atoms are held together by a very strong triple bond. Since
high amount of energy is needed to dissociate this bond, nitrogen
is chemically inert. Due to this reason nitrogen is used to fill the
electric bulbs to provide inert atmosphere.

But nitrogen reacts with some elements in the presence of heat or
due to the use of heat and catalyst. Some chemical properties are:

1. Active metals such as magnesium and aluminium burn in the
atmosphere of nitrogen to form nitrides.

3Mg + N2 ∆ Mg3N2

Magnesium nitride

2Al + N2 ∆ 2AlN

Aluminium nitride

When nitride is treated with water, it gives corresponding
hydroxide and ammonia gas.

Mg3N2 + 6H2O ∆ 3Mg (OH)2 + 2NH3 ↑

Magnesium hydroxide

2. When a mixture of hydrogen and nitrogen in the ratio of 3:1
by volume is heated to about 450°C under the pressure of
200 - 600 atmosphere in the presence of finely divided iron as
catalyst and little metal oxide (MO) as promoter, ammonia gas
is produced. This process is known as Haber’s process. It is
used for the industrial production of ammonia.

N + 3H 2 NH450°C, 200-600 atm 3
2 2 Fe (catalyst), MO (promoter)

3. Nitrogen forms nitric oxide when it reacts with oxygen at very
high temperature of about 3000°C. This reaction also occurs
during lightning.

Times' Crucial Science Book - 9 212

N2 + O2 2000°C−3000°C 2NO
Nitric oxide

4. When nitrogen gas is passed through alumina in the presence
of coke at 900°C, aluminium nitride is formed.
Al2O3+ N2 + 3C 2000°C−3000°C 2AlN + 3CO

Aluminium nitride

Uses of nitrogen gas
1. Nitrogen gas is used in the production of ammonia, nitric acid, etc.
2. It is used to manufacture fertilizers.
3. Liquefied nitrogen is used as refrigerant to preserve food, fruits, fish,
meat etc.
4. Nitrogen gas is used in electrical bulb to provide inert atmosphere. If
oxygen gas is filled in the bulb, the bulb goes off immediately because
oxygen reacts with tungsten filament used in the bulb to form oxide.
5. It is used for making high temperature thermometers.

Learn and Write

1. Nitrogen gas is an inactive gas. Why?

Molecule of nitrogen gas is formed by the combination of two
atoms of nitrogen. These two atoms are held together by a very
strong triple bond. Since huge amount of energy is required
to break this bond, nitrogen does not takes part in chemical
reaction. Thus, the nitrogen is an inactive gas.

2. Nitrogen gas is used for replacing fuels in fuel tanks of
aeroplanes. Why?

Nitrogen gas being inactive gas prevents the formation of
explosive mixture of fuel and air. Therefore, it is used for
replacing fuels in fuel tanks of aeroplanes.

3. What is Haber's process? Write with balanced chemical
equation.

When a mixture of hydrogen and nitrogen in the ratio of 3:1
by volume is heated to about 450°C under the pressure of
200 - 600 atmosphere in the presence of finely divided iron as
catalyst and little metal oxide (MO) as promoter, ammonia gas
is produced. This process is known as Haber’s process.

N + 3H 2 NH450°C, 200-600 atm 3
2 2 Fe (catalyst), MO (promoter)

213 Times' Crucial Science Book - 9

Main points to remember

1. Nitrogen is an inactive gas which occupies 78% of the total volume of
atmosphere.

2. Nitrogen gas is prepared in the laboratory by heating ammonium
chloride and ammonium nitrite.

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

4. Nitrogen gas is a colourless, tasteless and odourless gas.
5. Nitrogen is neither combustible nor the supporter of combustion.
6. Nitrogen combines with hydrogen in the ratio of 1:3 in special conditions

to give ammonia.
7. Nitrogen is used to produce various types of chemicals.
8. Liquefied nitrogen is used as refrigerant to preserve foods, fruits, fish, meat, etc.
9. Nitrogen is filled in electric bulbs.

Exercise

1. Answer these questions in very short.
a. Write down the position of nitrogen gas in periodic table.
b. Name the thermometers in which nitrogen gas is used.

2. Answer these questions.
a. What are the general methods of preparation of nitrogen
gas? Write with balanced chemical equations.
b. Explain a method for the manufacture of nitrogen gas.
c. What are the physical properties of nitrogen gas?
d. What are the chemical properties of nitrogen gas? Write
with balanced chemical equations.
e. What are the uses of nitrogen gas?
f. How do you test nitrogen gas?
g. What do you understand by Haber’s process? What is its use?
h. Explain the laboratory preparation of nitrogen gas with a
labelled diagram.

3. Give reasons:
a. Nitrogen is filled in electric bulbs.
b. Nitrogen is chemically inert gas.
c. Nitrogen is collected in gas jar by the downward
displacement of water.

4. What happens when:
a. Sodium nitrate is heated with ammonium chloride.
b. Nitrogen and hydrogen are heated to 500°C under high
pressure.

Times' Crucial Science Book - 9 214

c. A burning magnesium ribbon is introduced to the gas jar
containing nitrogen.

d. Magnesium nitride is treated with water.
e. A mixture of nitrogen and oxygen is heated to 3000°C.
5. Diagrammatic questions:
a. Study the diagram given below and

answer the following questions:
i. What process is shown in the diagram?
ii. State the principle of the given process.
iii. Draw the diagram and label important
parts.

Project Work

Study the method of lab preparation of nitrogen given in the text and
arrange the apparatus. Then prepare nitrogen gas yourself and study its
properties.

215 Times' Crucial Science Book - 9

Chapter

12 Metals

Georgius Agricola

He is known as the pioneer in mineralogy.

Estimated Periods :3

Objectives

At the end of the lesson, students will be able to:
• explain the properties of metals;

• write the differences between metals and non-metals.

Mind Openers

• Can you give examples of metals?

• How can you differentiate between metals and non-metals? Discuss.

Introduction

The total number of elements discovered so far is 118. Most of these
elements are metals. Some are non-metals while a very few are
metalloids. In the modern periodic table, 79 elements are metals. The
metals have some special properties such as malleability, ductility,
conductivity, hardness, luster, sonorousness, etc. Mostly the metals
are found in nature in combined state in the form of minerals and
ores. Some of the inactive metals such as gold, platinum, mercury,
etc are found in free state also.

Occurrence of metals in Nepal

Metals occur in nature in the form of minerals and ores. Different
types of minerals and ores are found in different parts of Nepal. In
our country, more than 82 minerals and their varieties have been
identified in heavy concentration in different parts. The natural
occurrence of some of the metals is given below.

Iron

Magnetite and haematite are the important ores of iron. They are found in
Phulchoki (Lalitpur), Ramechhap, Janakpur, Tanahun, etc.

Copper

Chalcopyrite, azurite, copper bornite, etc are the ores of copper.

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These ores are found in Solukhumbu, Makwanpur, Dhading and
Udaypur districts.

Zinc

Zinc blende and calamine are the important ores of zinc. A large
deposit of zinc ores is found in Ganesh Himal, Rasuwa district.

Gold

Gold is found in free state in trace amounts in Swayambhu,
Halchowk area of Kathmandu. It is also found in trace amounts in
the banks of Bheri and Karnali rivers of Western Nepal.

Cobalt

Cobalt is found in traces in the form of cobaltite in Palpa district.

Calcium

It is found in the form of limestone. The limestone is found in
Chovar (Kath-mandu), Udaypur, Jogimara (Dhading), Chaukune
(Guthu, Surkhet), etc.

Metals are very useful to us. We use different metals such as iron,
aluminium, copper, silver, gold, platinum, etc. Iron and steel are
used for the construction of buildings, bridges, railway track,
machinery parts, roofs, pipes, weapons, household utensils, etc.
Aluminium is used for making coins, electric cables, household
utensils, etc. Similarly, gold, silver, etc are used in jewellery. The
metals such as titanium and zirconium are used in space missiles,
nuclear reactors, etc.

Properties of metals

Physical properties
1. Metals are solid at the ordinary temperature. Exception:

Mercury is in liquid state at ordinary temperature.
2. Metals are generally hard. The hardness varies from metal to

metal. Metals like lithium, sodium, etc are so soft that they
can be scratched with finger-nails. But steel is quite hard.
3. Metals are malleable in nature. Malleability means the
property of metals by which they can be beaten into thin sheet
by hammering.
4. Metals are ductile. Ductility is the property of metal due to
which it can be drawn into a thin wire.

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5. Metals have relatively high density but the density of lithium,
sodium and potassium is less than that of water.

6. Metals exhibit metallic luster when they are freshly cut or
wounded. Luster means the shining property of metal.

7. Metals are good conductors of heat and electricity.
8. Metals have high melting and boiling points. Some alkali

metals like lithium, sodium, potassium, etc have comparatively
low melting and boiling points.

Chemical properties:

1. Metals react with oxygen to form basic oxides.

4Na + O2 ∆ 2Na2O
2Mg + O2 ∆ MgO

2Fe + O2 → 2FeO

2. Active metals react with hydrogen to form corresponding
hydrides.

2Na + H2 → 2NaH
Sodium hydride

Ca + H2 → CaH2
Calcium hydride (Hydrolith)

3. Metals react with acids to give salt and hydrogen gas.

Zn + H2SO4 → ZnSO4 + H2↑
Mg + 2HCl → MgCl2 + H2↑
4. Metals form sulphide when heated with sulphur.

Fe + S → FeS

5. Metals react with halogens to form salts.

2Na + Cl2 → 2NaCl
2Fe + 3Cl2 → 2FeCl3
6. Some metals react with carbon to form carbides.

Ca + 2C → CaC2
Calcium carbide

7. More reactive metals replace less reactive metals from their
salts.

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Fe + CuSO4 → FeSO4 + Cu

Copper sulphate Iron sulphate
Non metals
Non metals are the electronegative elements, which do not conduct
heat and electricity and are not malleable, ductile, lustrous and
sonorous. Non-metals may be found in all three states, i.e, solid,
liquid and gas. Hydrogen, helium, carbon, oxygen, fluorine, sulphur,
phosphorus, iodine, etc are some non-metals.

Properties of non-metals

Physical properties
1. They may exist in either gas, solid or liquid form.

Gases : Hydrogen, helium, nitrogen, oxygen, fluorine, neon,
chlorine, argon, etc.
Liquid : Bromine.
Solid : Carbon, phosphorus, sulphur, iodine, etc.
2. They are soft and brittle, i.e. they break into pieces when
hammered. Exception: Diamond is a form of carbon but is
the hardest substance.
3. They are neither malleable nor ductile.
4. They do not have lusture.
Exception : Iodine and graphite are non-metals which
possess lustre.
5. They are the bad conductors of heat and electricity.
Exception: Graphite is a non-metal which is a good
conductor of electricity.
6. They are non-sonorous. They produce dull sound if struck.
7. They generally have low density.
8. They generally have low melting and boiling points.

Chemical properties

1. Non-metals form acidic oxides when heated with oxygen.
C + O2 → CO2
S + O2 → SO2

2. Non-metals react with halogens to form halide.

H2 + Cl2 → 2HCl

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P4 + 6I2 → 4PI3
3. More active non-metal displaces less active non-metal from
its aqueous solution.

2KI + Cl2 → 2KCl + I2
4. Non metals react with hydrogen to form stable hydrides.

N2 + 3H2 → 2NH3
S + H2 → H2S
H2 + Cl2 → 2HCl
Differences between metals and non-metals:

Metals Non-Metals

1. Metals are good conductors of 1. Non-metals are poor
heat and electricity. conductors of heat and
electricity. Exception:
graphite.

2. Metals are malleable. 2. Non-metals are not
malleable.

3. Metals are ductile. They can be 3. Non-metals are non-

drawn into wire. ductile. They are brittle.

4. Metals possess metallic lustre 4. Non-metals do not possess
when they are wounded or metallic lustre. Exception:
freshly cut. Exception: lithium. iodine and graphite.

5. Metals produce a peculiar 5. Non-metals do not produce

sound called metallic clink or sonorous sound. They

sonorous sound when struck with produce dull sound.

a hammer.

6. Metals have high melting and 6. Non-metals usually have

boiling point. low meltingand boiling point.

7. Metals are solid at ordinary 7. Non-metals are found in
temperature. Exception: mercury. any state, i.e. solid, liquid or

gas at ordinary temperature.

8. Metals are usually very hard 8. Non-metals are usually
in nature. soft in nature except
diamond. Diamond is the
hardest substance known.

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9. Metals cannot be easily broken 9. Non-metals can easily be

into pieces. broken into pieces.

10. Metals have high specific 10.Non-metals have low
gravity xcept ithium, sodium, specific gravityexcept
otassium and calcium. diamond.

11.Non-metals are lectronegative 11.Metals are electropositive

in nature, i.e., they gain electrons in nature, i.e., they lose

in chemical reactions. electrons in chemical

reaction.

12. Metals generally form basic 12. Non-metals generally
oxides except Cr2O3, Mn2O7 and form acidic oxides.
SnO2 etc. (Exception: CO, NO, H2O,
N2O, etc are neutral oxides).
13. Metals generally do not 13. Non-metals form stable
formhydrides but some metals hydrides with hydrogen.
form unstable hydrides NaH,
CaH2, etc. 14. Non-Metals generally do
14. Metals usually dissolve in not dissolve in acids.
acids forming salt and hydrogen
gas.

Metalloids

Elements which show the properties intermediate between metals and
non-metals are called metalloids. Arsenic, silicon, tellurium, antimony
and germanium are some examples of metalloids. Some of the common
properties of metalloids are as follows:
1. Metalloids are neither malleable nor ductile.
2. They are poor conductors of heat and electricity.
3. They possess metallic lustre.
4. They form alloys.
5. They exhibit allotropy. The property of an element to exist in

different physical forms is called allotropy.
6. Metalloids combine with hydrogen to form hydrides like AsH3

SbH3, etc.

Alloys

A homogeneous mixture of two or more metals or metals and non-
metals is called alloy. An alloy is formed by mixing metals or non-
metals in molten state. When the molten mixture is cooled slowly, a
hard and comparatively brittle mass is obtained. This mass can be

221 Times' Crucial Science Book - 9

used to make different equipments, appliances, etc.

Some common alloys and their composition are as follows:

SN Alloys Components

1. Steel Iron (99.75%) and Carbon (0.25%)

2. Brass Copper (70%) and Zinc (30%)

3. Bronze Copper (88%) and Tin (12%)

4. Nichrome Nickel (60%) and Chromium (40%)

Iron (80% - 86%), Chromium (12%),
5. Stainless steel

Nickel (1-8%), Carbon (0.25-2%)

6. Bell metal Copper (80%) and Tin (20%)

7. Solder Lead (50%) and Tin (50%)

Properties of alloys
1. Alloys are less malleable and ductile.
2. Alloy is harder and stronger than its individual components.
3. Usually, alloys are brittle in nature.
4. They are good conductors of heat and electricity.
5. They have low melting point.

Rusting
When a piece of iron comes in contact with moisture in the presence
of oxygen, it changes into reddish brown mass. This mass is called
rust and the process is called rusting. Thus, the process of formation
of brown layer on the surface of iron when it is exposed to moist air is
called rusting. Rusting of iron increases its weight but decreases the
strength. The chemical reaction of rusting can be shown as:

4Fe + 3O2 + xH2O →2Fe2O3.xH2O

rust

Iron can be prevented from rusting by covering with enamel,
galvanizing, turning into alloy, etc.
Role of Metals in Organisms
Different elements combine to form different living or non-living
molecules in our body. The major portion of our body (more than 95%)
is formed of non-metals. The principal non-metals that form our body
are carbon, hydrogen, nitrogen, phosphorus and sulphur. Metals are
also present in our body. The main metals that are present in our body
are sodium, potassium, calcium, zinc, magnesium, iron and copper.

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These metals are also present in the form of compounds. The living
molecules such as protein, nucleic acid, lipid, etc are formed form
these elements. These metals which are present in biological systems
are called biological inorganic elements.
The minerals or metal ions which are present in biological system
are also called nutrients. There are two kinds of nutrients-macro-
nutrients and micro-nutrients. The nutrients which are required in
the body in large quantity are called macro-nutrients. Na, Mg, K and
Ca are macro-nutrients. On the other hand, the nutrients which are
required in small quantities are called micro-nutrients. Mn, Fe, Cu,
Co, Zn, Mn, Mo etc are such nutrients.
Zinc in enzyme
Although zinc is a micro-nutrient, it is very important metal ion in our
body. It is present in a large number of enzymes in the body. About
300 enzymes in the human body contain zinc. It is found in almost
all organs of the body. It is found in cytoplasm, cells, tissues bones,
organs, etc. The total amount of zinc in the human body weighs about
2-3 grams. Out of this about 90% of zinc is found in muscles and bones.
Zinc is found in relatively large amount in the retina of eyes. The
concentration of zinc decreases gradually with age. Hence, the vision
power of eyes also decreases with age. Zinc is also found in prostrate
fluid and semen.

Zinc performs the following functions in the human body:
1. It is essential for the development of embryo in mother’s womb.

During infancy and childhood, the body needs zinc to grow and
develop properly.
2. It is needed for the sense of smell and taste.
3. It plays a role in cell division, cell growth, wound healing and
break down of carbohydrates.
4. Zinc helps to maintain immune system of the body against
diarrhoea, pneumonia and common cold.
5. It is needed to increase the fertility of men and menstrual cycle of women.
6. It is essential to treat anorexia (loss of appetite) in people.
7. It is also essential to treat psoriasis and neurodermatis.

Importance of sodium and potassium ions

Sodium and potassium metals are present in the form of ions in
human body. They are present inside and outside the cells. These
ions play very important role in the functioning of nervous system.

There is an interesting mechanism for the exchange of ions in cells.

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The sodium ions present outside the cell when enter into it, the
potassium ions leave the cell. This process occurs at the same time.
The process in which the sodium ions enter the cell and potassium
ions leave it at the same time is called sodium-potassium pump. The
sodium-potassium pump is essential for several processes in the
human body. It is essential to exchange information between neurons
and brain, to maintain the pH of electrolytes in the cell, to keep the
muscles healthy, to regulate the heart beat and body temperature,
etc.

Cell membrane

Na+ K+
Cytoplasm
Na+ Entry
Na+ K+

K+ Exit
K+

Sodium-potassium pump

Proper quantity of sodium and potassium ions and their optimum
regulation is essential for the body. Poor functioning of sodium-
potassium pump may result in muscular spasm, paralysis, migraine,
abnormal blood pressure, etc.

Harmful effects of mercury and lead in the body

Although some metals are crucial for the growth, development and
functioning of the human body, some metal ions have adverse effects
in human health. Mercury and lead are extremely harmful for the
human health.

Mercury

Mercury is extremely poisonous for the human body. Even a single
drop of mercury may block blood vessels and cause human body is
called hydrargyria or mercurialism. The compounds of mercury have
the following adverse effects in the human health:
1. The compounds of mercury damage the brain.
2. They also weaken the ability to speak, hear and see things.
3. They easily pass through placenta and adversely affect the growth

Times' Crucial Science Book - 9 224

and development of foetus.
4. They also damage affect kidney and lungs.
5. They adversely affect the development of brain of a child.

Lead

Lead is also a poisonous metal. It harms almost all organs of the
body. The compounds of lead have the following adverse effects in the
human health:
1. Lead mainly damages the human brain.
2. It can cause headache, abdominal pain, change in behaviour,

anaemia, etc in children.
3. It also hampers the development of brain in children.
4. Blood cannot combine with oxygen due to the presence of lead,

which causes anaemia.
5. Lead accumulated in bones hampers the formation of blood cells in

bone marrow.
6. It also affects the calcium absorption by bone which causes

weakening of bones.

Learn and Write

1. Cooking pots are made up of metals. Why?
Metals are good conductor of heat. When metals are used to make
cooking pots, the heat energy is supplied to the food through it
from the source of heat. Thus, the foods get cooked fast.

2. A moist iron piece left in the air becomes reddish brown. Why?
Moist iron reacts with oxygen to form hydrated iron oxide which
is reddish brown in colour. It is also called rust. Due to rusting, a
reddish brown colour is formed.
4Fe + 3O2 + xH2O →2Fe2O3.xH2O
rust

Main points to remember

1. Metals are malleable, ductile, electropositive and good conductors of
heat and electricity.

2. Elements which show the property intermediate between metal and
non-metals are called metalloids.

3. Non-metals are the electronegative elements which do not conduct heat
and electricity and are not malleable, ductile, lustrous and sonorous.

4. A homogeneous mixture of two or more metals or metals and non-
metals is called alloy.

5. The property by which metals can be beaten into thin sheets is called
malleability.

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6. The property of metals due to which they can be drawn into wire is
called ductility.

7. Graphite is a non-metal which is good conductor of electricity.

Exercise

1. Answer these questions in very short.
a. What is alloy? Give some examples.
b. What is rusting of iron?
c. Define:
i. Metals ii. Lustre iii.Ductibilit iv. Malleability
d. Name a liquid metal.

e. Name a liquid non-metal.
f. Can you give an example of non-metal that is a good

conductor of electricity?

2. Write down differences between:
a. Metals and non-metals. b. Metals and metalloids

3. Give reasons:
a. A piece of iron kept in moisture turns into reddish brown
after some days.

b. Alloys are preferred for construction work than the pure metals.

4. Write down the components of following alloys:

a. Brass b. Bronze c. Stainless steel

d. Solder e. Nichrome f. Steel

5. Answer these questions:
a. Write down the physical properties of metals.
b. What is alloy? Write its properties.
c. What are metalloids? Write their properties.
d. Write down the chemical properties of metals with balanced
chemical equations.

Project Work

Observe different things at your home and school. What things are made
of metals? For what purpose are they being used? Prepare a brief report.

Glossary
Minerals: naturally occurring substances which contain metals
Ores: the minerals from which metals can be extracted profitably
Cable: wire
Enzyme: a chemical substance that is produced by digestive glands

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Chapter

13 Carbon and
its Compounds
Richard Buckminister Fuller

Carbon molecules known as fullerenes were
named after his name due to his outstanding
contribution.

Estimated Periods :4

Objectives

At the end of the lesson, students will be able to:
• tell the sources of carbon;

• state physical and chemical properties of carbon;

• differentiate between organic and inorganic compounds.

Mind Openers

• Can you tell some substances which contain carbon?

• Can you tell some properties of carbon? Discuss.

Introduction

Symbol :C 6p
6n
Atomic number : 6

Atomic weight : 12 a.m.u

Valency :4

Position in the periodic table:Group IV A, Period: 2nd

Carbon is a non-metallic element which exists in a variety of forms.
The name carbon is derived from the Latin word carbo which means
charcoal or soot. It is the first element of sub-group IVA. Silicon,
germanium, tin, lead, etc are some other elements of the same
group.

Carbon is known to us since the ancient time. It is available
in different forms such as coal, charcoal, lamp black, graphite,
diamond, etc. The different forms of carbon are useful in daily life
in different ways such as charcoal and coal for heat, diamond for
jewellery and decoration, graphite as lubricant and pencil lead, etc.
Carbon is present in all living things. It is an important component

227 Times' Crucial Science Book - 9

of each cell of our body. It is also present in non-living things like
plastics, detergents, carbohydrates, drugs, furniture, firewood, etc.
Carbon is also present in gaseous state in combined form such as
carbon monoxide, carbon dioxide, etc.

Activity 13.1 To show that sugar contains carbon.

Materials required:

Burner, sugar, a spoon with a long stem, etc.

Procedure:

1. Put some sugar in a spoon.

2. Heat the spoon with burner at first slowly and then strongly.

Observation

Slow heating turns sugar into brown mass. The brown substance with good
smell formed on heating sugar is called caramel. If the caramel is further
heated strongly, it turns black. The black substance formed after heating
caramel is called charcoal, which is one of the forms of carbon.

Conclusion

The experiment shows that sugar contains carbon.

Sources of Carbon

Major sources of carbon are as follows:
1. Carbon is an essential constituent of all living organisms.
2. Carbon is present in all petroleum products and natural gases.
3. Carbon is the main component of carbon dioxide present in atmosphere.
4. It is also present in food materials such as carbohydrates, fat, protein, etc.
5. It is present in rocks and minerals such as limestone, bicarbonates, etc.
6. Carbon is present in firewood, coal, etc.

Nature of Carbon
Carbon is a non-metal with atomic number six. It consists of 2
electrons in K-shell and 4 electrons in L-shell. Due to the presence
of 4 electrons in valence shell, carbon needs to lose, gain or share
4 electrons to be in stable state. There are equal chance of losing
or taking of electrons to make the outermost orbit complete. But
energy considerations suggest that there is no possibility of taking
and losing of its electrons. Due to this, carbon forms covalent bond
with other elements by sharing electrons. For example, methane

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(CH4) is a carbon compound formed by sharing of electrons of a
carbon atom with four hydrogen atoms.

The number of electron pairs which an atom shares to acquire a
stable condition is called co-valency. Methane has four covalent
bonds of carbon with four atoms of hydrogen. So, carbon shows the
covalency four.

Catenation
The property of carbon due to which its atoms form a long chain
by combining with one another is called catenation. The number of
carbon compounds is very large due to the property of catenation
and co-valency of carbon. More than 5 millions of carbon compounds
have been discovered so far. A separate branch of chemistry studies
only carbon compounds because of its large number. The branch of
chemistry that deals with the compounds formed from carbon and
hydrogen is called organic chemistry. Some carbon compounds are:
methane, ethane, alcohol, glycerol, ether, etc.

HHH H H

H −C−C−C−C −C − H
HHH H H

Bonding between carbon atoms due to catenation
−−
−−
−−
−−
−−

Allotropy of carbon
Some elements exist in different physical forms with slightly different
chem-ical properties. Such forms of elements are called allotropes.
Thus, the property of an element to exist in different physical forms
with slightly different chemical properties is called allotropy. The
different physical forms of the elements are called allotropes. For
examples: diamond, graphite, coal, charcoal, lampblack, etc are
allotropes of carbon.

Allotropes of carbon can be categorized into two groups:
(i) Amorphous form: coal, charcoal, coke, lampblack, etc.
(ii) Crystalline form: diamond, graphite and fullerenes.

Diamond
Diamond is a crystalline allotrope of carbon. It is the purest form of
carbon. It is formed due to extremely high temperature and pressure
on pure coal inside earth’s surface. It is the hardest substance
known. All valence electrons of each carbon atom are used to form
bond. Therefore, there are no free electrons. Due to this, diamond is

229 Times' Crucial Science Book - 9

a bad conductor of heat and electricity.

Properties of diamond
1. Diamond is the hardest substance known.
2. It is the purest form of carbon.
3. It is a bad conductor of heat and electricity.
4. It has high refractive index, i.e. 2.24. So, it is used for decoration and
jewellery.
5. It has high melting point and density.

Uses of diamond
1. As it causes multiple reflection of light, it sparkles brightly. So, it is
used to make ornaments.
1. It is used for cutting and drilling metals, glass, etc.
1. It can be used to make radiation proof windows of spacecraft.

Graphite

Graphite is also a crystalline allotrope
of carbon. It is soft and greasy to touch.
It is also known as black lead. It is good
conductor of heat and electricity. It is due
to the fact that three valence electrons of
each carbon are used to make bond and
one electron is free in each carbon. The free
electrons are responsible for the conduction
of heat and electricity. The layer of graphite
is arranged in hexagonal shape with weak
force of attraction between the layers. Due
to weak bonding force, the layers of graphite easily slip one over
another. Though graphite is a non-metal; it possess metallic lustre.
It is insoluble in ordinary solvents.

Uses of graphite
1. It is used in manufacturing lead of pencils.

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1. It is used as electrode in electrolysis process.
1. It is used as dry lubricant.
1. It is used as a moderator in nuclear reactors.

Differences between diamond and graphite

Diamond Graphite

1. It is the hardest allotrope of carbon 1. It is the soft and slippery
allotrope of carbon.

2. It is a bad conductor of heat and2. It is a good conductor of heat

electricity. and electricity.

3. It does not have free electrons. 3. It consists of mobile electrons.

4. It is transparent and shining4. It is opaque and brown shining

crystalline solid. solid.

5. Its melting point is 3820°C. 5. Its melting point is 3670°C.

Fullerene
It is the newly discovered allotrope of carbon which occurs as
large symmetrical molecule. It was discovered in the year 1985
AD. It occurs in a number of forms. Carbon - 60 is the best known
fullerene. The molecule of carbon - 60 has the shape of a soccer ball.
Fullerene is expected to have a significant application in several
fields of chemistry.

Chemical properties of carbon

1. Carbon reduces metallic oxides of less reactive metals to their
corresponding metals on heating.
PbO + C → Pb + CO
CuO + C → Cu + CO
ZnO + C → Zn + CO

2. Carbon burns in oxygen to form carbon dioxide.
C + O2 → CO2

When the amount of oxygen is insufficient, carbon monoxide is
formed instead of carbon dioxide.

2C + O → 2CO (Carbon monoxide)
3. Carbon forms carbides on being heated with metals.

2C + Ca → CaC2 (Calcium carbide)

4Al + 3C → Al4C3

4. Carbon reacts with calcium oxide to give calcium carbide and

231 Times' Crucial Science Book - 9

carbon monoxide.
3C + CaO → CaC2 + CO
Calcium carbide

5. Carbon reacts with steam at a high temperature to produce
carbon monoxide and hydrogen.
C + H2O → CO + H2
Steam Water gas

The mixture of hydrogen and carbon monoxide gas is called water
gas. Water gas produces heat in excess amount on burning. Hence,
it is used as source of heat in industries.

Organic and inorganic compounds
1. Organic compounds

The compounds which contain carbon and hydrogen combined
together with other elements are called organic compounds. The
organic compounds which contain hydrogen and carbon only are
called hydrocarbons. Methane, ethane, propane, butane, alcohol,
ether, etc are some examples of organic compounds. The number
of organic compounds is much more than the number of inorganic
compounds.

2. Inorganic compounds

The compounds which are obtained from minerals are called
inorganic com-pounds. They do not contain carbon and hydrogen
bonded together. Water, common salt, sulphuric acid, nitric acid,
sodium hydroxide etc, are some examples of inorganic compounds.
Inorganic compounds are studied in inor-ganic chemistry. The
branch of chemistry which deals with the study of inor-ganic
compounds is called inorganic chemistry.

Differences between inorganic and organic compounds

Organic compounds Inorganic compounds

1. Organic compounds have direct 1. Inorganic compounds do not
carbon-carbon or carbon-hydrogen contain direct carbon-hydrogen
covalent bond. or carbon-carbon covalent bond.

2. They have covalent bonds. So, they 2. They have mostly

cannot ionize. electrovalent bonds. So, they can

ionize.

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3. They have low melting and boiling 3. Generally, they have high

point. melting and boiling point.

4. They mostly burn on heating because 4. Generally, they do not burn on

they contain carbon and hydrogen. heating.

5. They are usually insoluble in water. 5. Generally, they are soluble in
water.

6. These compounds are generally soluble 6. Generally, they are not soluble in
in organic solvents like ether, benzene, organic solvents.
etc.

Learn and Write

1. Graphite is a good conductor of electricity but not diamond. Why?
In graphite, only three valence electrons of each carbon are
used to make bond and one electron is left free. These electrons
are responsible for the conduction of electricity. But, all
electrons of each carbon are used to make bond in diamond.
Due to the absence of free electrons, diamond is bad conductor
of electricity.

2. Carbon forms covalent bond. Why?
Carbon atom has 4 electrons in the outermost orbit. Therefore,
it has equal chance of losing, gaining or sharing electrons to
make the outermost orbit completely filled. But the energy
considerations suggest that there is no possibility of gaining or
losing electrons. Due to this, carbon forms covalent bond with
other elements.

3. Graphite is used as a lubricant. Why?
The layer of graphite is arranged in hexagonal shape with weak
force of attraction between the layers. Due to weak bonding
force, layers of gra-phite easily slip one over another. Hence,
graphite is used as a lubricant.

Main points to remember

1. Carbon is a non-metallic element which can exist in different physical forms.
2. The property of carbon to form a long chain of its own atoms by joining

one atom to another is called catenation.
3. The property of an element to exist in different physical forms with

slightly different chemical properties is called allotropy.
4. Different physical forms of the same element are called allotropes.
5. Diamond is the hardest, transparent and purest form of carbon.
6. Graphite is a soft, opaque and good conductor of heat and electricity.

233 Times' Crucial Science Book - 9

7. The compounds which contain direct covalent bond between carbon
and hydrogen or carbon and carbon are called organic compounds.

8. The hydrocarbons and their derivatives are the organic compounds.
9. The branch of chemistry which deals with the study of organic

compounds is called organic chemistry.
10. The compounds which are obtained from minerals or inorganic sources

are called inorganic compounds.
11. The branch of chemistry which deals with the study of inorganic

compounds is called inorganic chemistry.

Exercise

1. Define:

a. Charcoal b. Caramel c. Catenation

d. Co-valency e. Hydrocarbons f. Organic chemistry

2. Answer these questions in short.

a. Explain the sources of carbon.

b. Write down the properties of graphite.

c. What do you understand by allotropy and allotropes?

d. What are the uses of graphite?

e. What are the chemical properties of carbon? Write with

balanced chemical equations.

f. What are organic and inorganic compounds? Give examples.

3. Write down differences between:
a. Organic and inorganic compounds
b. Diamond and graphite

4. Give reasons:
a. Graphite is used as a lubricant.
b. Carbon forms only covalent bonds.
c. Graphite is a good conductor of heat and electricity but
diamond is not.
d. Sugar turns into black mass on heating.

5. What happens when:
a. Carbon is heated with steam at high temperature?
b. Copper oxide is heated with carbon?
c. Carbon is heated with sufficient amount of oxygen?
d. Calcium reacts with carbon?
e. Carbon is heated with aluminium?

Times' Crucial Science Book - 9 234

Chapter

14 Water
Agnes Pockles
She is famous for introducing the
modern discipline known as surface
science, which describes the properties of
liquid and solid surfaces.

Estimated Periods :6

Objectives

At the end of the lesson, students will be able to:
• Describe the properties, sources and uses of water;
• Introduce the hardness of water and explain the methods of removing the

hardness of water with chemical reactions.

Introduction

Water is the most useful and most abundant substance on the earth.
Water is found in all three states, i.e. solid (ice), liquid (water) and
gas (vapour). Water is present everywhere on the surface of the earth
in different forms. It is available in the form of vapour, frost, clouds,
etc in air. More than two-thirds of the earth's surface is covered
by water. It occurs as snow on the high mountains. Similarly, it is
present in lake, well, river, ocean or sea as liquid on the surface of
the earth. Water is also present under the ground in its liquid form.
We can obtain underground water through well, tube well, spring,
deep boring, etc.

Out of the total water available on the earth, 97% water is present
in seas and oceans as salty water, which is useless for our daily use.
The remaining 3% is fresh water. The fresh water is the naturally
occurring water on Earth's surface in ice sheets, ice caps, glaciers,
icebergs, bogs, ponds, lakes, rivers and streams, and underground
as groundwater. Fresh water is characterized by having low
concentrations of dissolved salts. About 69 % of the fresh water
is found in the frozen state in glaciers and polar ice caps. The
underground water forms about 30 %. Only the 1% of fresh water
is available on the earth's surface and in the form of vapour in the
atmosphere. Hence, we suffer the scarcity of water in our daily life.

235 Times' Crucial Science Book - 9

Water is essential for the living of all organisms. The major portion
of the body weight of plants and animals is occupied by water. About
70% weight of the human body is composed of water. A ripe tomato
is composed of as much as 98% water! The water is essential for
several activities in our body. It is essential for digestion of food,
its absorption from intestine into the blood and transportation of
absorbed nutrients across the body. Water is also essential for the
excretion of wastes from the body. Water acts as a raw material
for the preparation of food by green plants by the process of
photosynthesis. Plants absorb minerals from soil through water
medium by their roots. The food prepared by the plants in leaves is
transported to all parts of plants in solution medium, i.e. with the
help of water.

Water flowing on the surface of earth is not pure. It contains some
dissolved or suspended impurities. The impurities bring changes in
the natural properties of water.

Physical properties of water

Water is the only substance on the surface of the earth to be
available in all three states, i.e. solid, liquid and gas. However, the
term water represents its liquid form. Pure water has following
physical properties:
1. Pure water is colourless, odourless and tasteless liquid.
2. It is a transparent liquid. It appears light blue in the deep ponds,

lakes, rivers, etc.
3. Pure water is a bad conductor of electricity. Water can conduct

heat by the process of convection.
4. Water is available in all three states, i.e. solid, liquid and gas.
5. Its melting point is 0°C and boiling point is 100°C. Water exists in

liquid form over wide range of temperature, i.e. from 0°C to 100°C.
6. Water is the best solvent for several solutes. It is also known as

universal solvent because it dissolves more substances than any
other solvent.

Times' Crucial Science Book - 9 236

7. Water has cohesive and adhesive properties. The cohesive and
adhesive properties of water help to conduct water from the roots
to the leaves through stem.
Water molecules are attracted to each other by a force of attraction
called hydrogen bond. This property of water is called cohesive
property. On the other hand, the water molecules stick to other
substances and make them wet. This is called adhesive property
of water.

8. Surface tension is another property of water. The property of
water due to which its surface resists the external force is called
surface tension. The surface tension is created at the surface of
the liquid due to cohesion between water molecules.

9. Water has a capacity to rise itself into a very fine capillary tube
without the aid of any external force. This property is called
capillary action of water.

10.When water is heated from 0°C to 4°C, its volume decreases and
density increases. Water has minimum volume and maximum
density at 4°C. This is called anomalous expansion of water.

Concave and convex meniscus

The shape of the liquid surface in which the sides are raised and
the middle is depressed is called concave meniscus. Water forms
a concave meniscus in a vessel. On the other hand, the shape of
the liquid surface in which the middle part is raised and the sides
are depressed is called convex meniscus. Mercury forms convex
meniscus.

Concave
meniscus

Water Concex
meniscus

Mercury

237 Times' Crucial Science Book - 9

Activity14 .1 To measure the volume of water

Materials required:

A measuring cylinder, water in a beaker, etc

Procedure:
1. Take a measuring cylinder of volume 100 ml capacity

and pour water up to half of it.
2. Observe the volume and the level of water carefully.

What kind of meniscus is it?
3. Focus your eyes at the lower meniscus of water and

find the volume of water in the measuring cylinder.

Observation:

You will see water level to be curved at the surface, i.e. the middle
portion of water is depressed more than the sides. This is called concave
meniscus.

Result:

The volume of water is ……………….. ml in the cylinder.

Conclusion:

We can measure the volume of water using a measuring cylinder. We
should focus our eyes at the lower meniscus while measuring the volume
of water.

Capillary action of water

As mentioned earlier, it is the property of water to rise up in a
narrow tube without any external force against the force of gravity.

Activity14 .2 To show the capillary action in a narrow glass tube.

Materials required:

A water trough or a beaker, a glass tube with fine bore, etc

Procedure:
1. Take a beaker or a water trough and fill half of it with

water.
2. Dip a narrow glass tube with very fine bore in the water

making it slanted on the side of the beaker.
3. Observe the level of water in the tube. Is the water level in the

tube below or above the surface of water in the beaker?

Times' Crucial Science Book - 9 238

Observation:

The level of water in the glass tube is higher than that in the beaker.

Conclusion:

The level of water rises up higher in the narrow glass tube than the
water level of the beaker due to capillary action of water.

Chemical properties

1. Water is a chemical compound containing two atoms of hydrogen
and one atom of oxygen in a molecule. It is represented as H2O.

2. Pure water is a neutral substance. It is neither acidic nor
basic. If an acid is added to water, it produces into hydronium
ion (H3O+) due to chemical reaction. Then water acts as an
electrolyte and conducts electricity.

H2O + HCl H3O+ + Cl-

Water Hydrochloric acid Hydronium ion Chloride ion

3. Water combines with ammonia gas to form ammonium
hydroxide.

Water + Ammonia → Ammonium hydroxide

H2O + NH3 → NH4OH
4. Water combines with sulphur trioxide to form sulphuric acid.

Water + Sulphur trioxide → Sulphuric acid

H2O + SO3 → H2SO4
5. Water reacts with carbon dioxide gas to form carbonic acid.

Water + Carbon dioxide → Carbonic acid

H2O + CO2 →H2CO3

6. Water reacts with alkali metals to form hydrogen gas and
metallic hydroxides.

2Li + H2O → 2 LiOH + H2

2K+ H2O → 2 KOH + H2

7. Water reacts with oxides, carbides and nitrides of some metals
to form metal hydroxides. Such reaction is called hydrolysis.

Mg3N2 + 6H2O → 3Mg(OH)2 + 2NH3

239 Times' Crucial Science Book - 9

8. If steam is passed over red hot iron, they react to produce
hydrogen gas.

Red hot iron + Steam → Ferroso-ferric oxide + Hydrogen

3Fe + 4H2O l Fe3O4 + 4H2↑

Solvent Property of Water
Water dissolves larger number of solutes than any other solvent.
So, water is regarded as a universal solvent. It is due to the polarity
(i.e. positive charge at one end and negative charge at other end) of
water molecule. In a water molecule, the oxygen atom withdraws
electrons more towards itself and gains a partial negative charge.
On the other hand, hydrogen atom gains a partial positive charge.
This makes the water molecule polar in nature.
A number of compounds such as Sodium chloride (NaCl), Calcium
chloride (CaCl2), Copper sulphate (CuSO4), Potassium nitrate
(KNO3), Silver nitrate (AgNO3), etc dissolve in water. Similarly,
acids, bases and salts dissolve in water. Some covalent compounds
such as sugar, glucose, alcohol, urea, HCl, also dissolve in water.
However, most organic and covalent compounds such as Carbon
tetrachloride (CCl4), Methane (CH4), Ethane, etc do not dissolve in
water.

Uses of Water

The uses of water can be categorized in to the following types:
1. Domestic use: Drinking, cooking, bathing, washing, cleaning,

etc are the domestic uses of water.
2. Industrial use: It is used to run factories. It is also used in

the extraction of metals, oil, and many other substances. It is
essential in laboratories to prepare solutions. It is essential for
fish farming. It is used for jet cutting. The process of cutting
wood, rubber, etc by passing water at very high pressure is
called jet cutting.
3. Entertainment use: Water is used to have entertainment such as
boating, rafting, swimming, water games, etc.
4. Generation of hydroelectricity: Water is essential for generating
hydroelectricity.
5. Uses for plants: We need water for the irrigation of our fields
and crops. Water supplies minerals salts and other nutrients
to the plants. The plants also need water to prepare food by the
process of photosynthesis.

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Soft and hard water

Water can be regarded as either soft or hard. It becomes hard due to
the presence of soluble salts of magnesium and calcium. These salts
reduce the capacity of water to form lather with soap. It means that
hardness decreases the lather forming or washing capacity of soap.

The water which contains the dissolved salts of magnesium and
calcium is called hard water. It destroys the soap because it
produces less lather with it. On the other hand, the water which
does not contain the dissolved salts of magnesium and calcium is
called soft water. Soft water produces enough lather with soap and
washes clothes well.

Activity14 .3 To identify the hard and soft water

Materials required:

A beaker, water from different sources, test tubes, a solution of soap or
shampoo, dropper, etc

Procedure:

1. Collect water from different sources
such as tap, well, tube well, stream,
etc and place them in separate test
tubes.

2. Prepare a solution of soap or
shampoo in a beaker.

3. Put five drops of soap solution in
each of the test tubes and shake
them carefully one by one.

4. Which water sample produces more
lather?

Observation:

No lather is obtained in some test tubes whereas good lather is seen in
other test tubes.

Conclusion:

The test tube, in which water easily forms lather with soap solution,
contains soft water. The test tubes in which water does not form lather
easily, contains hard water. Thus, we can identify hard and soft water.

241 Times' Crucial Science Book - 9

Types of hardness

On the basis of type of salt dissolved, the hardness of water can be
divided into two types. They are temporary hardness and permanent
hardness of water.

1. Temporary hardness

The hardness of water due to the dissolution of calcium bicarbonate or
magnesium bicarbonate in it is called temporary hardness of water.
The molecular formula of magnesium bicarbonate is Mg(HCO3)2
and that of calcium bicarbonate is Ca(HCO3)2. Such water is tasty
while drinking and makes our bones and teeth strong.

Removal of temporary hardness

The temporary hardness of water can easily be removed by boiling
or by the use of lime water.

a. Boiling: Boiling is the cheap and easy way to remove the
temporary hardness. Boiling decomposes the dissolved bicarbonates
into insoluble carbonates. The insoluble carbonates settle at the
bottom of the vessel and the hardness is removed.

Calcium bicarbonate → Calcium carbonate + Carbon dioxide +
Water

Ca(HCO3)2 → CaCO3↓ + CO2 + H2O
Magnesium bicarbonate → Magnesium carbonate + Carbon dioxide
+ Water

Mg(HCO3)2 → MgCO3↓ + CO2 + H2O
b. Use of lime water (Clark's Method): Lime water (calcium
hydroxide) reacts with the dissolved bicarbonates of hard water to
produce insoluble carbonates. The insoluble carbonates settle at the
bottom and the hardness is removed.

Calcium bicarbonate + Calcium hydroxide→ Calcium Carbonate +
Water

Ca(HCO3)2 + Ca(OH)2 → 2CaCO3↓ + 2H2O
Magnesium bicarbonate + Calcium hydroxide→ Magnesium
carbonate + Calcium carbonate + Water

Mg(HCO3)2 + Ca(OH)2 → MgCO3 + CaCO3↓ + 2H2O
Magnesium bicarbonate + Calcium hydroxide →Magnesium

Times' Crucial Science Book - 9 242

carbonat + Calcium carbonate + Water

Mg(HCO3)2 + Ca(OH)2 → MgCO3 + CaCO3 + 2H2O

Activity14 .4 To remove the temporary hardness of water by boiling

Materials required:

Beakers, test tubes, dropper, soap, water, calcium bicarbonate or magnesium
bicarbonate, etc

Procedure:

1. Take a beaker and fill about half of it with
water.

2. Add a spoonful of calcium bicarbonate or
magnesium bicarbonate to it
and stir it well using a stirrer or a spoon.

3. Prepare soap or shampoo solution in
another beaker.

4. Pour a little solution of calcium or
magnesium carbonate in a test tube
and add some drops of soap solution to it.

5. Shake the test tube well. Will you observe lather?

6. Boil the solution of magnesium or calcium carbonate for about 30
minutes, cool it and pour a little into a new test tube.

7. Add some drops of salt solution to this test tube and shake well. Will
you observe lather?

Observation:

You cannot see lather formation in the first case. But, you will observe good
lather in the second case.

Explanation:

No lather formation occurs in the first case because the water is hard due
to dissolved bicarbonate salt. When the solution is boiled, the bicarbonate
decomposes to give insoluble carbonate and the hardness is removed. Now,
the water is soft and good lather formation occurs.

Conclusion:

Temporary hardness of water can be removed by boiling.

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2. Permanent hardness

The hardness of water due to the dissolution of chlorides and
sulphates of calcium and magnesium is called permanent hardness.
The permanent hardness of water is caused by the following salts:

a. Magnesium chloride (MgCl2)
b. Magnesium sulphate (MgSO4)
c. Calcium chloride (CaCl2)
d. Calcium sulphate (CaSO4)
The permanent hardness of water cannot be removed by boiling. It
is removed by using washing soda or by Permutit process.

Removal of permanent hardness
The permanent hardness of water is removed by the use of washing
soda. The permanent hardness is removed in industrial scale by
permutit process.

a. Use of washing soda (Na2CO3.10H2O):
Washing soda reacts with the soluble salts of calcium and
magnesium and turns them into insoluble forms. This removes the
hardness and the water becomes soft. While removing the temporary
hardness, soluble salts NaCl and Na2SO4 are also produced as the
side products. However, they do not cause the hardness of water.

Calcium chloride + Sodium carbonate→Calcium carbonate +
Sodium chloride

CaCl2 + Na2CO3 → CaCO3↓ + 2NaCl
Calcium sulphate + Sodium carbonate → Calcium carbonate +
Sodium sulphate

CaSO4 + Na2CO3 → CaCO3 + Na2SO4
Similarly,
Megnesium chloride + Sodium carbonate → Magnesium carbonate
+ Sodium chloride

MgCl2 + Na2CO3 → MgCO3 + 2NaC1
Magnesium sulphate + Sodium carbonate → Magnesium carbonate
+ Sodium sulphate

MgSO4 + Na2CO3 → MgCO3 + Na2SO4
b. Use of Permutit process:
Permutit process is used to remove permanent hardness of water
in industrial scale. In this process, a complex compound called
sodium zeolite (permutit) is used to remove the hardness of water.
The molecular formula of sodium zeolite is Na2 (Al2SiO8) but is

Times' Crucial Science Book - 9 244

represented as Na2Z, in short form where Z stands for zeolite (Z =
Al2SiO8).
Principle:

Permutit process involves the replacement of magnesium and

calcium ions of hard water by sodium ions. Sodium permutit contains

enough replaceable sodium ions. When the hard water is passed

through the vessel packed with sodium permutit, the calcium and

magnesium ions present in the hard water combine with permutit

by replacing sodium ions. This makes hard water free from calcium

and magnesium ions and hence it is soft. The sodium ions that go

to water do not make it hard.

Sodium permutit removes the hardness as follows:

MgCl2 + Na2Z → MgZ + 2NaCl
MgSO4 + Na2Z → MgZ + 2Na2SO4
CaSO4 + Na2Z → CaZ + Na2SO4
CaCl2 + Na2Z → CaZ + 2NaCl
Sodium chloride and sodium sulphate formed in the reactions are

soluble in water because they do not cause hardness.

Process:

A special vessel known as Permutit

vessel is packed with a layer of coarse Hard water Brine
sand at the bottom. Over the sand, a

thick layer of sodium permutit is loaded.

The vessel is provided with two inlets Soft water

and two outlets. Hard water is supplied Zeolite

through one of the inlets. The other inlet Gravel
is for adding sodium chloride solution

as per requirement. The outlet that lies Permutit Process
near the bottom of the Permutit vessel

serves to remove waste water from the vessel. The other outlet lies

just above the Permutit layer, from where soft water is drained out.

When hard water is passed through the column of sodium permutit,

a chemical reaction takes place between sodium permutit and Ca++

or Mg++ ions present in the hard water. As a result the sodium ions

the permutit are replaced by calcium or magnesium ions. Now,

calcium and magnesium remain in the permutit whereas sodium

goes to water. This turns the hard water into soft.

If hard water is passed through the Permutit Vessel for a long

time, all the sodium permutit changes into calcium and magnesium

permutit. Then the hard water is no longer made soft. To regenerate

245 Times' Crucial Science Book - 9

sodium permutit in the vessel, a solution of sodium chloride is added
in the vessel. This restores sodium permutit in the vessel.

CaZ + 2 NaCl → Na2Z + CaCl2
MgZ + 2 NaCl → Na2Z + MgCl2
The waste water containing calcium and magnesium ions is removed
from the vessel through the bottom outlet.
Removal of both temporary and permanent hardness
If water contains both temporary and permanent hardness at the
same time, it is removed by treating with a mixture of washing
soda (Na2CO3) and caustic soda (NaOH). Caustic soda softens the
temporary hardness whereas washing soda softens permanent
hardness.
Mg(HCO3)2 + 2 NaOH → MgCO3 + Na2CO3 + 2 H2O
MgCl2 + Na2CO3 → CaCO3 + 2 NaCl

Activity14 .5 To remove the permanent hardness of water by washing soda

Materials required:

Magnesium chloride, beakers, test tubes, burner, tripod stand, spoon, etc

Procedure:

1. Take some water in a beaker.

2. Add a spoonful of magnesium chloride into it and stir it well.

3. Prepare a soap solution in another beaker.

4. Pour some solution of magnesium chloride in a test tube and drop some
drops of soap solution into it.

5. Shake the test tube well. Will you observe lather?

6. Now, add one spoonful of washing soda into the magnesium chloride
solution of beaker and stir well.

7. Take a little of solution obtained from step no. 6 in a test tube and add
some drops of soap solution.

8. Shake the mixture well. Will you observe lather?

Observation:

No lather is seen in the first case. However, a good lather formation occurs in
the second case.

Conclusion:

Permanent hardness can be removed by washing soda.

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