Class 9 Science_clone

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

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 molybelenum as a promoter.

N + 3H 2 NH ƒ& DWP 3
2 2 Fe (catalyst), Mo (promotor)

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,
C +2H2 ¨ CH4
Methane

S + H2 ¨ H2S

Uses of hydrogen
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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.

197 Times' Crucial Science Book - 9

,W UHGXFHV PHWDOOLF R[LGHV LQWR FRUUHVSRQGLQJ PHWDOV 6R LW LV
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
WKH WHPSHUDWXUH RI DERXW ƒ& 7KH ÁDPH ZKLFK LV
produced during the burning of hydrogen in oxygen is called
R[\ K\GURJHQ ÁDPH

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

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GLR[LGH LQHUW JDVHV ZDWHU YDSRXU HWF

2. Hydrogen is the lightest and simplest gas.
+\GURJHQ JDV LV REWDLQHG E\ WKH UHDFWLRQ RI PHWDOV ZLWK DFLGV
+\GURJHQ JDV LV SUHSDUHG LQ WKH ODERUDWRU\ E\ WKH DFWLRQ RI ]LQF ZLWK

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

ZDWHU
+\GURJHQ EXUQV ZLWK R[\JHQ WR SURGXFH ZDWHU
+\GURJHQ UHDFWV ZLWK QLWURJHQ DW ƒ& DQG ï DWPRVSKHUH

LQ WKH SUHVHQFH RI ÀQHO\ GLYLGHG LURQ ZLWK OLWWOH PRO\EGHQXP WR
produce ammonia.

Times' Crucial Science Book - 9 198

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
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) Hydrogenation
(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? HCl

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.

199 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 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.
3UHYLRXVO\ LW ZDV NQRZQ DV ÀUH JDV EHFDXVH LW LV QHFHVVDU\ IRU
EXUQLQJ /DYRLVLHU H[SHULPHQWDOO\ YHULÀHG WKDW LW FRQVWLWXWHV
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 + O2Ń
Mercuric oxide Mercury Oxygen

2Ag2O ¨ 4Ag + O2Ń
Silver oxide Silver Oxygen

2. From metallic peroxides

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

2Na2O2 + 2H22 ń 1D2+ 22Ń

Sodium peroxide Water Sodium hydroxide

Times' Crucial Science Book - 9 200

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 2H2Ń 22Ń

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 + 3O2Ń
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:

0L[ SRZGHUHG SRWDVVLXP FKORUDWH DQG PDQJDQHVH GLR[LGH LQ WKH UDWLR
RI E\ ZHLJKW

3ODFH WKH PL[WXUH LQ WKH KDUG JODVV WHVW WXEH DQG ÀW WKH DSSDUDWXV DV
VKRZQ LQ ÀJXUH

Hard glass test tube

Mixture of Delivery tube Oxygen gas
MnO2 + KClO3 Gas jar

Burner Trough
Water

Laboratory preparation of oxygen gas

201 Times' Crucial Science Book - 9

+HDW WKH PL[WXUH ZLWK WKH %XQVHQ EXUQHU 1RZ SRWDVVLXP FKORUDWH
dissociates to produce potassium chloride and oxygen. The oxygen gas
passes through delivery tube to the gas jar and gets collected in the gas
MDU E\ WKH GRZQZDUG GLVSODFHPHQW RI ZDWHU

Precautions
1. Manganese dioxide (catalyst) should be used in pure form. If impure
manganese dioxide is used, the carbon particles present in manganese
GLR[LGH PD\ EXUQ DQG H[SORVLRQ PD\ WDNH SODFH
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 + O2Ń

Apparatus required:

&RQLFDO ÁDVN WKLVWOH IXQQHO GHOLYHU\ WXEH ZDWHU WURXJK EHHKLYH
shelf, gas jar, cork, etc.

Chemicals required:

1. Hydrogen peroxide ((HM2nOO2)2)
2. Manganese dioxide
3. Water (H2O)

Hydrogen peroxide

Funnel with a stopper

Oxygen gas

Delivery Gas jar
tube
&RQLFDO ÁDVN

Water
Beehive shelf

Laboratory preparation of oxygen gas

Times' Crucial Science Book - 9 202

Procedure:
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2. Pour hydrogen peroxide through a funnel having a stopper to the mix-
WXUH RI PDQJDQHVH GLR[LGH DQG ZDWHU
3. Hydrogen peroxide decomposes to give oxygen as it comes in contact
ZDQLWGK J 0HWVQ 2FR2O.OHTFhWHuGs LpQr oWKdHu JceDdV oMDxUy Eg\en GRpZasQsZesDtUhGr oGuLVgShODtFhHePdHeQliWv ReIr yZtDuWHbUe

Fact Reason

Why is oxygen collected in gas jar by downward displacement
of water?
Oxygen is slightly soluble in water and is lighter than air. Hence,
oxygen is collected in gas jar by downward displacement of water.

Test of Oxygen

Take a burning matchstick to the mouth of the gas jar containing
WKH JDV ,I WKH PDWFKVWLFN FRQWLQXHV EXUQLQJ ZLWK EULJKWHU ÁDPH
the gas in the gas jar is oxygen. It is the only gas which supports
burning but doesn’t burn itself.

Fact Reason

Why does burning matchstick burn more brightly when inserted
to the gas jar of oxygen?
The burning matchstick burns more brightly when inserted to
the gas jar of oxygen because oxygen supports combustion.

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
QLWURJHQ LV ï ƒ& DQG WKDW RI R[\JHQ LV ï ƒ& :KHQ OLTXLG DLU LV
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
RI ZDWHU :KHQ HOHFWULFLW\ LV SDVVHG WKURXJK DFLGLÀHG ZDWHU LW
decomposes water into hydrogen and oxygen.

2H2O electrolysis 2H2 + O2

203 Times' Crucial Science Book - 9

Properties of oxygen

Physical properties
1. It is a colourless, odourless and tasteless gas.
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GLVVROYHG LQ ZDWHU
3. It is neutral to litmus paper.
4. It is slightly heavier than air.
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Chemical properties

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

4P + 5O2 ¨ 2P2O5
Phosphorus pentoxide

S + O2 ¨ SO2
Sulphur dioxide

Times' Crucial Science Book - 9 204

4. When iron is strongly heated with oxygen, ferroso-ferric oxide
is produced.

3Fe + 2O2 ¨ Fe3O4
Ferroso - ferric oxide

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produce nitrogen and water vapour.

4NH3 + 3O2 ń +2O + 2N2Ń

6. Hydrocarbons burn with oxygen to produce CO2, water vapour
and heat energy.

CH4 + 2O2 ¨ CO2 + 2H2O + heat
7. When glucose present in cells of our body burns with oxygen, it

produces carbon dioxide, water vapour and energy.

C6H12O6 + 6O2 ń &22 + 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.
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/LTXHÀHG R[\JHQ LV XVHG LQ URFNHW DV D SDUW RI IXHO
4. The burning of oxygen and acetylene gas produces large amount of
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GXH WR WKH EXUQLQJ RI DFHW\OHQH ZLWK R[\JHQ LV FDOOHG R[\DFHW\OHQH ÁDPH
0LQH ZRUNHUV VHD GLYHUV DQG PRXQWDLQHHUV FDUU\ R[\JHQ F\OLQGHUV IRU
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?
lMraebaacnptgiroaennpeathsreaetrdieoibnoyxoiidnfecorx(eMyagsneinOng2g)tahwse.orrMaktsneOaos2f a positive catalyst during the
increases the rate of chemical
production of oxygen gas.

205 Times' Crucial Science Book - 9

Main points to remember

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2. Oxygen gas is prepared by heating metallic peroxides, metallic oxides,

HOHFWURO\VLV RI ZDWHU HWF
3. Oxygen gas is prepared in the laboratory by heating potassium

chlorate in the presence of manganese dioxide.
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5. Oxygen is used by all living things for respiration.
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XVHG IRU ZHOGLQJ PHWDOV
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?
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: H2O2
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.

Times' Crucial Science Book - 9 206

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.

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.

207 Times' Crucial Science Book - 9

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 + N2Ń

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

8NH3 + 3Cl2 ń 1+4Cl + N2Ń
3. From ammonium dichromate

Nitrogen gas can be obtained by heating ammonium dichromate.

(NH4)2Cr2O7 ń12 + Cr2O3 + 4H2O

4. By passing air through heated copper

wAihricfrheecdomfrboimneCsOw2 iatnhdomxyogisetnuroef is passed over heated copper
air to form oxide. But the
nitrogen is left unreacted. The left nitrogen can be collected by
downward displacement of water.

2Cu + (O2, N2 ń &X2 12
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 + N2Ń

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

NaNO2 + NH4&O ń 1+4NO2 + NaCl
NH4NO2 ń +2O + N2Ń

Times' Crucial Science Book - 9 208

Apparatus required:

%XQVHQ EXUQHU VWDQG ZLUH JDXJH WULSRG VWDQG URXQG ERWWRP ÁDVN
cork, delivery tube, beehive shelf, water trough, gas jar, etc.

Chemicals required:
1. ASWomadtmieuromn(Hinu2iOmtr)icthel(oNriadNe O(N2)H4Cl)
2.
3.

Stand Thistle funnel
Delivery tube

5RXQG ERWWRP ÁDVN Wire Nitrogen gas
Solution of ammonium gauge
chloride and sodium nitrite Gas jar
Burner
Tripod stand Lab preparation of nitrogen gas Trough
Water
Bee-hive shelf

Procedure:

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DPRXQW LQ D 5% ÁDVN DQG ÀW WKH DSSDUDWXV DV VKRZQ LQ ÀJXUH
+HDW WKH PL[WXUH ZLWK D %XQVHQ EXUQHU
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nitrogen gas is produced. The
WXEH DQG JHWV FROOHFWHG LQ JDV MDU E\ WKH GRZQZDUG GLVSODFHPHQW RI ZDWHU

Precautions:
1. Ammonium chloride and sodium nitrite should not be used in the solid
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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.

209 Times' Crucial Science Book - 9

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

)URP OLTXHÀHG DLU

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$IWHU WKH DLU LV OLTXHÀHG LW LV VXEMHFWHG WR IUDFWLRQDO GLVWLOODWLRQ
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:
1. It is a colourless, odourless and tasteless gas.
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3. It is neutral to litmus paper and other indicators.
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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
LV FKHPLFDOO\ LQHUW 'XH WR WKLV UHDVRQ QLWURJHQ LV XVHG WR ÀOO WKH
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:

Fact Reason

Why is nitrogen less reactive?
Nitrogen molecule is formed by triple covalent bonds between two
QLWURJHQ DWRPV ZKLFK LV YHU\ GLIÀFXOW WR EUHDN GXULQJ FKHPLFDO
reaction. So, nitrogen is less reactive.

Times' Crucial Science Book - 9 210

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 Ń
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
DWPRVSKHUH LQ WKH SUHVHQFH RI ÀQHO\ GLYLGHG iron as
catalyst and little Molybdenum (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 NH ƒ& DWP 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.

N2 + O2 ƒ&ï ƒ& 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 ƒ&ï ƒ& 2AlN + 3CO
Aluminium nitride

Uses of nitrogen gas
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meat etc.
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,W LV XVHG IRU PDNLQJ KLJK WHPSHUDWXUH WKHUPRPHWHUV

211 Times' Crucial Science Book - 9

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 take 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
DWPRVSKHUH LQ WKH SUHVHQFH RI ÀQHO\ GLYLGHG LURQ DV
catalyst and Molybdenum (Mo) as promoter, ammonia gas is
produced. This process is known as Haber’s process.

N2 + 3H2 ƒ& DWP 2 NH3
Fe (catalyst), Mo (promoter)

Main points to remember

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atmosphere.

1LWURJHQ JDV LV SUHSDUHG LQ WKH ODERUDWRU\ E\ KHDWLQJ DPPRQLXP
chloride and ammonium nitrite.

1LWURJHQ JDV LV FROOHFWHG LQ WKH JDV MDU E\ WKH GRZQZDUG GLVSODFHPHQW
RI ZDWHU

1LWURJHQ JDV LV D FRORXUOHVV WDVWHOHVV DQG RGRXUOHVV JDV
1LWURJHQ LV QHLWKHU FRPEXVWLEOH QRU WKH VXSSRUWHU RI FRPEXVWLRQ
1LWURJHQ FRPELQHV ZLWK K\GURJHQ LQ WKH UDWLR RI LQ VSHFLDO FRQGLWLRQV

to give ammonia.
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/LTXHÀHG QLWURJHQ LV XVHG DV UHIULJHUDQW WR SUHVHUYH IRRGV IUXLWV ÀVK PHDW HWF
1LWURJHQ LV ÀOOHG LQ HOHFWULF EXOEV

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.

Times' Crucial Science Book - 9 212

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.
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. NH4Cl
+
iii. Draw the diagram and label
NaNO2

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.

213 Times' Crucial Science Book - 9

Chapter

12 0HWDOV

Georgius Agricola

He is known as the pioneer in mineralogy.

ƐƟŵĂƚĞĚ WĞƌŝŽĚƐ ͗ ϯ

Objectives

ƚ ƚŚĞ ĞŶĚ ŽĨ ƚŚĞ ůĞƐƐŽŶ͕ ƐƚƵĚĞŶƚƐ ǁŝůů ďĞ ĂďůĞ ƚŽ͗
• H[SODLQ WKH SURSHUWLHV RI PHWDOV
• 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
LGHQWLÀHG LQ KHDY\ 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.

Times' Crucial Science Book - 9 214

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 ZLWK ÀQJHU QDLOV %XW VWHHO LV TXLWH KDUG
3. Metals are malleable in nature. Malleability means the
property of metals by which they can be beaten into thin sheet
by hammering.

215 Times' Crucial Science Book - 9

4. Metals are ductile. Ductility is the property of metal due to
which it can be drawn into a thin wire.

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 ¨ 2MgO

2Fe + O2 ń )H2

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

2Na + H2 ń S1odDi+um hydride

Ca + H2 ń &CDa+lc2ium hydride (Hydrolith)

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

Zn + H2SO4 ń =Q624 + H2Ń
0J +&O ń 0J&O2 + H2Ń
4. Metals form sulphide when heated with sulphur.

)H 6 ń )H6

5. Metals react with halogens to form salts.

2Na + Cl2 ń 1D&O
2Fe + 3Cl2 ń )H&O3
6. Some metals react with carbon to form carbides.

&D & ń C&aDl&ci2um carbide

Times' Crucial Science Book - 9 216

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

Fe + CuSO4 Cńop per)sHu6l2ph4 ate+ Cu
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,
OLTXLG DQG JDV +\GURJHQ KHOLXP FDUERQ R[\JHQ ÁXRULQH VXOSKXU
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 : +\GURJHQ KHOLXP QLWURJHQ R[\JHQ ÁXRULQH QHRQ
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.

Fact Reason

Why are iron and coppers used to make wires?
Iron and coppers are malleable, ductile and good conductor of
electricity. Hence, they are used to make wires.

217 Times' Crucial Science Book - 9

Chemical properties

1. Non-metals form acidic oxides when heated with oxygen.
C + O2 ń &22
S + O2 ń 622

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

H2 + Cl2 ń +&O
4P + 6I2 ń 3,3
3. More active non-metal displaces less active non-metal from
its aqueous solution.

2KI + Cl2 ń .&O ,2
4. Non metals react with hydrogen to form stable hydrides.

N2 + 3H2 ń 1+3
S + H2 ń +2S
H2 + Cl2 ń +&O
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 3. Non-metals are non-
be drawn into wire. ductile. They are brittle.

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

5. Metals produce a peculiar 5. Non-metals do not
sound called metallic clink or produce sonorous sound.
sonorous sound when struck They produce dull sound.
with a hammer.

Times' Crucial Science Book - 9 218

6. Metals have high melting and 6. Non-metals usually have
boiling point. low melting and boiling
point.
7. Metals are solid at ordinary
temperature. Exception: 7. Non-metals are found
mercury. in any state, i.e. solid,
liquid or gas at ordinary
8. Metals are usually very hard temperature.
in nature.
8. Non-metals are usually
9. Metals cannot be easily soft in nature except
broken into pieces. diamond. Diamond is the
hardest substance known.
0HWDOV KDYH KLJK VSHFLÀF
gravity except lithium, 9. Non-metals can easily be
sodium, potassium and broken into pieces.
calcium.
10. Non-metals have low
11. Non-metals are elctronegative VSHFLÀF JUDYLW\ H[FHSW
in nature, i.e., they gain diamond.
electrons in chemical
reactions. 11. Metals are electropositive
in nature, i.e., they lose
12. Metals generally form basic electrons in chemical
oxides except Cr2O3, Mn2O7 reaction.
and SnO2 etc.
12. Non-metals generally form
13. Metals generally do not form acidic oxides. (Exception:
hydrides but some metals CneOu,tNraOl ,oHxi2dOe,s)N. 2O, etc are
form unstable hydrides NaH,
CaH2, etc. 13. Non-metals form stable
hydrides with hydrogen.
14. Metals usually dissolve
in acids forming salt and 14. Non-metals generally do
hydrogen gas. not dissolve in acids.

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.

219 Times' Crucial Science Book - 9

2. They are poor conductors of heat and electricity.
3. They possess metallic lustre.
4. They form alloys.
7KH\ H[KLELW DOORWURS\ 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
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%)

5. Stainless steel Iron (80% - 86%), Chromium (12%),
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.
7KH\ KDYH ORZ PHOWLQJ SRLQW
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

Times' Crucial Science Book - 9 220

the strength. The chemical reaction of rusting can be shown as:
4Fe + 3O2 + xH22 ń )H2O3.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. 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
SURVWUDWH ÁXLG and semen.

221 Times' Crucial Science Book - 9

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.
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.

Fact Reason

Zinc is very essential for reproductive health.
Zinc helps to boost the immunity, increase fertility in males and
regulate menstrual cycle in female. Hence, zinc is very essential
for reproductive health.

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.
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 Cell membrane

information between K+

neurons and brain, to Na+ Cytoplasm
maintain the pH of K+

electrolytes in the cell, to Na+ Entry K+ Exit
keep the muscles healthy, Na+ K+

to regulate the heart beat
and body temperature,
etc.

Sodium-potassium pump

Times' Crucial Science Book - 9 222

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 hydrargyria or
mercurialism in human body. 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

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

Fact Reason

We should avoid mercury, why?
Intake of mercury has adverse effects on health. It damages brain,
affects the senses and even harms the development of the foetus.
So, we should avoid mercury.

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.
Lead accumulated in bones hampers the formation of blood cells in

bone marrow.

223 Times' Crucial Science Book - 9

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 + xH22 ń )Hr2uOs3t.xH2O

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

Main points to remember

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

(OHPHQWV ZKLFK VKRZ WKH SURSHUW\ LQWHUPHGLDWH EHWZHHQ PHWDO DQG
non-metals are called metalloids.

1RQ PHWDOV DUH WKH HOHFWURQHJDWLYH HOHPHQWV ZKLFK GR QRW FRQGXFW KHDW
and electricity and are not malleable, ductile, lustrous and sonorous.

$ KRPRJHQHRXV PL[WXUH RI WZR RU PRUH PHWDOV RU PHWDOV DQG QRQ
metals is called alloy.

7KH SURSHUW\ E\ ZKLFK PHWDOV FDQ EH EHDWHQ LQWR WKLQ VKHHWV LV FDOOHG
malleability.

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called ductility.

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Times' Crucial Science Book - 9 224

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.Ductility 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.

225 Times' Crucial Science Book - 9

Chapter

13 &DUERQ DQG LWV
&RPSRXQGV

Richard Buckminister Fuller

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

Objectives ƐƟŵĂƚĞĚ WĞƌŝŽĚƐ ͗ϰ

ƚ ƚŚĞ ĞŶĚ ŽĨ ƚŚĞ ůĞƐƐŽŶ͕ ƐƚƵĚĞŶƚƐ ǁŝůů ďĞ ĂďůĞ ƚŽ͗

• WHOO WKH VRXUFHV RI FDUERQ
• VWDWH SK\VLFDO DQG FKHPLFDO SURSHUWLHV RI FDUERQ
• 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 ,W LV WKH ÀUVW HOHPHQW RI VXE JURXS ,9$ 6LOLFRQ
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

Times' Crucial Science Book - 9 226

of each cell of our body. It is also present in non-living things like
plastics, detergents, carbohydrates GUXJV IXUQLWXUH ÀUHZRRG HWF
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.
+HDW WKH VSRRQ ZLWK EXUQHU DW ÀUVW VORZO\ DQG WKHQ VWURQJO\
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.
,W LV SUHVHQW LQ URFNV DQG PLQHUDOV VXFK DV OLPHVWRQH ELFDUERQDWHV HWF
&DUERQ LV SUHVHQW LQ ÀUHZRRG FRDO HWF

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

227 Times' Crucial Science Book - 9

(cCarHb4o)nisataomcawrbitohnfocuomr hpyodurnodgefnoramtoemd sb.y sharing of electrons of aïï
The number of electron pairs which an atom shares to acquire aïï
stable condition is called co-valency. Methane has four covalentïï
bonds of carbon with four atoms of hydrogen. So, carbon shows theïï
covalency four. ïï
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 ïCïCïCïC ïC ï H

HHH H H
Bonding between carbon atoms due to catenation

Allotropy of carbon
Some elements exist in different physical forms with slightly different
chemical 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
example: 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.

Allotropes of carbon

Crystalline Amorphous

Diamond Graphite Fullerenes Coal Charcoal Lamp black

Times' Crucial Science Book - 9 228

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
a bad conductor of heat and electricity.

Properties of diamond
1. 'LDPRQG LV WKH KDUGHVW VXEVWDQFH NQRZQ
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
MHZHOOHU\
5. It has high melting point and density.

Uses of diamond
1. $V LW FDXVHV PXOWLSOH UHÁHFWLRQ RI OLJKW LW VSDUNOHV EULJKWO\ 6R LW LV
XVHG WR PDNH RUQDPHQWV
1. It is used for cutting and drilling metals, glass, etc.
1. ,W FDQ EH XVHG WR PDNH UDGLDWLRQ SURRI ZLQGRZV RI VSDFHFUDIW.

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.

229 Times' Crucial Science Book - 9

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

Fact Reason

Graphite is good conductor though it is non metal, why?
Graphite is good conductor though it is non metal because it has
free electrons.

Differences between diamond and graphite

Diamond Graphite

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

2. It is a bad conductor of heat and 2. 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 shining 4. It is opaque and brown
crystalline solid.
shining 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
H[SHFWHG WR KDYH D VLJQLÀFDQW DSSOLFDWLRQ LQ VHYHUDO ÀHOGV RI FKHPLVWU\

Chemical properties of carbon

1. Carbon reduces metallic oxides of less reactive metals to their
corresponding metals on heating.
3E2 & ń 3E &2

&X2 & ń &X &2
=Q2 & ń =Q &2
2. Carbon burns in oxygen to form carbon dioxide.
:KHQ WKHC D+PORX2 QńW R&I 2R[2 \JHQ LV LQVXIÀFLHQW FDUERQ PRQR[LGH LV

formed instead of carbon dioxide.
& 2 ń &2 &DUERQ PRQR[LGH

Times' Crucial Science Book - 9 230

3. Carbon forms carbides on being heated with metals.
& &D ń &D&2 (Calcium carbide)

$O & ń $O4C3
4. Carbon reacts with calcium oxide to give calcium carbide and

carbon monoxide.
& &CD2al cńiu &mDc&a2r+biCdeO

5. Carbon reacts with steam at a high temperature to produce
carbon monoxide and hydrogen.
C +SHte22am ń &W2a t e r+g2as

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.

231 Times' Crucial Science Book - 9

2. They have covalent bonds. So, they 2. They have mostly electrovalent
cannot ionize. bonds. So, they can ionize.

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 6. Generally, they are not soluble
soluble in organic solvents like ether, in organic solvents.
benzene, 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
PDNH WKH RXWHUPRVW RUELW FRPSOHWHO\ ÀOOHG %XW WKH HQHUJ\
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 graphite easily slip one over another. Hence,
graphite is used as a lubricant.

Main points to remember
&DUERQ LV D QRQ PHWDOOLF HOHPHQW ZKLFK FDQ H[LVW LQ GLIIHUHQW SK\VLFDO IRUPV
7KH SURSHUW\ RI FDUERQ WR IRUP D ORQJ FKDLQ RI LWV RZQ DWRPV E\ MRLQLQJ

one atom to another is called catenation.
7KH SURSHUW\ RI DQ HOHPHQW WR H[LVW LQ GLIIHUHQW SK\VLFDO IRUPV ZLWK

slightly different chemical properties is called allotropy.
4. Different physical forms of the same element are called allotropes.

Times' Crucial Science Book - 9 232

5. Diamond is the hardest, transparent and purest form of carbon.
*UDSKLWH LV D VRIW RSDTXH DQG JRRG FRQGXFWRU RI KHDW DQG HOHFWULFLW\
7KH FRPSRXQGV ZKLFK FRQWDLQ GLUHFW FRYDOHQW ERQG EHWZHHQ FDUERQ

and hydrogen or carbon and carbon are called organic compounds.
8. The hydrocarbons and their derivatives are the organic compounds.
7KH EUDQFK RI FKHPLVWU\ ZKLFK GHDOV ZLWK WKH VWXG\ RI RUJDQLF

compounds is called organic chemistry.
7KH FRPSRXQGV ZKLFK DUH REWDLQHG IURP PLQHUDOV RU LQRUJDQLF VRXUFHV

are called inorganic compounds.
7KH EUDQFK RI FKHPLVWU\ ZKLFK GHDOV ZLWK WKH VWXG\ RI LQRUJDQLF

compounds is called inorganic chemistry.

Exercise

1. Define: c. Catenation
a. Charcoal b. Caramel
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?

233 Times' Crucial Science Book - 9

Chapter

14 :DWHU

Agnes Pockles

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

ƐƟŵĂƚĞĚ WĞƌŝŽĚƐ ͗ ϲ

Objectives

ƚ ƚŚĞ ĞŶĚ ŽĨ ƚŚĞ ůĞƐƐŽŶ͕ ƐƚƵĚĞŶƚƐ ǁŝůů ďĞ ĂďůĞ ƚŽ͗
• ' HVFULEH WKH SURSHUWLHV VRXUFHV DQG XVHV RI ZDWHU
• 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 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.

Times' Crucial Science Book - 9 234

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.

:DWHU ÁRZLQJ RQ WKH VXUIDFH RI HDUWK LV QRW SXUH ,W FRQWDLQV VRPH
dissolved or suspended impurities. The impurities bring changes in
the natural properties of water.

Sources of water

We need water for bathing, cooking, sea
washing, cleaning, irrigating, drinking,
recreating, etc. We get required water
from various sources. The sources from
which we get water are called sources of
water.

The sources of water are broadly categorized into two categories.
They are: surface water and underground water.

Surface water

The sources of water which are found on the surface of the earth are
called surface water. Following are some examples of surface water:

1) Sea or ocean: Ocean or sea is the largest source of water.
97% of total water is found in the ocean or sea. Such water

235 Times' Crucial Science Book - 9

dissolves large amount of salt. Therefore, this water is not
suitable for drinking and irrigation. This water is suitable for
transportation and hydroelectricity generation.
2) Rivers, lakes and ponds: Rivers, lakes and ponds are other
sources of surface water. Some rivers originate from melting
of snow from mountains whereas some rivers are formed from
rain water. Most of the lakes are formed from melting of ice
whereas some lakes and ponds are formed form rainwater,
water run- off from adjacent land and from streams. The
water obtained from these sources are useful for human
beings. Human beings use water obtained from these sources
for drinking, cooking, bathing, cleaning, irrigation, running
factories, generating hydroelectricity, etc.

Lake Pond River

3) Glaciers: Glacier is solid Glacial lake
form of water found in
Himalayas. Glacial lake
is formed when glacier
melts. Glacial water is
the largest source of fresh
water on the earth surface.

4) Rain: Rain is very important source of water. It is the purest
form of water. Rain water can be stored in dam or pond and
later can be used. This water is used for drinking, irrigation,
bathing, cleaning, etc.

Underground water

The source of water which are found below the earth surface are
called underground water sources. When rain occurs, some of the
water seeps through the soil or porous rocks and goes down under
the surface of the earth. The seeped water is ultimately stopped by
a non-porous hard rock and gets collected there. An underground
layer of porous rocks, soil or sediments that store water is called

Times' Crucial Science Book - 9 236

aquifer. Aquifers range from a few square kilometers to thousand
square kilometers in
size. They contain
thousand times more Aquitard
water than that is
present in river, lakes water
and ponds. The level of table Aquifer
Aquitard
water under the
earth’s surface is
Artesian well

called water table. Aquifer
Since, the underground
water gets collected under the surface by seeping through soil and
rocks, it does not contain dust and dirt. But, it may contain germs,
gases and chemicals. The underground water does not become
VWDJQDQW ,W NHHSV RQ ÁRZLQJ DQG FRPH RXW WR WKH HDUWK VXUIDFH LQ
the form of spring, fountains, well, etc.

Fact Reason

Ogallala aquifer is the largest aquifer on the earth. It has
spread in 4,50,000 square kilometers in eight states of United
States of America.
When water freezes, there is increase in intermolecular
space between molecules. Due to which, ice has less density
than water and is lighter.
Water passed with high pressure through ‘water jet cutter’
can cut solids like wood, rubber, etc.

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.
. 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.

237 Times' Crucial Science Book - 9

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.

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.

:DWHU KDV D FDSDFLW\ WR ULVH LWVHOI LQWR D YHU\ ÀQH 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

Convex
meniscus

Water Mercury

Times' Crucial Science Book - 9 238

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.

Activity 14.1 To show the capillary action in a narrow glass tube.

Materials required:
$ ZDWHU WURXJK RU D EHDNHU D JODVV WXEH ZLWK ÀQH ERUH
etc.
Procedure:
7DNH D EHDNHU RU D ZDWHU WURXJK DQG ÀOO KDOI RI LW

with water.
'LS D QDUURZ JODVV WXEH ZLWK YHU\ ÀQH ERUH LQ WKH

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?
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
eiolenct(rHo3lOyt+e) due to chemical reaction. Then water acts as an
and conducts electricity.

H2O + HCl H3O+ + Cl-

Water Hydrochloric acid Hydronium ion Chloride ion

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

:DWHU $PPRQLD ń $PPRQLXP K\GUR[LGH

H2O + NH3 ń 1+4OH

239 Times' Crucial Science Book - 9

4. Water combines with sulphur trioxide to form sulphuric acid.

:DWHU 6XOSKXU WULR[LGH ń 6XOSKXULF DFLG

H2O + SO3 ń +2SO4
5. Water reacts with carbon dioxide gas to form carbonic acid.

:DWHU &DUERQ GLR[LGH ń &DUERQLF DFLG

H2O + CO2 ń+2CO3
6. Water reacts with alkali metals to form hydrogen gas and

metallic hydroxides.

2Li + 2H22 ń /L2+ +2
2K+ 2H22 ń .2+ +2
7. Water reacts with oxides, carbides and nitrides of some metals
to form metal hydroxides. Such reaction is called hydrolysis.

Mg3N2 + 6H22 ń 0J 2+ 2 + 2NH3
8. If steam is passed over red hot iron, they react to produce

hydrogen gas.

5HG KRW LURQ 6WHDP ń )HUURVR IHUULF R[LGH +\GURJHQ

3Fe + 4H2O O Fe3O4 + 4H2Ń
Fact Reason
Pure water is not a conductor of electricity, why?
Pure water doesn’t form ions so it is bad conductor of electricity.
If an acid or salt is added to it, it forms ions which help to conduct
the electricity.

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 S(CilvaeCrl2n),itrCaotpep(eArgNsuOlp3)h, aettec d(CisusSolOv4e), Potassium nitrate
(KNO3), in water. Similarly,

Times' Crucial Science Book - 9 240

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 into 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
ÀVK IDUPLQJ ,W LV XVHG IRU MHW FXWWLQJ 7KH SURFHVV RI FXWWLQJ
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.

8VHV IRU SODQWV We need water for the irrigation RI RXU ÀHOGV
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.

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.

241 Times' Crucial Science Book - 9

Activity 14.2 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.

3XW ÀYH GURSV RI VRDS VROXWLRQ LQ
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.

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.
wTanhhdeiletmhdaortlienockfuiclnaagrlcaifuonrmdmmbuialcakaerosbfoomnuaratgbenoinesseCisuaam(nHdbCitOceae3r)t2bh.oSsntuarctohengwi.saMterg(iHs CtaOs3t)y2

Times' Crucial Science Book - 9 242

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.
&DOFLXP ELFDUERQDWH ń &DOFLXP FDUERQDWH &DUERQ GLR[LGH
Water
Ca(HCO3)2 ń &D&23Ņ &22 + H2O
0DJQHVLXP ELFDUERQDWH ń 0DJQHVLXP FDUERQDWH &DUERQ GLR[LGH
+ Water
Mg(HCO3)2 ń 0J&23Ņ &22 + 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.
&DOFLXP ELFDUERQDWH &DOFLXP K\GUR[LGHń &DOFLXP &DUERQDWH :DWHU
Ca(HCO3)2 + Ca(OH)2 ń &D&23Ņ +2O
0DJQHVLXP ELFDUERQDWH &DOFLXP K\GUR[LGH ń 0DJQHVLXP
carbonate + Calcium carbonate + Water
Mg(HCO3)2 + Ca(OH)2 ń 0J&23 + CaCO3Ņ +2O
0DJQHVLXP ELFDUERQDWH &DOFLXP K\GUR[LGH ń 0DJQHVLXP
carbonate + Calcium carbonate + Water
Mg(HCO3)2 + Ca(OH)2 ń 0J&23 + CaCO3 + 2H2O

Activity 14.3 To remove the temporary hardness of water by boiling

Materials required:
Beakers, test tubes, dropper, soap, water, calcium
bicarbonate or magnesium bicarbonate, etc
Procedure:
7DNH D EHDNHU DQG ÀOO DERXW KDOI RI LW ZLWK

water.

243 Times' Crucial Science Book - 9

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:
<RX FDQQRW VHH ODWKHU IRUPDWLRQ LQ WKH ÀUVW FDVH %XW \RX ZLOO REVHUYH JRRG
lather in the second case.
Explanation:
1R ODWKHU IRUPDWLRQ RFFXUV LQ WKH ÀUVW FDVH EHFDXVH WKH ZDWHU LV KDUG GXH
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.

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. peCCMMrmaaaallaggccnnniiuueeenmmssiituucshmmhuallropscdruhhnilladpoetersheis(ad(CCoteeafa(C(wMSMlaO2gg)t4CeS)rlO2c)4a)nnot be removed by boiling. It
b.
c.
d.
The
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.

Times' Crucial Science Book - 9 244

a. Use of washing soda (tNhea2CsoOlu3.b1l0eH2sOal)t:s of calcium and
Washing soda reacts with
magnesium and turns them into insoluble forms. This removes the
hardness and the water becomes soft. While removing the temporary
hardness, soluble salts NaCl daondnoNt ac2aSuOse4 are also produced as the
side products. However, they the hardness of water.

&DOFLXP FKORULGH 6RGLXP FDUERQDWHń&DOFLXP FDUERQDWH
Sodium chloride
&DOFLXPCa VCXl2OS+KNDWaH2 C O 63 ńRG L&XDP& 2FD3ŅU E R Q D1WDH& ńO &DOFLXP FDUERQDWH
Sodium sulphate
SimilarClya,SO4 + Na2CO3 ń &D&23 + Na2SO4
0HJQHVLXP FKORULGH 6RGLXP FDUERQDWH ń 0DJQHVLXP FDUERQDWH
+ Sodium chloride
0DJQHMVLXgPCl 2VX+OSNKaD2WCHO 3 6ńR G0LXJP& 2FD3 U+ER2QNDaWCH 1ń 0DJQHVLXP FDUERQDWH
+ Sodium sulphate
b. UMsgeSOof4 P+ eNram2CuOti3t ńpr 0ocJe&s2s:3 + Na2SO4
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 isstaNnad2s(Afol2rSziOeo8)litbeu(tZ is
represented as Na2Z, in short form where 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:
CCMMaaggCSCSOlOl2244++++NNNNaaa2a2=2=2== ńńńń 0&0&DDJJ==== 1 111DDD2D2SS&&OOOO 44

245 Times' Crucial Science Book - 9

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 Soft water
two inlets and two outlets. Hard water Zeolite

is supplied through one of the inlets. Gravel
The other inlet is for adding sodium
chloride solution as per requirement.
The outlet that lies near the bottom of Permutit Process

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

&D= 1D&O ń 1D2Z + CaCl2

wa0stJe=w a t e r1cDon&tOa ńin i1ngD2cZal+ciMumgCaln2 d magnesium ions is removed
The
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
steomdapo(Nraar2yCOh3a)radnndescsauwshtiecresaods aw(NasahOinHg). Caustic soda softens the
hardness. soda softens permanent

Mg(HCO3)2 1D2+ ń 0J&23 + Na2CO3 + 2 H2O

MgCl2 + Na2CO3 ń 0J&23 + 2 NaCl

Times' Crucial Science Book - 9 246