Downloaded from https:// www. studiestoday.

com

In This Chapter You Will Learn :

>> importance of water sources of water and water cycle
>> potable water and its need purification of water to obtain potable water

yyy
>> water : a compound properties of water
>> hard water and soft water water pollution and control
Water management
. »» Effect of water scarcity on plants.

Molecular formula : H,0, relative Table 5.1 : Percentage proportion of water in

molecular mass-18 amu. One molecule of living things and common eatables
water contains two atoms of hydrogen and one | Living things and eatables | Proportion of water
Human beings 10%
_ atom of oxygen.
Elephants 80%
Chemical name: Dihydrogen monoxide.
Plants 60%
OF WATER Leafy vegetables 00%
5.1 IMPORTANCE
Potatoes 10%
Water is one of the most essential
Tomatoes 95%
substance for the existence of life. Since life
Turnips 88%
on the earth began in the oceans, and since no
Water melons 97%
living thing can survive without water, it is
Milk 95%
rightly called the source of life.
Eges (lg
Water forms a large part of the body mass Meat 75%
of all living organisms — 90% of human blood
is water. Water has the ability to dissolve a
number of substances. Therefore, it serves as ;
the liquid medium in which all reactions within | To show that dry substances contain water.
the living body take place. Take some dry splinters of wood in one
pieces of cloth in another
Fruits and vegetables contain waterinthem. _| test tube, very small dry
substanc es like wood, peas, test tube, and a few bean seeds in the third
Even dry- look ing
beans, grams, efc., contain some amount of water. test tube.

Downloaded from https:// www. studiestoday.com

|
n Downloaded from https:// www.studiestoday.com

WATER WATER WATER 5.2 SOURCES OF WATER

DROPLETS DROPLETS DROPLETS

Ss Water is widely distributed on the earth.

It covers nearly three-fourths of the earth’s |
surface.
Water exists in all the three states of
matter, i.e., solid as ice, liquid as water and
gas as water vapour.
: Pe : |
Under ordinary conditions, water is a |
liquid, and in this state it is present in oceans, —
Fig. 5.1 seas, rivers, lakes, ponds, etc. It is also present —
Heat them on a flame. What do you under the ground.
observe ? As the substances start getting
A considerable amount of water is found
charred, we see droplets of water getting
deposited on the upper part of the inner walls in the form of ice or snow in very cold regions
of the test tubes. of the world, viz. Arctic, Antarctica, and the
high mountains. Frost and hail are the other
Water is important forms of frozen water.
1. for everyday uses like cleaning, bathing In the atmosphere, water is present in the
and washing. form of water vapours, which condenses to
2. for drinking in order to satisfy our form clouds, fog, mist, efc.
biological needs.
3. for growing crops.
4. for various manufacturing processes. |
ie — Many municipal corporations are trying
5. for generating electricity. ; we
a ; water-harvesting techniques to improve the
6. for providing nutrients to aquatic plants availability of water.
and animals. — Find out what these techni
areque
and how
s -
7. It also helps to control the earth’s climate. they would increase the water that is available
8. Water regulates body temperature by the | for uses.
process of sweating and evaporation.
9. Water provides medium for all biochemical
reactions inside our bodies to take place.
10. Itis essential for the germination of seeds,
growth of plants and in photosynthesis.
11. Water inside the bodies of animals/humans _
dissolves minerals, gases and many Depending on its source and its degree
products of digestion and carries them at Of impurity, natural water is classified into the
place of need in the body. following types :
EE 78) ey
Downloaded from https:// www.studiestoday.com .
 Downloaded from https:// www. studiestoday.com

1. Ocean and sea water The taste of spring water differs from
place to place. Sometimes this water is
River and lake water
rich in minerals, which have medicinal
3. Spring and well water properties.
4. Rainwater.
A Rainwater : It is the purest form of
Sources of water natural water, and it is formed naturally
| |
Above surface
by evaporation followed by condensation
Surface water Underground water
—_1— i of water vapour in the atmosphere.
————
Rainwater dissolves the gases present in

| Ocean and
sea water
River and
lake water
Spring
water
Well
water
Rainwater the air, and also collects dust particles, as
it falls. Some of the important
dissolved in rainwater are carbon dioxide,
gases
1. Oceans and seas : Oceans and seas are
the largest sources of water, covering oxygen, nitrogen and sulphur dioxide.
nearly 71% of the earth’s surface. They Rainwater also carries smoke and germs
contain a very high proportion of present in the air. Therefore, the first
dissolved substances, mainly common shower of rain contains impurities, but
salt. Therefore, ocean and sea water are later showers are free from impurities, and
the most important sources of salt, but therefore safe for drinking.
they are not fit for direct consumption. A major portion of water on the earth is
2. Rivers and lakes (These are called present in the form of snow/ice. Most of
surface water sources) : Water in rivers the fresh water is frozen in glaciers and
and lakes comes from rain and melting polar ice caps.
snow. It also contains dissolved impurities
like salts, and suspended impurities like
clay, sand, twigs and living organisms not contain
To show that rainwater does
(germs). Rivers and lakes are the most
any dissolved impurities but well water
suitable sources of water for domestic and contains them.
industrial use. But this water needs to be
Take samples of rainwater and well water
purified before consumption, since it in two porcelain dishes. Keep the dishes
carries germs that can cause disease’. over two beakers containing water. Heat
Springs and wells : These are sources of them. As the water in the beakers boil,
underground water. This is the water that
WELL WATER
percolates through the upper layers of the
earth’s surface and gets collected on the
CONCENTRIC
solid rocks beneath. This water is next NO RINGS OF

only to rainwater in its purity. It contains

RESIDUE SOLID
RESIDUE

dissolved impurities, but it has no

suspended impurities or germs, since it is
filtered through the different layers of soil.
7
Downloaded from https:// www. studiestoday.com
 Downloaded from https:// www.studiestoday.com

the samples of water in the two dishes interconversion helps in balancing the amount
evaporate. of water both in the atmosphere and on the
What do you observe when both the earth’s surface, and is known as the water
samples have been completely evaporated ? cycle,
The dish containing rainwater has no
«_ WATER VAPOUR pis.
residue, but the dish containing well water has
concentric rings of solid residue. This proves
that rainwater is purer than well water.

10n

<RANSPIRAT/o,
@esP IRATIOW,
COMBUSs7
a. Do You Know ?

)
— Seas/oceans contain 97-4% of total
, Water available on the earth.
— The process of removal of dissolved | PLANTS —
HUMAN
salts from sea/ocean water is called| | ACTIVITIES ANIMALS |
desalination.
Fig. 5.3 : Water cycle (balances water in nature)
— In nature, water exists as snow on high
mountains. | Water is added to the atmosphere by the
— Most of the rivers, lakes, sea and | following natural processes :
oceans contain water in liquid form. _ 1. Evaporation from oceans, seas, rivers,
— Water exists as water vapour in the | ponds and lakes takes place due to the
atmosphere. atl heat of the sun.

5.3. WATER CYCLE

2. Burning of most fuels, mainly fossil fuels.
2C,H,9 + 130, heat 8CO, + 10H,O + energy
Water is considered a renewable resource _—__

on the earth. Water is a substance that is OR

capable of existing in all the three states of h a
Fuel + Oxygen heat Carbon dioxide + Water + Energy
matter. From one state it changes into another
3. Release of water due to respiration by
rather easily.
human beings, and animals [C.H,.0,
heat heat (glucose) + 60, — 6CO, + 6H,O + Energy].
Ice (3) == Water (1) ————= Water vapour
4. Transpiration by plants.
(O°C or cool (room cool or steam (g)
less) temperature) (100°C or more) Water that is released into the atmosphere
by these processes rises up in the form of
The change of water from one state to water vapours. These water vapours cool
another occurs all the time in nature. /t involves down as they rise, and form clouds in the
the process of evaporation, condensation and upper regions of the atmosphere. Clouds
precipitation (rainfall). This process of contain tiny droplets of water. As they move

i ial

Downloaded from https:// www.studiestoday.com

 Downloaded from https:// www.studiestoday.com

up and further cool, these droplets cling to cannot usually be consumed in its frozen
each other and form bigger drops, which state.
fall down as rain. Rainwater gets collected Only 1% of all the water on the earth is
again in seas, rivers, lakes, etc. This cycle available in rivers, lakes, springs, efc., to
goes on and on, therefore, it is called the
support life on land as well as for activities
water cycle.
like growing crops and manufacturing goods.
When water vapours cool rapidly well Therefore, this water is very precious to us,
below 0°C, they freeze into snow which falls and so it should be used wisely.
as snow flakes. But even this 1% of all water present
in rivers, lakes, wells and springs, cannot be
Importance of water cycle
used directly, because it contains many
1. Water cycle helps in regulating weather
on the earth. impurities.
2. Water cycle makes water available in Impurities Present in Water
various forms on the earth
Following types of impurities are found
in natural water.
1. Dissolved impurities : Since water is a
very good solvent it dissolves many
substances especially mineral salts in it.
These are mainly salts of calcium,
magnesium, sodium, etc. These dissolved
a. impurities cannot be seen through the
naked eye. Dissolved impurities can be
5.4 WATER AVAILABLE FOR HUMAN removed from water by distillation.
CONSUMPTION 2. Gases like oxygen, carbon dioxide, etc.
Water is necessary for all living beings. are also dissolved in natural water.
We cannot stay alive without water. 3. Suspended impurities : These are
The earth’s surface contains a very insoluble substances present in water.
large amount of water. About 71% of the They can be seen through the naked eye.
earth’s surface is covered with oceans and Suspended impurities are carried by water
seas. They constitute about 97% of the earth’s while it flows down the hills and plains.
total water resources. This water contain a very Common suspended impurities are: |
large amount of salts dissolved in it e clay and sand
(approximately 35 g per litre of water). e twigs, straw and leaves
Therefore, sea water cannot be used for human e decaying organic matter
consumption. e sewage, etc.
The polar ice caps account for 3% of the These impurities are removed by
world’s fresh water resources. But water filtration.

(Milianoe a. | 8) aaa a

Downloaded from https:// www.studiestoday.com

 ps:// www.studiestoday.com

Germs (Bacteria) : They are very small 5.6 PURIFICATION OF WATER TO OBTAIN
organisms present in water which can be seen ADEQUATE QUANTITY OF POTABLE
WATER
only through a microscope. They are harmful
and cause diseases like typhoid, cholera, To obtain adequate quantity of potable
diarrhoea, gastroenteritis, etc. water for cities and towns, the source of water
is usually a lake, or a river running nearby.
Germs can be removed by sterilization.
This water contains both suspended and
Therefore water needs to be purified dissolved impurities. Before supplying it for
before its consumption. This is done by drinking purposes, this water should be made
removing impurities and killing germs. free from these impurities. Doing this involves
the following operations :
5.5 POTABLE WATER (DRINKING WATER)
Sedimentation The settling of
AND ITS CHARACTERISTICS
suspended solid matter at the bottom of a
Water that is suitable for human liquid is called sedimentation, and the settled
consumption is called potable water or solid matter is called sediment.
drinking water, River water is pumped into basins, tanks
It should have _ the following or reservoirs, and allowed to stand for a few
characteristics : hours. Most of the suspended matter, like
1. It should be colourless and odourless. sand, clay and silt, settles down. The slower
the movement of water, the greater the
2. It should be clear and transparent.
possibility for the suspended matter to
3. It should be free from harmful micro- drop to the bottom as sediment. But very tiny
organisms that cause diseases and from particles settle down rather slowly. The rate
other suspended and dissolved impurities. of sedimentation of these minute particles is
4. It should contain the minerals* necessary increased by adding potash alum.
for our body, and also some gases, in Filtration : Filtration is the process by
order to add taste. which a liquid with insoluble, suspended fine
particles is allowed to pass through a filter.
5. It should be free from any harmful salts
The insoluble residue is left behind on the filter,
such as nitrates, cyanides, urea etc.
while clear liquid is collected in another
container as filtrate.
Saline water : Sometimes spring and well
water contains a greater amount of salt (2%) For water supply on a large scale, water
than is tolerable for direct use. Such water is filtered through beds of sand, charcoal and
gravel. This process removes suspended matter.
is called saline water. It is unfit for both
drinking purposes and irrigation. Sterilization : The process of removal of
germs is known as Sterilization.
The minerals are sodium, calcium, magnesium, iron, The filtered water may still contain germs
etc., but an excess of these minerals can be harmful. or bacteria which may cause water-borne

Downloaded from https:// www. studiestoday.com

 Downloaded from https:// www. studiestoday.com

‘ . Therefore they need to be removed.

Some of the methods to remove germs are :
(i) By exposure to air and sunlight : Air
containing oxygen and sunlight, both have Coagulation removes di and other particles suspended In water, Alum and 4
other chemicals ame added to water to lorm tiny sticky particles called “Tloc’
the effect of burning the germs to death. which attract the din particles. The combined weight of the dit and the alum
(oe) become heey encugh to ak to fe bosom dng sacentaon
When water in reservoirs is exposed to air
and sunlight over a large surface area, the Sedimentation
The heavy particles
germs are killed to some extent, but not (floc) settie to the
botiom
and he clear
Storage ; Water is
placed in a closed

completely because the rays of the water moves to hw tank or reservoir for
dwintection to take

sun cannot reach the lower layers of the

Disintection : A email amount of chlorine is added or some place. The water then
other disiniection method ia used to idl any bacteria of flows through pipes
thal may
microorg ania the water.
be in mna to homes and
water. distributed in the

(ii) By chemical treatment : Chemicals like

chlorine and ozone kill bacteria and other
germs present in water. Chlorine is
sometimes replaced by bleaching powder, Filtration : The water
passes § = through

for this purpose, which slowly reacts Mart, some made of

layers of sand, gravel,

with water to give chlorine and kills the and charcoal that
help remove even

germs. Treatment with ozone is called

ozonization. Swimming pools too are Fig. 5.4 : Large-scale purification
chlorinated to protect swimmers from the of water for drinking.

danger of infection. There are other household methods also

to get drinking water :
Aeration : Air under pressure is blown
(i) By boiling water
into the filtered water. This process is called
(ii) By water purifiers which are now made
aeration, kills harmful micro-organisms
available by different companies.
present in the filtered water.
Prolonged boiling is one more important
method of killing bacterias, but this method
can be applied over a small scale only.
Water after the removal of suspended
impurities and germs is collected in overhead
tanks and then supplied for domestic use
through pipes. Therefore the potable water so
obtained is also called “tap water”.
Tap water still contains dissolved UV water purifiers are
impurities which are mainly minerals and salts
necessary for our body. But excess of these
may not be good for health.

Downloaded from https:// www. studiestoday.com

 Downloaded from https:// www. studiestoday.com

(iii) By adding calculated amount of chlorine

Distillation flask
Thermometer

to the water stored in tanks on the roofs

of houses to kill the germs. Liebig's
condenser

(iv) By filtration — Any suspended

impurities in water from well, river, or To sink
Bunsen
lake can be removed by filtering water burner

through a fine muslin cloth

Fig. 5.5 Distillation

passes through the Liebig condenser. Steam

again changes into liquid water through cold
contact and gets collected as distillate (distilled
and washing because it contains h water) in the receiver.
concentration of salts. It induces v: nitin ; The dissolved impurities remain in the
5.7 PURIFICATION OF WATER BY flask. Therefore, by this process both the
dissolved solids and pure water are recovered.
DISTILLATION
Distillation : The process of converting Distilled water is used
a liquid into vapour by heating and the (i) for preparing solutions for medicinal
subsequent condensation of the vapour, back purposes.
into a liquid is called “‘distillation”’. (ii) for experiments in the laboratory.
This method is used to remove dissolved (iii) for car batteries.
impurities from water. The water obtained after But it cannot be used for drinking
distillation is called distilled water. It is the purposes because it does not contain any salt
purest form of water. and minerals which are necessary for the
proper growth of our bodies. Also it does not
Impure water is kept in the distillation
contain any gas due to which it is flat to taste.
flask and boiled water turns into steam and

1. Name the four main sources of natural water. 5. How is water purified on large scale to make it
2. How is water added to the atmosphere ? How potable? Explain all the steps.
does this water come back on the earth ? What 6. List three household methods to get drinking
is the process known as ? water.
3. What is potable water ? Give three main
7. What is distilled water ? What are its uses?
characteristics of potable water.
4. 8. Give reason :
What are the three main types of impurities
present in water ? How can they be removed (a) Distilled water is flat to taste.
from it ? (b) Distilled water is not suitable for drinking.

' Downloaded from https:// www. studiestoday.com

 Downloaded from https:// www. studiestoday.com

15.8 WATER : A COMPOUND electrode, is double that of the volume of gas

collected in tube A, inverted over the positive
. Water has been used by man ever since
electrode. Keep passing current until the test
he came into existence. Owing to its high tube at the negative electrode (cathode) is
“stability, water was initially considered to be completely full of gas. Then stop passing current
an element. Henry Cavendish, in 1781, proved and take out the test tubes for testing the gas.
‘that water is a compound made up of two A—{
(0,~2 Piao
H, EB

elements : hydrogen and oxygen. He obtained 8 0 Ps

TEST TUBES
°
water by burning hydrogen in air with the o o
ACIDIFIED jo HOFFMAN'S
Jhelp of an electric spark. The conclusion WATER (HOT)—} | 2 °| T-VOLTMETER
\made by Cavendish (about water) was later |
= ELECTRODES
_ supported by Lavoisier. _———————

Water breaks up into its constituent

F— ELECTRICAL
yelements, viz. : oxygen and hydrogen when CIRGUT
Li] &
\heated to a temperature of 2000°-3500°C or |
Fig. 5.6
_ when an electric current is passed through it.
When a burning splinter is brought near
' But for this process to take place, water must
test tube B, the gas burns with a pop sound,
contain a small amount of salt or acid in it. indicating that the gas is hydrogen.
This process is called electrolysis. But when a glowing splinter is brought near
the mouth of test tube A (inverted over the
The process of breaking down of a
positive electrode), the splinter bursts into a
compound, which is in a molten or a flame, indicating that the gas is oxygen.
solution form, by passing an electric current Thus, from the above experiment, it is clear
hrough it, is called electrolysis. that water is formed by the combination of two
elements, hydrogen and oxygen, in a definite
proportion of 2: | by volume.
From whichever source water is taken, it
has the same chemical composition. One
‘Take an apparatus called Hoffman's molecule of water is represented by the formula
tmeter. Fill it with acidified water, and invert H,O. The chemical name is Dihydrogen monoxide.
electric
a0ORT coment 2H, + O,
des of the apparatus, so that they are
Cathode is the negative electrode whereas
| in water, Connect the electrolytic cells
battery with the help of a wire. anode is the positive electrode in an electrolytic
cell.
Now pass an electric current through the
For electrolysis of water, acid or salt is added
will shapve.tthat, in both the tubes,
to it, because pure water is a bad conductor of
electricity. Hydrogen is obtained at the cathode
and oxygen is obtained at the anode.

Downloaded from https:// www.studiestoday.com

 Downloaded from https:// www. studiestoday.com

PHYSICAL PROPERTIES OF WATER The pressure under a skater’s shoes melts |

Wn fi

Pure water is a colourless, transparent the ice, which freezes again when the:skater | _
-

liquid at room temperature. It is tasteless moves on. This results in melting of snow
and odourless, too. The water we drink because of an increase in pressure, and the |
has taste because it contains dissolved skater glides on water.
substances.
The freezing point of pure water is 0°C. The effect of impurities present in water
MN

This is the temperature at which water Any impurity present in water lowers its
starts changing into ice. The temperature freezing point and raises its boiling point.
remains constant at the freezing point till
For example, salt is added to ice to lower
all the water has frozen. its melting point. Such a mixture is called a
The melting point of ice is also 0°C,
td

freezing-mixture. The melting point of the

.

which is the temperature at which ice

freezing mixture is about —15°C.
Starts changing into water. The
temperature remains constant till all the Similarly, alcohol is added to the water
ice has melted.
used in car radiators to prevent it from freezing
4. The boiling point of water is 100°C in cold weather.
Under normal pressure it is the Why doesn't sea water freeze so easily ? |
temperature at which pure water boils

=—
and starts changing into steam. The 5.10 SPECIFIC HEAT OF WATER

—
temperature remains constant till all the
Water has high specific heat*. This means

ee
water has boiled and changed into steam.
that water needs a large amount of heat to

oS—0UlC
The effect of pressure on the boiling and become hot, and it needs to lose a large amount

wz
freezing points of water of heat to become cold. In other words, water

,=
The boiling point of water decreases with neither heats up nor cools down quickly.
a decrease in pressure, and increases with an This property makes water an excellent
increase in pressure. Therefore, water boils at cooling agent. Water is used as a cooling agent
a lower temperature in the hills, where the in car engines, factories, nuclear reactors, efc.
atmospheric pressure is lower than in the It absorbs the heat produced in an engine or a
plains. That is why it takes a longer time to machine or some other part of a factory, and
cook in hilly regions. prevents it from becoming too hot.
Water also acts as a natural cooling agent.
Land breeze and sea breeze occur due to this 7

property of the high specific heat of water.

Sea breeze and Land breeze take place
in the coastal regions due to which those
* The specific heat of a substance is the amount of heat required
to raise the temperature of a unit mass of that substance by
one degree centigrade.

Downloaded from https:// www. studiestoday.com

a Downloaded from https:// www. studiestoday.com

:
regions have moderate climate, i.e., neither too 5.11 ANOMALOUS EXPANSION OF WATER
hot nor too cold. [RELATIVE VOLUME AND DENSITY OF
Sea breeze : The flow of cold air from ICE AND WATER]
_sea to land during daytime is called sea breeze. The density of a substance is its mass per
‘As water has high specific heat, the land unit volume, while volume is the space
‘becomes hot earlier than sea water during day occupied by the mass of the substance. Usually,
time. The hot air above the land rises up and the solid form of a given substance has greater
the cold air above sea water flows towards the density, and it is also heavier than the liquid
land. Thus the days are not very hot in those form (for the same volume).
areas.
: HOT AIR In the case of water, its solid form (ice)
COLD AIR is lighter than its liquid form. This is an
anomalous phenomenon also called as
anomalous expansion of water.
! Generally, when something is heated, it

| Fig. 5.7 : Sea breeze (during daytime)

expands and its density decreases, and when
it is cooled, it contracts and its density
Land breeze : The flow of air from land increases. Accordingly, when water is cooled,
to sea at night is called land breeze. At night it contracts and its density increases, but only
the land becomes cold sooner than sea water. until the temperature reaches 4°C, because on
As a result, the hot air above sea rises up and further cooling, water starts expanding, with a
the cold air from land moves towards the sea. decrease in its density, which is an anomalous
Thus, the nights are not very cold in coastal phenomenon. At 0°C, it becomes ice, and this
areas. ice floats on water. The density of water 1s,
COLD AIR therefore, the greatest at 4°C, which is equal
to 1 gm/cm? or 1 kg/litre.
Freezing lakes The anomalous
expansion of water is a great boon to aquatic
life in cold regions. When the temperature
falls, the water on the surface of lakes initially
Fig. 5.8 : Land breeze (at night)
cools and contracts. The heavier, colder water
Why is water used in room coolers-and. sinks, and the surface water again cools. This
| hot water bags ? process continues till the temperature reaches
4°C. On further decrease in temperature, the
surface water expands and becomes lighter.
Now it does not sink. Therefore, further
cooling takes place only at the surface, while
the temperature of the lower layers of water
does not change. Eventually, the water at the

Downloaded from https:// www. studiestoday.com

 Downloaded from https:// www. studiestoday.com
7

surface changes into ice, which floats over the The capacity of water to dissolve
water below. Ice is a poor conductor of heat substances, and its importance as a solvent,
and acts like a blanket that protects the bottom can be explained by the following activity.
layers of the water from the cold air above.
This is how fish and other living organisms
live inside lakes during winter, even though
there is ice at the surface. As the temperature Take some water in a glass. Add some sugar
dips further, the thickness of the surface of to it and stir properly. You will observe that all |
ice increases. the sugar disappears. It means that sugar has been
dissolved in the water. Add some more sugar to
it. Again it dissolves. Go on adding sugar to the
ICE AT 0°C OR oe ae solution formed in the glass, till no more sugar
EVEN LOWER ve | RISING
Y TEMPERATURE OF dissolves in it.
2c
af aeose 5 Ssh \y WATER
= ac '
This solution is said to be saturated, while
NW SDENSEST LAYER OF
4°C WATER AT 4 °C the solution that can keep dissolving more solute
Fig. 5.9 : The topmost layer cools and ultimately at a particular temperature, is said to be
freezes, while the bottom layers remain at 4 °C unsaturated.
}
In the colder parts of the world, water pipes Now, heat the solution. You will observe
burst when the water inside them freezes in that the sugar that was not dissolved earlier, now
winter. Why ? gets dissolved.

5.12 WATER — AN EXCELLENT SOLVENT

A liquid, which dissolves another
substance to form a solution, is called a solvent.
The substance that dissolves in the solvent
is called the solute, while a solution is SUGAR UNDISSOLVED ALL SUGAR
SOLUTION SUGAR DISSOLVES ON
the homogeneous mixture of solute and HEATING
solvent. Fig. 5.10
This solution is said to be supersaturated.
Solution = Solvent + Solute
This shows that water has a great capacity to
Water is often termed the universal dissolve substances. |t also shows that an increase
solvent, because it dissolves almost all kinds in temperature increases the dissolving capacity
pacity.
of solid, liquid and gaseous substances. Where of water.
a = i —f

the amount of the solute may be more or less. Conclusion : Water can dissolve a su bstance.
Water can even dissolve the minute but only upto a limit. ae
particles of the container in which it is kept. It
e Solid substances like salt, sugar, baking
even corrodes our internal body parts if drunk
in its purest form (distilled water). soda, washing soda, etc., readily dissolve
in water.

Downloaded from https:// www. studiestoday.com

 Downloaded from https:// www. studiestoday.com

Liquids like fruit juice, alcohol, vinegar, Effect of pressure on the solubility of a
etc., also dissolve in water. Such liquids substance (solute) in water
are called miscible liquids. e Pressure has practically no effect on the
solubility of a solid (solute) in water.
rhe Boule aehich do not dissolve in water
e In the case of gases, the amount of a gas
dissolved in water increases with an
increase in pressure and decreases with
Many gases like oxygen, carbon dioxide a decrease in pressure. That is why
and ammonia also dissolve in water. carbonated drinks (cold drinks, soda etc.)
which contain carbon dioxide are bottled
under high pressure, i.e., they contain a
large amount of gas in them.
of any substance in v When we open a bottle of a carbonated
ous solution. i
drink, some of the gas comes out with a
hissing sound. Why ?

5.13 THE IMPORTANCE OF THE GASES

AND MINERALS DISSOLVED IN
( i Effect of temperature on solubility of a
NATURAL WATER
ubstance (solute) in water
1. Natural water contains dissolved
© Solubility of a solid solute generally
gases like oxygen, nitrogen and carbon
increases with an increase in temperature.
dioxide.
This makes it possible to prepare
e Oxygen dissolved in water is the main
supersaturated solutions.
source of survival for marine life.
e Solubility of a gas decreases with an e Carbon dioxide dissolved in water is
increase in temperature. That is why used by plants for photosynthesis.
gases dissolved in water can be easily
e Nitrogen in water converts into
expelled by boiling. Boiled water has a
nitrogenous compounds by the action
flat taste.
of bacteria and serves as a mode of
nourishment for water plants.
2. Some of the salts dissolved in natural
water are essential for the proper growth
of our bodies. They also add taste to
drinking water.
3. Sea water contains a large amount of
common salt(sodium chloride) dissolved
in it.

(>ie
Downloaded from https:// www. studiestoday.com
 Downloaded from https:// www.studiestoday.com 5

~e
Evaporation of sea water gives solid B. On non-metals :
common salt, which is an essential (i) Non-metals like carbon (coke) reacts
ingredient of our food. It is added to our with steam to produce water gas,
food for taste and for the proper growth and which is an important industrial fuel.
development of our bodies. Coke + Steam —1000°C_, Water gas.
C+H,O_1000C_, [co +H]
Chemical properties of water
(red hot) Water gas
1. Pure water is neutral to litmus which
(ii) Chlorine gas dissolves in water to
means that no change in the colour of blue
produce chlorine water, which contains
or red litmus solution is observed when
hydrochloric acid and releases oxygen
treated with water.
gas on exposure to light.
2. Action of heat or electrolysis : Water is a
Cl, + 2H,O_sunlight_, 2HCI + O,
highly stable compound. However, when
heated above 2000°C or when electric
current passes through water, it
decomposes into hydrogen and oxygen To find out if the given substance is soluble
gases. or insoluble in water.
Materials required: A few substances like
2H,O _2000°C_, 2H, + O,
common salt, sugar, starch, sulphur, alcohol ane
or electrolysis
test-tubes.
3. Action of water on elements : Procedure: Take about 5 mL water in each,
A. On metals : Water reacts with active of the five test-tubes and place them on a|
test-tube stand. Add a pinch of common salt in
metals like sodium, potassium,
test-tube 1, of sugar in test-tube 2, of starch in
magnesium, calcium, iron, efc., under
test-tube 3, of sulphur in test-tube 4 and about
different conditions to produce
1 mL of alcohol in test-tube 5. Shake each
hydrogen gas. test-tube for a while and put the test-tube back
Sodium + Water —fast_, Sodium + Hydrogen to the test-tube stand. Note, if the substance
(cold) hydroxide dissolves in water or not. From the experiment
2Na + 2H,O -——» 2NaOH + H,(g) you will observe the following results :
(cold) Test-tube Substance Soluble or insoluble
Calcium + Water —Slow_, Calcium + Hydrogen Common salt Soluble
hWwWN

(cold) hydroxide Sugar

=a

Ca+2H,O ——, Ca(OH),+ H,(g) Sulphur

Magnesium + Steam ——_» Magnesium + Hydrogen Alcohol
wn

oxide Conclusion : Common salt, sugar an d

Mg + HO —— >. Ms0OU4 H,(g) are solubleublein inwater , whereas starch ar
(steam) are insol water.

Downloaded from https:// www.studiestoday.com

 _ Downloaded from https:// www. studiestoday.com

: 4. Action of water on compounds : Test for Water

A. On metallic oxides : Water dissolves 1. Water can be tested by its boiling point
metallic oxides like sodium oxide, (100°C) and freezing point (O°C) if it is
; potassium oxide, efc., to produce pure.
metallic hydroxides also known as
2. When a few drops of water are added to
alkalis.
anhydrous copper sulphate powder, its
Sodium oxide + Water ——-» Sodium hydroxide
colour changes from white to blue.
(alkali)
Na,O + H,O ——, 2NaOH
Potassium oxide + Water —__, Potassium hydroxide
(alkali)
K,0 +H,O ——, 2KOH
Calcium oxide + Water ——_» Calcium hydroxide
(alkali)
CaO +H,O ——, Ca(OH),
B.
On non-metallic oxides : Oxides like
carbon dioxide, sulphur dioxide,
nitrogen dioxide, efc., dissolve in water
Fig. 5.11: Adding water to white copper
to produce acidic solutions.
sulphate turns them blue
_ Carbon dioxide + H,O ——, Carbonic acid
CO, +H,0 ——, 1,Co, 3. When a few drops of water are added to
“Sulphur dioxide + Water ——+ Sulphurous acid blue cobalt chloride its colour changes
SO, + H,O ——» H,SO, into pink.
= ——_— = Seag

‘1. Define the following terms : (c) Water pipes burst in severe winters.
(a) Melting point (b) Boiling point (d) It is difficult to cook in hills as compared to
(c) Specific heat (d) Solvent plains.
(e) Electrolysis (f) Sterilization (e) Ice floats on water.
(g) Solubility (f) Sea water does not freeze at 0°C.
2. Name the two gases from which water is formed. (g) Small amount of acid is added to water before
What is the chemical composition of these two electrolysis.
gases in water ? Give the molecular formula of 5. How does anomalous expansion of water help
water. aquatic organisms in cold climates ?
3. Name the products formed when water reacts with 6. Give balanced chemical equations for the following:
(a) sodium (b) calcium (a) Magnesium + water — magnesium oxide
(c) calcium oxide (d) carbon dioxide + hydrogen
4. Give reasons: (b) Carbon dioxide + water — carbonic acid
(a) Water is used as a cooling agent. 7. Give two examples for each of the following :
(b) Distilled water should not be used for drinking. (a) Miscible liquids (b) Immiscible liquids

‘ ; ——

Downloaded from https:// www. studiestoday.com

 Downloaded from https:// www.studiestoday.com

Differences between hard water and soft water

5.14 HARD WATER AND SOFT WATER
Hard water Soft water Tq
'*

The water present in different natural

sources has different substances dissolved in 1. Hard water does not 1. Soft water easily
it. It has been found that water drawn from easily form lather forms lather with |
with soap. soap.
certain sources forms a lather with soap rather
easily. Such water is called soft water. 2. It is not good for}2. It is good for
drinking or making drinking or preparing
Whereas, water obtained from some other solutions or washing solutions or washing
sources does not easily form a lather with soap, clothes. clothes,
rather it forms a white sticky scum or a
precipitate. This water is called hard water. 5.15 DISADVANTAGES OF HARD WATER
1. Hard water is not safe for drinking.
Hard water is of two types : 2. It results in wastage of soap.
(i) Temporary hard water : Water, which 3. It leaves a substance at the bottom of the
has bicarbonates of calcium and container when it is boiled. This
magnesium dissolved in it, is substance is called scale (or fur) which
temporary hard water. This kind of damages the container. .
hardness can be easily removed by 4. Hard water is not suitable for preparing
boiling. solutions.
5.16 CAUSES OF HARDNESS OF WATER
WATER
Temporary hard water is formed when
On the basis of lather formation with soap
| rainwater containing carbon dioxide flows over
Soft Water Hard Water rocks made of calcium or magnesium
(forms lather (does not form lather easily with soap)
easily with soap |
carbonate. This results in the formation of their
Temporary hard water Permanent hard water bicarbonates, which dissolve in water, making
(Due to bicarbonates (Due to chlorides and it temporarily hard.
of calcium and sulphates of calcium
magnesium) and magnesium)
5.17 REMOVAL OF HARDNESS OF WATER
Hardness can be Hardness can be The hardness of water is to be removed
removed by simple removed by chemical
to make it consumable in homes, laundries,
physical method, method, i.e., by adding
boiling sodium carbonate factories, etc. When dissolved salts of calcium
and magnesium are removed from water, it
(ii) Permanent hard water : Water, which becomes soft. The following are some of the
has sulphates and chlorides of methods used to remove the hardness of
calcium and magnesium dissolved in it, water.
is called permanent hard water. 1. Boiling : This method helps to remove
This hardness cannot be removed by only the temporary hardness of water.
boiling. When temporary hard water is boiled, the

Downloaded from https:// www.studiestoday.com

 | Downloaded from https:// www. studiestoday.com

| bicarbonates of calcium and magnesium (ii) Add some washing soda (Na,CO,'10H.O)
break up to form their respective in beaker B and stir. A white insoluble solid
insoluble carbonates. These can be (CaCO,) is formed. Allow it to settle and
filtered out so that water becomes soft. then filter it. Now add some soap solution
to this water and stir.
Ca(HCO,), __boiled_, CaCO, + H,O + CO,(g)
What are your observations ?
(soluble calcium (ppt) (water) (carbon
bicarboate) (calcium dioxide) You observe that in beaker A no lather has
carbonate) formed but in beaker B, lather is formed.
_ _Mg(HCO,), _boiled_, MgCO,
+ H,O + CO,(g) This is because beaker A contains hard water
_ (soluble magnesium (ppt) (water) (carbon but the water in beaker B becomes soft on |
bicarboate) (magnesium dioxide) adding washing soda.
. carbonate)

| 2. By adding sodium carbonate : The

permanent hardness of water is removed ven is |
FORMED Soa
when such water is treated with a small
quantity of sodium carbonate. It reacts NO cadena TA aga
LATHER |S
with the soluble chlorides and sulphates FORMED

of calcium and magnesium to form their Fig. 3.12 |

respective insoluble carbonates. These
can be removed by filtration and then the
water becomes soft. Sodium sulphate or
=/
(Baio Kaw?
sodium chloride formed after the reaction
Detergents act on the same way as soap
does not affect the soap.
but they do not form scum with hard water.
Na,CO, + CaSO, —~» CaCO, + Na,SO,
(sodium (calcium (insoluble _— (soluble 5.18 WATER POLLUTION
| carbonate) sulphate) calcium sodium
carbonate) sulphate)
Water pollution is the contamination of
Na,CO, + MgCl, —> MgCO, + 2NaCl water which makes it unfit for many type of
(sodium (magnesium (insoluble (soluble
carbonate) —_ chloride) magnesium sodium uses, i.e., undesirable changes in the physical
carbonate) chloride) chemica! and biological conditions of water
that make it unfit for human consumption, is
———————

called water pollution.

Take some tap water in beaker A. Add a The pollution of fresh water is one of the
pinch of magnesium chloride to it and stir so most serious environmental problem faced by
that it gets dissolved. Now the tap water has the world today. The water present in rivers,
become hard. Pour half of that water in another ponds, lakes and streams, comes from rain and
beaker B.
the melted snow of the mountains. As it flows
(i) Add some soap solution in beaker A and
down the plains, it picks up many dissolved
stir.
and suspended impurities. This water further

Downloaded from https:// www. studiestoday.com

 Downloaded from https:// www.studiestoday.com

increases in its impurity by the addition of | 2. Nuclear and thermal power plants :
the waste products from homes, agricultural Power plants use large amounts of water
lands and industries. These waste products are for cooling purposes. They discharge the
very harmful. They are called pollutants, resultant hot water, often containing
because they make the water impure and chemicals, into water streams. This
polluted. results in an increase in the temperature
of water, which is injurious for fish and
5.19 CAUSES OF WATER POLLUTION other aquatic life forms. 7

1. Industrial and agricultural processes : e Contamination of rivers, lakes, efc.,

Water is required in large quantities in with heavy metals like lead, mercury,
industries and in agriculture for different copper, nickel, efc. can harm both
purposes. But care is not taken to keep aquatic and human beings.
the water fit for consumption. Most of
the industries dump their wastes in rivers
and even into the sea.
Fertilizers, pesticides, insecticides and
other chemicals used in cultivated fields,
get dissolved in water when it flows
across these fields. This adds undesirable
chemicals into the water. Acidic water
from mines and acid rain also pollute the
water in rivers and seas. These chemicals
are dangerous for aquatic life, and they
make the water unfit for consumption.
Fig. 5.14
PICTURES SHOWING WATER POLLUTION 3. Sewage and garbage : The discharge of
sewage and garbage into river water is
another major cause of water pollution.
Water becomes unsafe for drinking and
other uses due to people urinating,
defecating or washing in it. Different —
kinds of germs grow that causes diseases
Cholera bacteria
in polluted water.
passed with
faeces Almost two-thirds of all the illnesses in
Cholera bacteria
multiply in warm
India are water-borne, such as typhoid,
water hepatitis, cholera, diarrhoea, dysentery,
etc.

' Downloaded from https:// www.studiestoday.com

 Downloaded from https:// www. studiestoday.com

9. Purification of water bodies should be

The chemical wastes of factories and
fertilizers and pesticides used in agriculture carried out off and on.
cause chemical pollution of water when 10. Dead bodies of animals should be
they are dumped into rivers, lakes, ponds, disposed of in a hygienic way.
etc.
While hot water from factories and 5.21 EFFECT OF WATER SCARCITY ON
thermal plants when mixed with fresh water PLANTS
cause thermal pollution.
You have already learnt that water is
5.20 PREVENTION OF WATER POLLUTION needed by plants for various purposes. If water
is not available to plants for long the earth
1. We should spread awareness and make
will lose its green character.
sanitary facilities available in rural areas
and city slums so as to discourage people Human being are dependent on plants.
from defecating in the open. Plants provide food, oxygen, wood and many
other useful products. If there are no plants,
2. Domestic sewage should be treated before
there will be no life on earth.
being discharged into rivers.
3. The solid matter separated from sewage 5.22 WATER MANAGEMENT
can be used to generate biogas, an Water is a precious natural resource. In
important alternative fuel. order to make water easily available to us in
4. The waste products of industries should future, we have to conserve it today. A few
be treated before they are discharged into ways by which water can be conserved are as
rivers and other water bodies. follows.
5. We should try to stop using substances 1. Construct dams and reservoirs to control

like detergents, pesticides, polythene, etc. flood and collect water.

They are non-biodegradable and they 2. Do not leave taps running while brushing
pollute the environment, including water, teeth, shaving or washing clothes.
to an undesirable extent. 3. Recycle water in industries and use it as
many times as possible, before disposing
6. Washing and cleaning of utensils, clothes,
it.
bathing of animals and human beings
should be avoided near the sources of 4. Plant trees to slow down the flow of
rainwater on land and to increase seepage
water like rivers, lakes, etc.
of water into soil.
7. Trees and plants must be planted along
5. Practice rainwater harvesting.
the banks of rivers.
6. Repair leaking taps and pipes at the
. Put a covering on the well. earliest.

Downloaded from https:// www.studiestoday.com

 Downloaded from https:// www.studiestoday.com

7. Recycle polluted water and use it for 9. Farmers should use better methods of
irrigation. irrigation like drip irrigation in which
8. Use biodegradable fertilizers and water is supplied to plants drop by drop
pesticides. instead of filling the entire field with
water.

a ( RECAPITULATION)
@ Water is the source of life for all living organisms.
@ In Nature, water occurs in all the three states of matter, i.e., ice, liquid and vapour, but mostly in liquid form.
# Water found in nature comes from :
(i) Oceans and seas (ii) rivers and lakes (iii) springs and wells (iv) rain
* Rainwater is the purest form of water. Sea water is very impure, as it contains a very high proportion of
dissolved salts.
Potable water should be free from suspended impurities and harmful germs, but it should contain some
4

dissolved minerals and gases for taste and health purposes.

Water is a compound with the molecular formula of H,O.
§

The boiling point and the freezing point of water are affected by change in pressure and presence
of impurities.
0°C is also called triple point because water can exist in all its three states at this temperature. 1
2.7

The specific heat of water is higher than that of any other liquid. Consequently, it is used as scooling agent. |
Water has minimum volume and maximum density at 4°C. It starts expanding below 4°C. This is called
anomalous behaviour of water. ~ ”

its
Bao
a

Sr

=%
q

=
=
=A

ot
a

5
a

zB
o

e
ag

o
“o

o
B
2
EL
<
o
5
§g
"g
ae

yee
ee

or ‘hard’. Hardness of water can be removed by boiling or by chenitesl indaudell

Water pollution is a serious problem. It is ie gaa to control water rear

l. Define: 3. Differentiate between chemical and thermal water

(a) Soft water (b) Hard water pollutions.
2. What are the causes of temporary and permanent | 4, What are the main causes of water pollution ? How
hardness of water ? Suggest one method for the can it be:controlled'?
removal of hardness of each type and give chemical
equations for them. 5. Name three water borne diseases.

Downloaded from https:// www.studiestoday.com

 Downloaded from https:// www. studiestoday.com

1. Fill in the blanks : 3. Give one word/words for the following

(Ye @ Water HES acaccortscsenesesceos density and statements :

See ae peadiiea Asiwd volume at 4°C. (a) Water fit for human consumption ..............

(b) Freezing mixture CONTAINS ......... cece (b) The harmful substances dissolved in water
BINNc Aced sees eeeis!
(c) The solubility of a gas in water ........ (c) The change of states of water from one
-vsseeseeee With rise in temperature and POLI LOVAHOLNET 5 -tecc scree -ceoes--s
paeeusy eoupecebeca with rise in pressure. (d) The gaseous form of water found in air
(ay, Pies isthe purestformofnatural water, | rsssseeeeeteeseeesees

(e) WISE OF artilicial’....-..-....-.0:...... by farmers (e) Amixture of common salt and ice.............
{lution.
causes water powuuon. MULTIPLE CHOICE QUESTIONS
(i) Boilie removes the ......5.2.-......5.+6
1. Two gases dissolved in natural water are
hardness of water.
(a) oxygen and carbon dioxide
| Water turns the colour of anhydrous (b) hydrogen and oxygen
(8) papuer eniphate y
PP wma (c) sulphur dioxide and hydrogen
(h) Water gas is a mixture Of .................-++ (d) chlorine and ammonia
AD sosessssonctesseseseees : 2. The sticky substance formed when soap is added
| 2. State whether the reasons given in column to hard water is
B correctly explain the statements given in (a) scum (b) lather
| column A Cay ak
| (c) residue (d) precipitate

| Column A. Sannin 8 3. Temporary hardness of water can be removed

(a) Acid is added to To make it alkaline by
water before it is (a) filtering (b) boiling

electrolysed. (c) loading (d) none of the above

(b) Alcohol is mixed Because it lowers . a
: 4. Water is sterilized by
with the water used _ the freezing point (a) nitrogen gas (b) oxygen gas
: : iaymeydroren.pas
in car radiators of water (uichion
(c) Icebergs float in Because ice is not eee yas
ocean water A saline substatice 5. The ultimate source of all water on the earth is
(d) Carbonated drinks —_ Because the (a) oceans and seas
are bottled under solubility of (b) spring and wells
high pressure carbon dioxide (c) rivers and lakes
increases with eran
pressure.
a St = —

PROJECT ACTIVITIES)
% | poster competition in your school for importance of water resources. Also
ec campaigna
fo conserve water

(a 7 |

Downloaded from https:// www.studiestoday.com

 Downloaded from https:// www.studiestoday.com

7. Recycle polluted water and use it for 9. Farmers should use better methods of
irrigation. irrigation like drip irrigation in which
8. Use biodegradable fertilizers and water is supplied to plants drop by drop
pesticides. instead of filling the entire field with
water,

@ Water is the source of life for all living organisms.

In Nature, water occurs in all the three states of matter, i.e., ice, liquid and vapour, but mostly in liquid form.
wv

# Water found in nature comes from :

(i) oceans and seas (ii) rivers and lakes (iii) springs and wells (iv) rain
# Rainwater is the purest form of water. Sea water is very impure, as it contains a very high proportion of
dissolved salts.
Potable water should be free from suspended impurities and harmful germs, but it should contain some
q

dissolved minerals and gases for taste and health purposes. i, |

, Ui

Water is a compound with the molecular formula of H,O.

Totes,§

The boiling point and the freezing point of water are affected by change in pressure and presence of impuritic S.)
0°C is also called triple point because water can exist in all its three states at this temperature. wa
The specific heat of water is higher than that of any other liquid. Consequently, it is used
as a coolir

anomalous behaviour of water.

Water is an excellent solvent. The gases dissolved in water have biological importance.
4

life to sustain itself. 7

@ Water may form lather with soap easily, or it may not do so easily. Depe: d
or ‘hard’. Hardness of water can be removed by boili by chem
orng
* Water pollution is a serious problem. It is necessary to control water pe |

1. Define: 3. Differentiate between chemical and thermal water

(a) Soft water (b) Hard water pollutions.
2. What are the causes of temporary and permanent | 4, What are the main causes of water pollution ? How
hardness of water ? Suggest one method for the can it be controlled 9
removal of hardness of each type and give chemical
5. Name three water borne diseases.
equations for them.
a =

Downloaded from https:// www.studiestoday.com

 Downloaded from https:// www. studiestoday.com

3. Give one word/words for the following

1. Fill in the blanks :
statements :
(en Water Nasiiccrc ccavcccees orceses density and
reoreu mace ciersvice volume at 4°C. (a) Water fit for human consumption ............».

(b) Freezing mixture CONtAINS ...........cceeee (b) The harmful substances dissolved in water
EGY eek ta eA orctne eee eee SPREE Reese e ees

(c) The solubility of a gas in water ........ (c) The change of states of water from one
.. with rise in temperature and form tO ANOTNET ...........:eeeeeees
piceuysyaktecuasasaan with rise in pressure. (d) The gaseous form of water found in air
Cay plea iit is the purest form of natural water. See eee eee eee eee eee

(e) Use of artificial ...............000:... by farmers (e) A mixture of common salt and ice.............
causes water pollution. MULTIPLE CHOICE QUESTIONS
(f) Boiling removes the ..........--...-+.:02+
1. Two gases dissolved in natural water are
hardness of water.
(a) oxygen and carbon dioxide
(g) Water turns the colour of anhydrous (b) hydrogen and oxygen
copper Sulphate ..........:c..ss00e (c) sulphur dioxide and hydrogen
(h) Water gas is a mixture Of ......... ese (d) chlorine and ammonia
NN fers :
ee ateecsadeacvan The sticky substance formed when soap is added
State whether the reasons given in column to hard water is
B correctly explain the statements given in (a) scum (b) lather
columnA (c) residue (d) precipitate
Column A Column B Temporary hardness of water can be removed
tad

(a) Acid is added to To make it alkaline by

water before it is (a) filtering (b) boiling
electrolysed. (c) loading (d) none of the above
(b) Alcohol is mixed Because it lowers
Water is sterilized by
with the water used the freezing point oxygen gas
(a) nitrogen gas (b)
in car radiators of water (d) hydrogen gas
(c) chlorine gas
(c) Icebergs float in Because ice is not
The ultimate source of all water on the earth is
ocean water a Saline substance
(d) Carbonated drinks Because the (a) oceans and seas
are bottled under solubility of (b) spring and wells
high pressure carbon dioxide (c) rivers and lakes
increases with
(d) rain
pressure.

“PROJECT ACTIVITIES }—— z =

- Organize a poster competition in your school for importance of water resources. Also
en

sal ize, a campaign to conserve water

— —_
a

Downloaded from https:// www. studiestoday.com