Topics you will learn :

1. Introduction 6. Purification of Water 2. Water cycle 7. Water Pollution 3. Properties of Water 8. Steps to reduce water pollution 4. Anomalous Expansion of Water 9. Conservation of Water 5. Hardness of water & It’s types

Water is one of the most essential things for all of us. More than 70%

of the earth’s surface is covered with water, which lies in oceans , seas ,

rivers , lakes and polar regions. All living things are made up of cells ,

which mainly constitutes water.

We use water for our daily household work like drinking , bathing ,

washing clothes , cleaning , cooking etc. Life is not possible without water.

Water is very important for plants and animals. It plays an important role

in our body as it requires for digestion of food, transportation of food

components to varous organs. Water can dissolve many substances

therefore it is known as “Universal Solvent” (Solvent means the liquid

which dissolves other substances). A large part of water is used for

agriculture and industries.

Think :

What are the sources of water ? How is the balance of water maintained on

the earth ?

The main source of water is Rain. There are some other sources of water

which includes oceans, seas, rivers , lakes , ponds , springs , wells and

ground water.

The Balance of water on earth : For agricultural , industrial and household

purposes a huge amount of water is consumed. Although the total amount

of water on earth remains constant. How ? That is because of “Water

Cycle”.

Water

Water

The continuous flow of water from earth’s surface to atmosphere and

from atmosphere to earth’s surface is called water cycle.

Water evaporate in the form of water vapour from the water bodies into

the atmosphere. Water vapours condense on dust particles and form

clouds. The clouds becomes heavy due to the formation of water droplets

and finally they fall as rain or snow on the earth’s surface. A part of the the

rain water seeps into the soil and the rest flows into the rivers. On melting

the snow caps of the mountains changes to water and flows into the rivers,

which finally merge with seas and oceans. Thus water changes from one

form to another continuously. This cyclic change in the states of water is

called water cycle.

Properties of Water :

i) Pure water s odourless , colourless , tasteless.

ii) It is transparent.

iii) It is liquid at room temperature and normal pressure.

iv) It can exist in solid as well as gaseous form as ice and water vapour

respectively.

v) It has a maximum density at 40C. (1 g/cm3)

vi) Boiling point of water is 1000C and freezing point is 00C.

vii) It can dissolve most of the substances, so it is known as a Universal

solvent.

viii) Pure water does not conduct electricity.

Experiment 1 :

Aim : To determine the boiling point of pure water.

Aids : Round bottom flask , Thermometer , Bunsen burner , Wire gauze ,

Iron stand.

Method : Take some pure water in the round bottom flask. Set up the

apparatuses as shown in the figure. See to it that the bulb of the

thermometer is dipped in the water. Note the temperature on the

thermometer. Light the Bunsen burner and start heating the water.

Observation : When the temperature reaches 100 0C , water starts boiling.

Note that once the water begins to boil , the temperature remains same till

all the water changes to vapour.

Conclusion : The boiling point of pure water is 100 0C.

Experiment 2 :

Aim : To determine the freezing point of water

Aids : Beaker , Iron stand , thermometer , crushed ice.

Method : Take some crushed ice in the beaker. With the help of iron stand

carefully suspend the thermometer in the beaker so that the bulb of it

completely dip in the ice. Note the temperature on the thermometer.

Observation: The mercury level in the thermometer falls till the

temperature becomes constant at 0 0c.

Conclusion : The freezing point of pure water is 0 0c.

Experiment 3 :

Aim : To demonstrate that pure water is a bad conductor of electricity.

Aids : 6 valts battery , 2 carbon electrodes , wires , beaker , distilled water

Method : Fill the beaker with distilled water. Place two carbon electrodes

into the water. Connect the electrodes to the bulb using wires, as shown in

the figure. Does the bulb glow ?

Observation : The bulb does not glow.

Conclusion : Pure water does not conduct electricity i.e. pure water does

not allow electricity to pass through it.

ANOMALOUS EXPANSION OF WATER :

Most of the substances expand on heating and contract on cooling. But

water shows opposite behavior between 4 0c to 0 0c. On cooling, water

contracts till it reaches a temperature of 4 0c and then starts expanding till

it reaches 0 0c. This abnormal expansion of water from 4 0c to 0 0c is

known as Anomalous Expansion of water.

Therefore, the volume of ice at 0 0c is more than the volume of water at 4 0c. This results the minimum density of ice at 0 0c. Thus ice being lighter

than water float on it and forms an insulating layer which keeps the

underlying water warm. Thus the aquatic animals are able to survive in it.

Hardness of Water :

We use soap along with water for washing clothes. Water when treated with soap, may or may not form lather (a frothy mass of bubbles / foam).

The water which lathers readily with soap is called SOFT water.

The water which does not lathers readily with soap is called HARD water.

Did you know ?

The colour of water in lakes and oceans appear to be bluish green.

This is due to three reasons -partial reflection of the sky , light scattering effect of the small suspended particles present in it and the presence of green algae and weeds.

Difference between Hard water and Soft water :

Hard water Soft water

It does not lather easily with soap. It lathers easily with soap.

Salts of calcium and magnesium are

present in it.

Salts of calcium and magnesium are

not present. Sodium salts may

present.

It is less pure. Compared to hard water it is more

pure.

Examples : Well water and Sea

water

Examples : Rain water and Distilled

water

What causes hardness of water ?

Water is a very good solvent. When water flows in rivers , seas and also

under the ground like in wells, it dissolves the salts of calcium and

magnesium present in rocks and soil. These dissolved salts are responsible

for the hardness of water.

Following salts of Calcium and Magnesium can cause hardness of water:

Calcium sulphate-CaSO4 , Calcium bicarbonate-Ca(HCO3)2 , Calcium

chloride-CaCl2 , Magnesium sulphate-MgSO4 , Magnesium bicarbonate-

Mg(HCO3)2 and Magnesium chloride - MgCl2

Types of Hardness :

There are two types of hardness of water. Temporary hardness of water

and Permanent hardness of water.

Hardness of water caused due to the presence of calcium and magnesium

bicarbonates is called Temporary hardness of water. It can be removed by

boiling of water. When water is boiled, the bicarbonates of calcium and

magnesium decompose to form carbonates.

Ca(HCO3)2 CaCO3 + CO2 + H2O

Mg(HCO3)2 MgCO3 + CO2 + H2O

Hardness of water caused due to the presence of sulphates and chlorides

of calcium and magnesium is called Permanent hardness of water.

For removing permanent hardness of water washing soda (sodium

carbonate) is used as it is cheap and easily available. Washing soda reacts

with calcium and magnesium salts present in hard water to form

carbonates of calcium and magnesium as prepitates, which can be removed

by filtration.

CaSO4 + Na2CO3 CaCO3 + Na2SO4

MgSO4 + Na2CO3 MgCO3 + Na2SO4

CaCl2 + Na2CO3 CaCO3 + 2NaCl

MgCl2 + Na2CO3 MgCO3 + 2NaCl

Why is it necessary to soften water ?

Due to the following reasons it is necessary to soften water.

Hard water is unfit for most of the domestic and industrial uses.

It consumes lot of soap and leaves dirty stains on clothes.

It causes skin irritation due to salts present in it.

Hard foodstuffs like pulses are difficult to cook in hard water.

When used for industrial purpose mainly in boilers, hard water

produces white deposites of insoluble substances called scales. The

scales mainly consists of CaCO3 , MgCO3 and CaSO4. They deposit on

the walls of boilers and do not allow proper conduction of heat,

which may lead to serious accidents like explosion of boilers.

What is Potable water ?

Water which is fit for drinking is called Potable water.

Purification of Water :

Water that we get in our homes usually comes from rivers or lakes. But

river water or lake water contains many impurities, suspended particles

and germs. These have to be removed from water before it is supplied to

our homes for drinking.

Following steps are taken to purify water in waterworks.

1. Sedimentation : After the water is pumped out from the river or lake

it is passed through a large sedimentation tanks. Here the water is

kept undisturbed for some hours. Most of the insoluble solid

impurities settle down at the bottom of the tank. Some alum can also

be added which helps the suspended particles to settle down fast.

2. Filtration : The water is then allowed to flow in another tank which

contains layers sand and gravel. This removes fine particles of

impurities.

3. Chlorination : Finally the water from the filtration tank is directed to

the chlorination tank where certain amount of chlorine gas is passed

in water. This process kills germs present in water. The clean water is

then supplied to different parts of the city through pipelines.

How do we clean water at home ?

At homes we use different methods such as Boiling , Filtration and Chlorination and UV-radiation.

Boiling water for 15 minutes kill all the germs present in it. Then the water is filtered and used.

Ceramic candle filters have minute pores which allow only water to pass through it, suspended particles are caught in the filters. Thus we can get potable water.

Nowadays, domestic water purifiers use UV-technique to make water germ

free. For example- Aquaguard is a such type of water purifier.

Above technique purify water in three stages.

1. Water from enters the purifier, here it is filtered through a ceramic /

porcelain candle which allows only water to pass through it, fine

particles are caught in the filter.

2. Then it is passed through activated charcoal (carbon) which makes

water colourless and odourless.

3. Then filtered water is passed from ultraviolet section, where UV lamp

radiates high-energy rays which kill germs.

WATER POLLUTION :

Did you know ? - Distilled water is not fit for drinking.

Distilled water is the purest form of water although it is not fit for drinking

because it is tasteless and doesn’t contain essential salts required for our

body.

The mixing of harmful substances like sewage , toxic chemicals from

industries , animal wastes , human wastes , etc in water is called Water

pollution. Polluted water contains many disease causing germs. Some

water borne diseases are : Cholera , Dysentery , Diarrhoes , Typhoid ,

Gastroenteritis and Hepatitis (Jaundice).

Following are some of the causes of water pollution :

1. Domestic wastes and Sewage are the major cause of water pollution. This includes washing clothes , bathing , cleaning animals in water bodies. Due to this many harmful germs enter water and causes waterborne diseases.

2. Many factories release toxic chemicals in the water boies, which pollute the water and affects aquatic animals.

3. Farmers use fertilizers , pesticides and insecticides to improve soil fertility. They contain harmful chemicals which are carried away into water bodies by the rain water.

4. Urinating and defecating near water bodies pollute the water which cause many diseases.

Steps to Reduce Water Pollution :

1. Sewage from homes, factories, hospitals, offices etc. should be treated

properly before discharging it into water bodies.

2. People should not bathe , wash clothes and clean utensils in water

bodies. Also cleaning of animals in water bodies should be stopped.

3. Farmers should use appropriate amount of fertilizers. Excessive use

of that should be avoided.

4. Toxic wastes released from the factories should be treated to remove

harmful chemicals before discharging them into water bodies.

5. Awareness should be spread among people in rural and slum areas to

stop water pollution. They should be made aware of the diseases

caused by polluted water.

CONVERSATION OF WATER

Population of the world is increasing day by day and so is the

demand of water. Therefore we all must use water economically and

wisely. Here are some of the ways to conserve water.

Turn off the tap when water is not in use. Leaky tapes and piles must

be repaired immediately.

You can shorten your shower, which saves lot of water.

After washing vegetables and fruits , reuse water for the plants.

Do not waste water while watering the plants in the garden/homes.

Rain Water Harvesting and Drip Irrigation are some of the methods

to conserve water.

Spread awareness for saving water.

SOME INTERESTING FACTS ABOUT WATER

1. Over 1.5 billion people do not have access to clean , safe water.

2. Almost 4 million people die each year from water related diseases.

3. The average toilet uses 8 litres of clean water in a single flush.

4. It takes about 300 litres of water to make the paper for just one

Sunday newspaper.

5. Agriculture is responsible for about 70% of the world’s water usage.

Industrial usage is 22%.

6. 443 million school days are lost each year due to water related illness.

7. On average, women in Africa and Asia have to walk 3.7 miles to collect

water.

8. It takes up to 5000 litres of water to produce 1kg of rice.

9. 80% of all illness in the developing world comes from water born

diseases.

10. About 1.8 million child deaths a year are due to diarrhoea. Facts taken from : http://matadornetwork.com/change/40-shocking-facts-about-water/