Water ICSE Class-6th Concise Selina Chemistry Solutions Chapter-7. We Provide Step by Step Answer of Objective, True False , Fill in the blanks , Match the following , Short/Long Answer Type of Exercise-7 Water. Visit official Website  for detail information about ICSE Board Class-6.

## Water ICSE Class-6th Concise Selina Chemistry Solutions Chapter-7

### EXERCISE-I

#### Question 1.

Name:

(a) Three major sources of natural water
(b) Four sources of surface water.
(c) Two underground sources of water.

(a) Three major sources of natural water :

Surface water (sea water)
Above surface water (rain)
Underground water (springs)

(b) Four sources of surface water sources :

1. Ocean water
2. River water
3. Lake water
4. Glaciers

(c) Two sources of underground water :

1. Well water
2. Spring water

#### Question 2.

Answer the following questions in short:

(a) In which form is water present in the atmosphere ?
(b) Which source of water contains the highest concentration of salt in it ?
(c) Why is rain water considered the purest form of natural water?
(d) What possible impurities does rain water contain ?
(e) What is water table ?
(f) Why is spring water pure enough for drinking but unsuitable for laboratory use ?
(g) Why the taste of spring water differs at different places ?

(a) Water is present in the form of water vapours in the atmosphere.
(b) Sea water contains highest concentration of salt.
(c) Rain water is the purest form of water as it is distilled water i.e. water from surface of earth has evaporated and then vapours condense in the atmosphere.
(d) The impurities present in rain water are dust and dissolved gases like oxygen, nitrogen and carbon dioxide and these gases are not poisonous, rain water is safe for drinking.
(e) Level of ground water is called water table.
(f) Spring water is free from suspended impurities and germs (harmful bacteria) as water has been filtered through different layers of soil and is fit for drinking. Spring water contains dissolved impurities which are due to the nature of soil surrounding the spring and cannot be used for laboratory purposes, where distilled water free from impurities is needed.

(g) Spring water contains unsolved impurities which have entered the water from surrounding soil and soil impurities (salts) differ from place to place. Hence taste of water differs from place to place.

#### Question 3.

List three major impurities present in river water.
Three major impurities present in river water :

1. Suspended impurities like clay and sand particles.
2. Harmful bacteria.
3. Mineral salts.

#### Question 4.

Give the percentage of water in the following :

(a) Rice and wheat grains
(b) Eggs
(c) Tomatoes
(e) Water melon

Percentage of water in :

(a) Rice — 3 % to 4% Wheat grain — 3% to 4%
(b) Eggs —75%
(c) Tomatoes — 95%
(e) Water melon — 97%

#### Question 5.

What are the three states of water ?

Three states of water are :

1. Ice (solid)
2. Liquid (water)
3. Gaseous (steam)

#### Question 6.

Why are ice, liquid water and steam considered to have the same chemical substance ?

Ice, liquid water and steam have same composition i.e. 2 parts hydrogen and one part oxygen by volume and same formula H2O, can be easily transformed from one state to other by heating or cooling.

#### Question 7.

How is a cloud formed ?
Water from the surface of earth, lakes, seas, rivers, formed by plants (transpiration) etc. evaporates and rises high up in the atmosphere and condense into water droplets and collect to form cloud.

#### Question 7.

How is a cloud formed ?
Water from the surface of earth, lakes, seas, rivers, formed by plants (transpiration) etc. evaporates and rises high up in the atmosphere and condense into water droplets and collect to form cloud.

#### Question 8.

What is water cycle ? What is its importance ?
Water cycle : The change of water from one form to another in nature which results in continuous circulation of water from earth’s surface to the atmosphere and from the atmosphere back to the earth’s surface is called water cycle.
Importance of water cycle:

1. It assures a continuous supply of water to us.
2. In controlling the climatic conditions all over the world.

#### Question 9.

How are the following formed ?

(a) fog
(b) mist
(c) dew
(d) frost

(a) Fog : When water vapours change into tiny droplets of water near the ground, fog is formed.
(b) Mist: When tiny droplets of water remain suspended in air it is called mist.
(c) Dew : When the water vapour condenses on cold objects like grass, leaves and flowers in winter in the form of tiny droplets of water called dew.
(d) Frost: When the dew freezes it is called frost.

### EXERCISE-II

(Water ICSE Class-6th Concise Selina Solutions Chapter-7)

#### Question 1.

Name:

(a) Two chemicals used to destroy germs present in water.
(b) Two diseases which spread through impure water.
(d) Two substances which add taste to water.
(e) Two household methods to get safe drinking water.

(a) Two chemicals used to kill germs in water are:

1. Chlorine.
2. Potassium permanganate.
3. terilizing water with ozone.

(b) Two diseases are cholera, dysentry.
(c) Chemical used for loading is potash alum.
(d) Minerals and carbon dioxide gas adds taste to water.
(e) Methods to get safe drinking water:

1. Adding chlorine tablets.
2. By adding potassium permanganate crystals.

#### Question 2.

(a) Why is river water unfit for drinking?
(b) Why is tap water a mixture?
(c) What is mineral water?
(d) What is the purpose of adding bleaching powder to water supplied to the town?
(e) How is chemically pure water obtained in the laboratory?
(f) how is water in swimming pool kept free a germs?

(a) River water contains mineral salts, suspended impurities like clay, sand particles, organic matter and bacteria and is not fit for drinking.
(b) Tap water contains, minerals, air, chlorine and other dissolved impurities that varies from place to place, therefore it is a mixture.
(c) Mineral water is pure water fit for drinking. It is collected from natural source and contains air, minerals and salts free from suspended impuiities, harmful bacteria and germs.
(d) Adding bleaching powder to water, kills germs and harmful bacteria and viruses present in water.
(e) Chemically pure water for laboratories is obtained-by distillation. Distilled water does not contain any salt or mineral
(f) Water in swimming pool kept free from infections and germs by chlorination i.e. treating water with chlorine gas.

#### Question 3.

Define:

a) Sterilisation
(b) Sedimentation
(d) Aeration

(a) Sterilisation : The process of removal of microorganisms including bacterial spores from water to avoid water borne diseases is known as sterilisation.
(b) Sedimentation : The setting of suspended solid matter at the bottom of a liquid is called sedimentation.
(c) Loading : The process of adding a chemical to an impure liquid in order to increase the speed of sedimentation of suspended particles is called loading.
(d) Aeration : To kill harmful micro-organisms present in filtered water, air underpressure is blown into the filtered water. This process is called aeration.

#### Question 4.

What is potable water ? List four characteristics of potable water.
Potable water : Water fit for drinking purposes is called potable water.
Four characters of drinking water :

1. It should be transparent.
2. Should have no colour, no odour.
3. Should be free from harmful bacteria and germs.
4. It should contain same salts and minerals needed by the body CO2 to add to taste.

#### Question 5.

Why is water important for plants and animals ?

##### Importance of water for plants:
1. Plants need water to prepare their food, for germination and growth to produce fruits, flowers etc.
2. For conduction of food prepared by plants to other-parts of plant i.e., for translocation
3. Large number of plants live in water; water provides nutrients and oxygen for their survival.
Crops need water for their growth. Water in the form of rain, washes the dust and smoke deposited on leaves by vehicles and helps the stomata in exchanging gases.
##### Importance of water for animals:
1. Lot of water is lost by the body of animals by sweating, in the form of urine and evaporation while doing various activities, so to make up for the lost water animals consume a lot of water in the form of drinking.
2. Water keeps the animals fresh and is natural medicine for their many ailments.
3. And Water is good solvent and helps in the process of digestion, blood circulation, excretion etc. in the body of organisms.
4. Water is essential for the cleanliness of animals and their surroundings.

#### Question 6.

What are the three methods of removing germs from natural water. Explain.
Three methods to remove germs :

1. By boiling : Boiling kills germs present in water.
2. Adding potassium permaganate: By adding potassium permaganate in the well the germs can be killed.
3. Chlorination : After filtration water is passed through chlorination tank here chlorine kills the germs.

#### Question 7.

Name the steps involved in the purification of drinking water supplied in cities and towns.
The water source for our towns and cities are river, lakes or underground water which contains suspended and dissolved impurities.
To remove these impurities steps involved are :

1. Loading and sedimentation : to settle the suspended impurities to form a sediment for this purpose potash alum is added.
2. Filtration : The water still contains lighter suspended impurities which are removed by filtration through sand and gravel. In cities ground water is drawn from tube well or submurcible pumps which have filters fitted in them. This clear water still contains germs.
3. Chlorination : To kill germs water is passed into chlorination tank where it is treated with chlorine to kill germs.
Water is now potable i.e. safer for drinking and supplied to homes.

#### Question 8.

What is the taste of distilled water ? Why is it not potable?
Taste of water is tasteless i.e. flat. It is because distilled water does not contain any salt or mineral required for our body. So it is not potable water.

#### Question 9.

Give reasons :

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