Water

MULTIPLE CHOICE QUESTIONS:

1.Water content in human body is
70% 75% 80% 90%
2. The purest form of natural water is
Seawater river water rainwater lake water
3. When the water vapour changes into tiny droplets of water near the ground, it is called
Mist dew fog frost
4. Water is a
Compound element mixture none of the above
5. Which of the following is the source of underground water?
Lakes Springs Rivers Ponds
6. Under normal conditions, water exists as a
Solid liquid gas all of the above
7. The most suitable source of water for domestic and industrial uses is
Sea water River water Spring water rainwater
8. Common salt is obtained from sea water by
Distillation crystallisation evaporation sublimation
9. The substance which is insoluble in water is
Sugar salt chalk sodium carbonate
10. A substance in which another substance is dissolved to form a solution is called
Solute solvent precipitate none of the above
11. The most frequently used solvent is
Water alcohol vinegar carbon disulphide
12. The substance which gets dissolved in a solvent to form a solution is called
Solute residue sediment sublimate
13. The solubility of a solute in solvent –
Increases by stirring increase by heating
Depends upon the size of the solute particles all of the above
14. Chlorination of water is done
to kill the germs to remove the suspended impurities
to remove the dissolved impurities none of the above
15. A method used to kill harmful germs present in water is
Sedimentation Decantation Boiling filtration
16. Sea water is not fit for drinking because it contains a large amount of
Suspended impurities sugar dissolved salts none of the above
17. The gas which adds taste to water is
Oxygen Nitrogen Hydrogen Carbon dioxide
18. Distilled water is
Salty sweet sour tasteless
19. Which of the following is a water borne disease
Influenza typhoid Covid 19 Malaria
20. Water pollution is caused due to the addition:
Domestic sewage pesticides effluents all of the above
21. One of the methods to control water pollution is
Using synthetic detergents passing wastewater through effluent and sewage treatment plants
Washing clothes and utensils near water bodies using more fertilizers, pesticides etc.
22 Excess rainfalls may cause:
Floods droughts soil erosion both (a) &(c)
23. Conservation of water can be done by:
Rain water harvesting planting trees and plants
Avoiding misuse of water all of the above
Fill in the blanks:
(a) Water is a universal solvent.
(b) Rainwater is the purest form of natural water.
(c) Sand and dust are suspended impurities in water.
(d) Sea water has high concentration of salt (impurity).
(e) Water covers nearly 4 / 5 th of the surface of the earth.
(f) Evaporation of rain water leaves NO residue.
(g) Potash alum is the chemical added to water to remove the tiny suspended particles.
(h) A solution is a uniform mixture of a solute and a solvent.
(i) Ice, water and steam have different physical states but are chemically identical.
(j) Boiling kills most of the germs in water.
(k) The elements present in the molecules of water are hydrogen and oxygen.
Write True or False for the following statements
(a) Water is an element. False
(b) Alum is commonly used for removing suspended impurities. False
(c) Tap water does not contain dissolved impurities. False
(d) Distillation is a good method for purifying water for town supply. False
Match the following:
Column A Column B
A solution in which more solute can be dissolved. Solution
A medium in which a substance dissolves Unsaturated solution
A homogeneous mixture Solvent
Short Answer:
1.What are the three states of water?
Ans: Three states of water are: Ice (solid), Liquid (water), Gaseous (steam)
2. Name:(a) Three major sources of natural water
Ans: Three major sources of natural water are: Surface water (sea water), Above surface water (rain), Underground water
(springs)
(b) Four sources of surface water.
Ans: Four sources of surface water sources are: Ocean water, River water, Lake water, Glaciers
(c) Two underground sources of water.
Ans: Two sources of underground water: Well water, Spring water
3. List three major impurities present in river water.
Ans: Three major impurities present in river water are: Suspended impurities like clay and sand particles, Harmful bacteria,
Mineral salts.
4. Answer the following questions in short:
(a) In which form is water present in the atmosphere?
Water is present in the form of water vapours in the atmosphere.
(b) Which source of water contains the highest concentration of salt in it?
Sea water contains highest concentration of salt.
(c) What possible impurities does rain water contain?
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.
(d) What is water table?
Level of ground water is called water table.
5. Find the percentage of water in the following:
Ans: Percentage of water in:
(a) Rice — 3 % to 4% Wheat grain — 3% to 4% (b) Eggs —75% (c) Tomatoes — 95%
(d) Bread —25% (e) Water melon — 97%
6. Define:
Ans: (a) Solute: A solute is a substance that dissolves in a medium which can be water or any other substance. Solute is in
smaller quantity in a solution.
(b) Solvent: A solvent is a medium in which a solute dissolves. It is in large quantity in a solution. Water is the most common
solvent. The other solvents are alcohol, carbon tetrachloride etc.
(c) Solution: A solution is a homogeneous uniform mixture formed by a solute and a solvent.
(d) Saturated solution: When a solution cannot dissolve any more of solute at a given temperature, it is called saturated
solution.
(e) Unsaturated solution: A solution that can take up more of the solute at a given temperature, is said to be an unsaturated
solution.
7. Why is water called a universal solvent?
Ans: As water can dissolve in most of the substances, solids, liquid and gaseous. Therefore, it is called universal solvent.
8. Name:
(a) Two chemicals used to destroy germs present in water: Chlorine, Potassium permanganate, sterilizing water with ozone.
(b) Two diseases which spread through impure water: cholera, dysentery.
(c) A Chemical used for loading: potash alum.
(d) Two substance which ad taste to water: Minerals and carbon dioxide gas
(e) Methods to get safe drinking water: Adding chlorine tablets, by adding potassium permanganate crystals.
9. Define:
(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 under pressure is blown into the filtered water.
This process is called aeration.
10. Answer in brief:
(a) Why is river water unfit for drinking?
River water contains mineral salts, suspended impurities like clay, sand particles, organic matter and bacteria and is not fit
for drinking.
(b) Why is tap water a mixture?
Tap water contains, minerals, air, chlorine and other dissolved impurities that varies from place to place, therefore it is a
mixture.
(c) What is mineral water?
Mineral water is pure water fit for drinking. It is collected from natural source and contains air, minerals and salts free from
suspended impurities, harmful bacteria and germs.
(d) What is the purpose of adding bleaching powder to water supplied to the town?
Adding bleaching powder to water, kills germs and harmful bacteria and viruses present in water.
(e) How is chemically pure water obtained in the laboratory?
Chemically pure water for laboratories is obtained-by distillation. Distilled water does not contain any salt or mineral
(f) how is water in swimming pool kept free a germ?
Water in swimming pool kept free from infections and germs by chlorination i.e. treating water with chlorine gas.
Long Answers:
1.What is water cycle? What is its importance?
Ans: 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:
It assures a continuous supply of water to us.
In controlling the climatic conditions all over the world.
2. Give reasons:
(a) Rain water considered the purest form of natural water?
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.
(b) Spring water pure enough for drinking but unsuitable for laboratory use?
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
(c)The taste of spring water differs at different places?
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.
(d) Ice, liquid water and steam considered to have the same chemical composition
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.
3. How are the following formed?
Ans: (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.
4. State two factors by which solubility of a solute in a solvent can be increased.
Ans: Two factors are: Stirring, Increase in temperature.
5. Name the steps involved in the purification of drinking water supplied in cities and towns.
Ans: 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:
Loading and sedimentation: to settle the suspended impurities to form a sediment for this purpose potash alum is added.
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 submersible pumps which have filters fitted in them. This clear water still
contains germs.
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.
6. Give reasons:
(a) Ice floats on water.
Water has maximum density at 4°C. Ice is lighter than water therefore it floats on water.
(b) Marine life is able to survive in colder regions.
This anomalous property of water enables aquatic plants and animals to survive in colder regions of world because even
when the water of ponds, lakes, river freezes it freezes on the top but remains a liquid below ice layer.
(c) Water droplets can be seen outside a chilled water bottle.
Sometimes we see water droplets on the outer surface of the glass containing ice-cold water, this is because the water
vapour presents in ‘air, on coming in contact with the cold glass of water, loses energy and gets converted into liquid state,
which we see as water droplets.
7. What is potable water? List four characteristics of potable water.
Ans: Potable water: Water fit for drinking purposes is called potable water.
Four characters of drinking water:
 It should be transparent.
 Should have no colour, no odour.
 Should be free from harmful bacteria and germs.
 It should contain same salts and minerals needed by the body CO2 to add to taste.
8. What are the three methods of removing germs from natural water. Explain.
Ans: Three methods to remove germs:
By boiling: Boiling kills germs present in water.
Adding potassium permanganate: By adding potassium permanganate in the well the germs can be killed.
Chlorination: After filtration water is passed through chlorination tank here chlorine kills the germs.
9. What are the three main causes of water pollution?
Ans: Three main causes of water pollution:
 Addition of waste products from homes.
 Addition of waste products from agriculture.
 Addition of waste from industries.
 Addition of sewage in water bodies.
10. State the main steps to be taken to prevent water pollution.
Ans: Steps to be taken to prevent water pollution:
 Trees and plants be planted along the banks of rivers and canals.
 Bathing and cleaning of animals near or in water sources be not allowed.
 Use of pesticides, insecticides, fungicides and fertilisers should be reduced.
 The polluted water from industries should be treated first and then discharged into water bodies.
 Use biodegradable detergents.
 Water containing sewage should be passed through sewage treatment plants first and then this water should be
used for irrigation.
 Wells should be covered properly and washing and cleaning of clothes, utensils and animals should not be done
near the well to keep them clean.
11. State four ways by which water can be conserved.
Ans: Five ways to conserve water:
 Do not allow water to drip from defective taps.
 More dams should be built.
 More plantation should be done as plants help in bringing rain.
 Wastage of water should be avoided.
 Close the tap when you are brushing your teeth. Rather use a mug. Close the tap when you are washing clothes,
open the tap only when you need it. Reduce, Reuse and recycle should be our mantra
12. State some of the ways in which you as an individual can conserve water.
Ans: The ways in which we can conserve water are as follows:
 Use a bucket for taking it.
 Make sure, water does not overflow from overhead tanks of your house.
 Close the tap when you are brushing your teeth.
 Wash fruits, vegetable in a bowl of water, rather than under a running tap. Water used for washing vegetables may
be used to water plants in the garden.