Selina Textbook Solutions: Water | Chemistry Class 6 ICSE PDF Download

 Page 1


POINTS TO REMEMBER 
1. Water cannot be replanished and without water we cannot live. 
2. 4 / 5 th of earth’s surface is covered with water and 1% of this available water is in 
the form of rivers, lakes, ponds and under ground water. It is utilized for agriculture 
and living beings consumption. 
3. In the atmosphere water is present in the form of vapour, mist, clouds etc. 
 
4. Distillation : The process of removal of the dissolved salts from sea/ocean water. 
5. Purest form of water is rain water as it is formed by evaporation and condensation. 
6. Sea water is unfit for agriculture as plants do not tolerate saline water. 
7. Change of water from water bodies (lakes, rivers and oceans) into vapours in air 
and condensing of vapours and fall in the form of snow, water is called water cycle 
and water cycle plays an important role in 
(i) restoring the lost water from earth’s surface 
(ii) in controlling the climatic conditions. 
8. Water vapour is one of the invisible gases which makes up the air we breathe. 
9. Drinking water may contain some minerals and salts but it must be free from 
suspended impurities, harmful bacteria and germs. 
10. Sometimes water from a source look clear but may contain germs which cause 
water borne diseases like typhoid, cholera, jaundice, dysentry, gastroenteritis etc. 
11. Water can be made fit for drinking by 
(i) boiling, 
(ii) sterilisation 
(iii) exposing to air and sunlight 
(iv) by chemical treatment like chlorination or ozonisation. 
12. Water is universal solvent i.e. water can dissolve nearly in every substance. 
13. Distilled water is the purest form of water but not good for drinking purposes. It is 
good for medicinal purposes, laboratories and batteries. 
14. Both stirring and heating help in dissolving the substance in water. 
15. “The amount of solute that dissolves in a given quantity of solvent at a given 
temperature is called solubility of the solute.” 
16. Air dissolved in water helps aquatic animals and plants to survive. 
17. Eutrophication: “The deficiency of oxygen in the water may cause death of 
aquatic animals. This loss of dissolved oxygen from water in water bodies is called 
eutrophication.” 
Page 2


POINTS TO REMEMBER 
1. Water cannot be replanished and without water we cannot live. 
2. 4 / 5 th of earth’s surface is covered with water and 1% of this available water is in 
the form of rivers, lakes, ponds and under ground water. It is utilized for agriculture 
and living beings consumption. 
3. In the atmosphere water is present in the form of vapour, mist, clouds etc. 
 
4. Distillation : The process of removal of the dissolved salts from sea/ocean water. 
5. Purest form of water is rain water as it is formed by evaporation and condensation. 
6. Sea water is unfit for agriculture as plants do not tolerate saline water. 
7. Change of water from water bodies (lakes, rivers and oceans) into vapours in air 
and condensing of vapours and fall in the form of snow, water is called water cycle 
and water cycle plays an important role in 
(i) restoring the lost water from earth’s surface 
(ii) in controlling the climatic conditions. 
8. Water vapour is one of the invisible gases which makes up the air we breathe. 
9. Drinking water may contain some minerals and salts but it must be free from 
suspended impurities, harmful bacteria and germs. 
10. Sometimes water from a source look clear but may contain germs which cause 
water borne diseases like typhoid, cholera, jaundice, dysentry, gastroenteritis etc. 
11. Water can be made fit for drinking by 
(i) boiling, 
(ii) sterilisation 
(iii) exposing to air and sunlight 
(iv) by chemical treatment like chlorination or ozonisation. 
12. Water is universal solvent i.e. water can dissolve nearly in every substance. 
13. Distilled water is the purest form of water but not good for drinking purposes. It is 
good for medicinal purposes, laboratories and batteries. 
14. Both stirring and heating help in dissolving the substance in water. 
15. “The amount of solute that dissolves in a given quantity of solvent at a given 
temperature is called solubility of the solute.” 
16. Air dissolved in water helps aquatic animals and plants to survive. 
17. Eutrophication: “The deficiency of oxygen in the water may cause death of 
aquatic animals. This loss of dissolved oxygen from water in water bodies is called 
eutrophication.” 
EXERCISE-I 
Question 1. 
Name: 
(a) Three major sources of natural water 
(b) Four sources of surface water. 
(c) Two underground sources of water. 
Answer: 
(a) Three major sources of natural water : 
1. Surface water (sea water) 
2. Above surface water (rain) 
3. 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 ? 
Answer: 
Page 3


POINTS TO REMEMBER 
1. Water cannot be replanished and without water we cannot live. 
2. 4 / 5 th of earth’s surface is covered with water and 1% of this available water is in 
the form of rivers, lakes, ponds and under ground water. It is utilized for agriculture 
and living beings consumption. 
3. In the atmosphere water is present in the form of vapour, mist, clouds etc. 
 
4. Distillation : The process of removal of the dissolved salts from sea/ocean water. 
5. Purest form of water is rain water as it is formed by evaporation and condensation. 
6. Sea water is unfit for agriculture as plants do not tolerate saline water. 
7. Change of water from water bodies (lakes, rivers and oceans) into vapours in air 
and condensing of vapours and fall in the form of snow, water is called water cycle 
and water cycle plays an important role in 
(i) restoring the lost water from earth’s surface 
(ii) in controlling the climatic conditions. 
8. Water vapour is one of the invisible gases which makes up the air we breathe. 
9. Drinking water may contain some minerals and salts but it must be free from 
suspended impurities, harmful bacteria and germs. 
10. Sometimes water from a source look clear but may contain germs which cause 
water borne diseases like typhoid, cholera, jaundice, dysentry, gastroenteritis etc. 
11. Water can be made fit for drinking by 
(i) boiling, 
(ii) sterilisation 
(iii) exposing to air and sunlight 
(iv) by chemical treatment like chlorination or ozonisation. 
12. Water is universal solvent i.e. water can dissolve nearly in every substance. 
13. Distilled water is the purest form of water but not good for drinking purposes. It is 
good for medicinal purposes, laboratories and batteries. 
14. Both stirring and heating help in dissolving the substance in water. 
15. “The amount of solute that dissolves in a given quantity of solvent at a given 
temperature is called solubility of the solute.” 
16. Air dissolved in water helps aquatic animals and plants to survive. 
17. Eutrophication: “The deficiency of oxygen in the water may cause death of 
aquatic animals. This loss of dissolved oxygen from water in water bodies is called 
eutrophication.” 
EXERCISE-I 
Question 1. 
Name: 
(a) Three major sources of natural water 
(b) Four sources of surface water. 
(c) Two underground sources of water. 
Answer: 
(a) Three major sources of natural water : 
1. Surface water (sea water) 
2. Above surface water (rain) 
3. 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 ? 
Answer: 
(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. 
Answer: 
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 
(d) Bread 
(e) Water melon 
Answer: 
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% 
Page 4


POINTS TO REMEMBER 
1. Water cannot be replanished and without water we cannot live. 
2. 4 / 5 th of earth’s surface is covered with water and 1% of this available water is in 
the form of rivers, lakes, ponds and under ground water. It is utilized for agriculture 
and living beings consumption. 
3. In the atmosphere water is present in the form of vapour, mist, clouds etc. 
 
4. Distillation : The process of removal of the dissolved salts from sea/ocean water. 
5. Purest form of water is rain water as it is formed by evaporation and condensation. 
6. Sea water is unfit for agriculture as plants do not tolerate saline water. 
7. Change of water from water bodies (lakes, rivers and oceans) into vapours in air 
and condensing of vapours and fall in the form of snow, water is called water cycle 
and water cycle plays an important role in 
(i) restoring the lost water from earth’s surface 
(ii) in controlling the climatic conditions. 
8. Water vapour is one of the invisible gases which makes up the air we breathe. 
9. Drinking water may contain some minerals and salts but it must be free from 
suspended impurities, harmful bacteria and germs. 
10. Sometimes water from a source look clear but may contain germs which cause 
water borne diseases like typhoid, cholera, jaundice, dysentry, gastroenteritis etc. 
11. Water can be made fit for drinking by 
(i) boiling, 
(ii) sterilisation 
(iii) exposing to air and sunlight 
(iv) by chemical treatment like chlorination or ozonisation. 
12. Water is universal solvent i.e. water can dissolve nearly in every substance. 
13. Distilled water is the purest form of water but not good for drinking purposes. It is 
good for medicinal purposes, laboratories and batteries. 
14. Both stirring and heating help in dissolving the substance in water. 
15. “The amount of solute that dissolves in a given quantity of solvent at a given 
temperature is called solubility of the solute.” 
16. Air dissolved in water helps aquatic animals and plants to survive. 
17. Eutrophication: “The deficiency of oxygen in the water may cause death of 
aquatic animals. This loss of dissolved oxygen from water in water bodies is called 
eutrophication.” 
EXERCISE-I 
Question 1. 
Name: 
(a) Three major sources of natural water 
(b) Four sources of surface water. 
(c) Two underground sources of water. 
Answer: 
(a) Three major sources of natural water : 
1. Surface water (sea water) 
2. Above surface water (rain) 
3. 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 ? 
Answer: 
(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. 
Answer: 
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 
(d) Bread 
(e) Water melon 
Answer: 
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% 
Question 5. 
What are the three states of water ? 
Answer: 
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 ? 
Answer: 
Ice, liquid water and steam have same composition i.e. 2 parts hydrogen and one part 
oxygen by volume and same formula H 2O, can be easily transformed from one state to 
other by heating or cooling. 
Question 7. 
How is a cloud formed ? 
Answer: 
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 ? 
Answer: 
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 
Answer: 
Page 5


POINTS TO REMEMBER 
1. Water cannot be replanished and without water we cannot live. 
2. 4 / 5 th of earth’s surface is covered with water and 1% of this available water is in 
the form of rivers, lakes, ponds and under ground water. It is utilized for agriculture 
and living beings consumption. 
3. In the atmosphere water is present in the form of vapour, mist, clouds etc. 
 
4. Distillation : The process of removal of the dissolved salts from sea/ocean water. 
5. Purest form of water is rain water as it is formed by evaporation and condensation. 
6. Sea water is unfit for agriculture as plants do not tolerate saline water. 
7. Change of water from water bodies (lakes, rivers and oceans) into vapours in air 
and condensing of vapours and fall in the form of snow, water is called water cycle 
and water cycle plays an important role in 
(i) restoring the lost water from earth’s surface 
(ii) in controlling the climatic conditions. 
8. Water vapour is one of the invisible gases which makes up the air we breathe. 
9. Drinking water may contain some minerals and salts but it must be free from 
suspended impurities, harmful bacteria and germs. 
10. Sometimes water from a source look clear but may contain germs which cause 
water borne diseases like typhoid, cholera, jaundice, dysentry, gastroenteritis etc. 
11. Water can be made fit for drinking by 
(i) boiling, 
(ii) sterilisation 
(iii) exposing to air and sunlight 
(iv) by chemical treatment like chlorination or ozonisation. 
12. Water is universal solvent i.e. water can dissolve nearly in every substance. 
13. Distilled water is the purest form of water but not good for drinking purposes. It is 
good for medicinal purposes, laboratories and batteries. 
14. Both stirring and heating help in dissolving the substance in water. 
15. “The amount of solute that dissolves in a given quantity of solvent at a given 
temperature is called solubility of the solute.” 
16. Air dissolved in water helps aquatic animals and plants to survive. 
17. Eutrophication: “The deficiency of oxygen in the water may cause death of 
aquatic animals. This loss of dissolved oxygen from water in water bodies is called 
eutrophication.” 
EXERCISE-I 
Question 1. 
Name: 
(a) Three major sources of natural water 
(b) Four sources of surface water. 
(c) Two underground sources of water. 
Answer: 
(a) Three major sources of natural water : 
1. Surface water (sea water) 
2. Above surface water (rain) 
3. 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 ? 
Answer: 
(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. 
Answer: 
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 
(d) Bread 
(e) Water melon 
Answer: 
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% 
Question 5. 
What are the three states of water ? 
Answer: 
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 ? 
Answer: 
Ice, liquid water and steam have same composition i.e. 2 parts hydrogen and one part 
oxygen by volume and same formula H 2O, can be easily transformed from one state to 
other by heating or cooling. 
Question 7. 
How is a cloud formed ? 
Answer: 
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 ? 
Answer: 
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 
Answer: 
(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 
Question 1. 
Name: 
(a) Two chemicals used to destroy germs present in water. 
(b) Two diseases which spread through impure water. 
(C) A chemical used for loading. 
(d) Two substances which add taste to water. 
(e) Two household methods to get safe drinking water. 
Answer: 
(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. 
Answer in brief: 
(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?