Selina Textbook Solutions: Water | Chemistry Class 8 ICSE PDF Download

 Page 1


Water 
Points to Remember: 
• Water is the source of life for all living beings. 
• Water occurs in all the three states of matter i.e. ice, liquid water and water 
vapours. 
• Water found in nature (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. 
• Potable water should be free from suspended impurities and harmful germs. 
• Water is a compound, with the molecular formula is H2O. 
• The boiling point of water is 100°C and the freezing point is 0°C. 
• 0°C is also called tripple point, because water can exist in all its three states. 
• The specific heat of water is higher than that of any other liquid. It is used as a 
cooling agent. 
• Water has minimum volume and maximum density at 4°C. This is called 
anomalous behaviour of water. 
• Water is an universal solvent. The gases dissolved in water have biological 
importance. They enable aquatic life to sustain itself. 
• Water may be ‘hard or soft’. Hardness of water can be removed by boiling or by 
chemical treatment. 
• Water pollution is a serious problem. 
• Industrial and agriculture processes, nuclear and thermal plants pollute water. 
Exercise – I 
Question 1. 
Name the four main sources of water. 
Answer: 
(i) Oceans (ii) Seas 
(iii) Rivers (iv) Lakes 
Question 2. 
State the importance of water cycle in nature. 
Answer: 
(i) Water cycle helps in regulating weather on the earth. 
(ii) Water cycle makes water available in various forms on the earth. 
Question 3. 
Why is water very precious for all living beings ? 
Answer: 
Water is one of the most precious substances for the existence of life. Since life on the earth 
began in the oceans, and since no living thing can survive without water, it is rightly called the 
source of life. 
Page 2


Water 
Points to Remember: 
• Water is the source of life for all living beings. 
• Water occurs in all the three states of matter i.e. ice, liquid water and water 
vapours. 
• Water found in nature (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. 
• Potable water should be free from suspended impurities and harmful germs. 
• Water is a compound, with the molecular formula is H2O. 
• The boiling point of water is 100°C and the freezing point is 0°C. 
• 0°C is also called tripple point, because water can exist in all its three states. 
• The specific heat of water is higher than that of any other liquid. It is used as a 
cooling agent. 
• Water has minimum volume and maximum density at 4°C. This is called 
anomalous behaviour of water. 
• Water is an universal solvent. The gases dissolved in water have biological 
importance. They enable aquatic life to sustain itself. 
• Water may be ‘hard or soft’. Hardness of water can be removed by boiling or by 
chemical treatment. 
• Water pollution is a serious problem. 
• Industrial and agriculture processes, nuclear and thermal plants pollute water. 
Exercise – I 
Question 1. 
Name the four main sources of water. 
Answer: 
(i) Oceans (ii) Seas 
(iii) Rivers (iv) Lakes 
Question 2. 
State the importance of water cycle in nature. 
Answer: 
(i) Water cycle helps in regulating weather on the earth. 
(ii) Water cycle makes water available in various forms on the earth. 
Question 3. 
Why is water very precious for all living beings ? 
Answer: 
Water is one of the most precious substances for the existence of life. Since life on the earth 
began in the oceans, and since no living thing can survive without water, it is rightly called the 
source of life. 
Water forms a large part of the body mass of all living organisms — 90% of human blood is 
water. Water has the ability to dissolve a number of substances. Therefore, it serve as the liquid 
medium in which all reactions within the living body take place. 
Fruits and vegetables contain water in them. Even dry-looking substances like wood, peas, 
beans, grams, etc., contain some amount of water. 
Question 4. 
Name the two gases from which water is formed. What is the chemical composition of these two 
gases in water ? Give the molecular formula of water ? 
Answer: 
Oxygen and hydrogen 
Chemical composition = H2 and O2 proportion 2:1 
Molecular formula = H2O 
Question 5. 
What is the effect on boiling point of water when 
(a) pressure is increased 
(b) impurity is added 
Answer: 
(a) The boiling point of water increases with an increase, in pressure. 
(b) Any impurity present in water lowers its freezing point and raises its boiling point. 
For example, salt is added to ice to lower its melting point. Such a mixture is called a freezing-
mixture. The melting is called a freezing mixture is about -15° C. 
Question 6. 
Give reasons: 
(a) Water is used as a cooling agent 
(b) Water pipes burst in severe winters. 
(c) It is difficult to cook in hills compared to plains. 
(d) Ice floats on water. 
(e) Sea water does not freeze at 0°C. 
Answer: 
(a) Water has high specific heat. Water neither heats up nor cools down quickly. This property 
makes water as a excellent cooling agent. 
(b) Water pipes bursts in severe winter because the water inside I the pipes freezes and 
increases its volume. 
(c) Water boils at a lower temperature in the hills, where the atmospheric pressure is lower than 
in the plains. This is why it takes a longer time to cook in hilly regions. 
(d) Ice has low density as compared to water. Water has maximum density at 4°C. That is why 
ice floats on water. 
(e) There are impurities dissolved in sea water which increases the freezing point. That is why 
sea water does not freeze at 0°C. 
Question 7. 
How does anomalous expansion of water help aquatic organisms in cold climates ? 
Answer: 
The anomalous expansion of water helps in survivals of water animals in very cold climates. 
Initially when temperature of water falls, it becomes heavier and sinks down. This process 
continues till 4°C. Then after this expansion takes place. The surface layer of water gets 
Page 3


Water 
Points to Remember: 
• Water is the source of life for all living beings. 
• Water occurs in all the three states of matter i.e. ice, liquid water and water 
vapours. 
• Water found in nature (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. 
• Potable water should be free from suspended impurities and harmful germs. 
• Water is a compound, with the molecular formula is H2O. 
• The boiling point of water is 100°C and the freezing point is 0°C. 
• 0°C is also called tripple point, because water can exist in all its three states. 
• The specific heat of water is higher than that of any other liquid. It is used as a 
cooling agent. 
• Water has minimum volume and maximum density at 4°C. This is called 
anomalous behaviour of water. 
• Water is an universal solvent. The gases dissolved in water have biological 
importance. They enable aquatic life to sustain itself. 
• Water may be ‘hard or soft’. Hardness of water can be removed by boiling or by 
chemical treatment. 
• Water pollution is a serious problem. 
• Industrial and agriculture processes, nuclear and thermal plants pollute water. 
Exercise – I 
Question 1. 
Name the four main sources of water. 
Answer: 
(i) Oceans (ii) Seas 
(iii) Rivers (iv) Lakes 
Question 2. 
State the importance of water cycle in nature. 
Answer: 
(i) Water cycle helps in regulating weather on the earth. 
(ii) Water cycle makes water available in various forms on the earth. 
Question 3. 
Why is water very precious for all living beings ? 
Answer: 
Water is one of the most precious substances for the existence of life. Since life on the earth 
began in the oceans, and since no living thing can survive without water, it is rightly called the 
source of life. 
Water forms a large part of the body mass of all living organisms — 90% of human blood is 
water. Water has the ability to dissolve a number of substances. Therefore, it serve as the liquid 
medium in which all reactions within the living body take place. 
Fruits and vegetables contain water in them. Even dry-looking substances like wood, peas, 
beans, grams, etc., contain some amount of water. 
Question 4. 
Name the two gases from which water is formed. What is the chemical composition of these two 
gases in water ? Give the molecular formula of water ? 
Answer: 
Oxygen and hydrogen 
Chemical composition = H2 and O2 proportion 2:1 
Molecular formula = H2O 
Question 5. 
What is the effect on boiling point of water when 
(a) pressure is increased 
(b) impurity is added 
Answer: 
(a) The boiling point of water increases with an increase, in pressure. 
(b) Any impurity present in water lowers its freezing point and raises its boiling point. 
For example, salt is added to ice to lower its melting point. Such a mixture is called a freezing-
mixture. The melting is called a freezing mixture is about -15° C. 
Question 6. 
Give reasons: 
(a) Water is used as a cooling agent 
(b) Water pipes burst in severe winters. 
(c) It is difficult to cook in hills compared to plains. 
(d) Ice floats on water. 
(e) Sea water does not freeze at 0°C. 
Answer: 
(a) Water has high specific heat. Water neither heats up nor cools down quickly. This property 
makes water as a excellent cooling agent. 
(b) Water pipes bursts in severe winter because the water inside I the pipes freezes and 
increases its volume. 
(c) Water boils at a lower temperature in the hills, where the atmospheric pressure is lower than 
in the plains. This is why it takes a longer time to cook in hilly regions. 
(d) Ice has low density as compared to water. Water has maximum density at 4°C. That is why 
ice floats on water. 
(e) There are impurities dissolved in sea water which increases the freezing point. That is why 
sea water does not freeze at 0°C. 
Question 7. 
How does anomalous expansion of water help aquatic organisms in cold climates ? 
Answer: 
The anomalous expansion of water helps in survivals of water animals in very cold climates. 
Initially when temperature of water falls, it becomes heavier and sinks down. This process 
continues till 4°C. Then after this expansion takes place. The surface layer of water gets 
freezed. Ice being bad conductor of heat does not allow loss of heat from the water below and 
results in survival of water animals. 
Exercise – II 
Question 1. 
Explain the terms: 
(a) Solution (b) Solute (c) Solvent. 
Answer: 
(a) Solution: “A homogeneous mixture of two or more substances can be varied is 
called a solution”. 
(b) Solute: A substance which dissolves in a other substances to form a solution is 
called solute. Solute is smaller quantity in solution. 
Or 
“Substance which is dissolved in solvent.” is called Solute. Solute is smaller quantity in 
solution. 
(c) Solvent: A solvent is a medium in which a solute dissolves. It is in large quantity in 
solution. 
Solution = Solute + Solvent 
Question 2. 
What is meant by 
(a) Unsaturated (b) Saturated and 
(c) Supersaturated solutions. 
Answer: 
(a) Unsaturated solutions — A solution in which more of the solute can be dissolved 
at a given temperature is called an unsaturated solution. 
(b) Saturated solutions — A solution that cannot dissolve any more of the solute at a 
given temperature is called a saturated solution. 
(c) Supersaturated solutions — A solution that contains more solute than it can hold 
at room temperature is called supersaturated solution. 
Question 3. 
How do the solubility of a solid and a gas affected by – 
(a) Increase in temperature 
(b) Increase in pressure 
Answer: 
(a) Solubility of a solid solute generally increases with an increase in temperature. This 
makes it possible to prepare supersaturated solutions. 
Solubility of a gas decreases with an increase in temperature. 
(b) Pressure has practically no effect on the solubility of a solid (solute) in water. 
In the case of gases, the amount of a gas dissolved in water increases with an increase 
in pressure. 
Page 4


Water 
Points to Remember: 
• Water is the source of life for all living beings. 
• Water occurs in all the three states of matter i.e. ice, liquid water and water 
vapours. 
• Water found in nature (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. 
• Potable water should be free from suspended impurities and harmful germs. 
• Water is a compound, with the molecular formula is H2O. 
• The boiling point of water is 100°C and the freezing point is 0°C. 
• 0°C is also called tripple point, because water can exist in all its three states. 
• The specific heat of water is higher than that of any other liquid. It is used as a 
cooling agent. 
• Water has minimum volume and maximum density at 4°C. This is called 
anomalous behaviour of water. 
• Water is an universal solvent. The gases dissolved in water have biological 
importance. They enable aquatic life to sustain itself. 
• Water may be ‘hard or soft’. Hardness of water can be removed by boiling or by 
chemical treatment. 
• Water pollution is a serious problem. 
• Industrial and agriculture processes, nuclear and thermal plants pollute water. 
Exercise – I 
Question 1. 
Name the four main sources of water. 
Answer: 
(i) Oceans (ii) Seas 
(iii) Rivers (iv) Lakes 
Question 2. 
State the importance of water cycle in nature. 
Answer: 
(i) Water cycle helps in regulating weather on the earth. 
(ii) Water cycle makes water available in various forms on the earth. 
Question 3. 
Why is water very precious for all living beings ? 
Answer: 
Water is one of the most precious substances for the existence of life. Since life on the earth 
began in the oceans, and since no living thing can survive without water, it is rightly called the 
source of life. 
Water forms a large part of the body mass of all living organisms — 90% of human blood is 
water. Water has the ability to dissolve a number of substances. Therefore, it serve as the liquid 
medium in which all reactions within the living body take place. 
Fruits and vegetables contain water in them. Even dry-looking substances like wood, peas, 
beans, grams, etc., contain some amount of water. 
Question 4. 
Name the two gases from which water is formed. What is the chemical composition of these two 
gases in water ? Give the molecular formula of water ? 
Answer: 
Oxygen and hydrogen 
Chemical composition = H2 and O2 proportion 2:1 
Molecular formula = H2O 
Question 5. 
What is the effect on boiling point of water when 
(a) pressure is increased 
(b) impurity is added 
Answer: 
(a) The boiling point of water increases with an increase, in pressure. 
(b) Any impurity present in water lowers its freezing point and raises its boiling point. 
For example, salt is added to ice to lower its melting point. Such a mixture is called a freezing-
mixture. The melting is called a freezing mixture is about -15° C. 
Question 6. 
Give reasons: 
(a) Water is used as a cooling agent 
(b) Water pipes burst in severe winters. 
(c) It is difficult to cook in hills compared to plains. 
(d) Ice floats on water. 
(e) Sea water does not freeze at 0°C. 
Answer: 
(a) Water has high specific heat. Water neither heats up nor cools down quickly. This property 
makes water as a excellent cooling agent. 
(b) Water pipes bursts in severe winter because the water inside I the pipes freezes and 
increases its volume. 
(c) Water boils at a lower temperature in the hills, where the atmospheric pressure is lower than 
in the plains. This is why it takes a longer time to cook in hilly regions. 
(d) Ice has low density as compared to water. Water has maximum density at 4°C. That is why 
ice floats on water. 
(e) There are impurities dissolved in sea water which increases the freezing point. That is why 
sea water does not freeze at 0°C. 
Question 7. 
How does anomalous expansion of water help aquatic organisms in cold climates ? 
Answer: 
The anomalous expansion of water helps in survivals of water animals in very cold climates. 
Initially when temperature of water falls, it becomes heavier and sinks down. This process 
continues till 4°C. Then after this expansion takes place. The surface layer of water gets 
freezed. Ice being bad conductor of heat does not allow loss of heat from the water below and 
results in survival of water animals. 
Exercise – II 
Question 1. 
Explain the terms: 
(a) Solution (b) Solute (c) Solvent. 
Answer: 
(a) Solution: “A homogeneous mixture of two or more substances can be varied is 
called a solution”. 
(b) Solute: A substance which dissolves in a other substances to form a solution is 
called solute. Solute is smaller quantity in solution. 
Or 
“Substance which is dissolved in solvent.” is called Solute. Solute is smaller quantity in 
solution. 
(c) Solvent: A solvent is a medium in which a solute dissolves. It is in large quantity in 
solution. 
Solution = Solute + Solvent 
Question 2. 
What is meant by 
(a) Unsaturated (b) Saturated and 
(c) Supersaturated solutions. 
Answer: 
(a) Unsaturated solutions — A solution in which more of the solute can be dissolved 
at a given temperature is called an unsaturated solution. 
(b) Saturated solutions — A solution that cannot dissolve any more of the solute at a 
given temperature is called a saturated solution. 
(c) Supersaturated solutions — A solution that contains more solute than it can hold 
at room temperature is called supersaturated solution. 
Question 3. 
How do the solubility of a solid and a gas affected by – 
(a) Increase in temperature 
(b) Increase in pressure 
Answer: 
(a) Solubility of a solid solute generally increases with an increase in temperature. This 
makes it possible to prepare supersaturated solutions. 
Solubility of a gas decreases with an increase in temperature. 
(b) Pressure has practically no effect on the solubility of a solid (solute) in water. 
In the case of gases, the amount of a gas dissolved in water increases with an increase 
in pressure. 
Question 4. 
Differentiate between: 
(a) Solution and suspension 
(b) Suspension and colloid 
Answer: 
(a) Solution and suspension 
Solution 
1. It is an example of homogeneous mixture. 
2. Particle size less than 10
-10
m 
3. Transparent 
4. Solute particles can not be filtered. Solution pass easily through filter paper. 
Suspension 
1. It is an example of heterogeneous mixture. 
2. Particle size greater team 10
-7
 m 
3. Opaque 
4. Particles of suspension do not pass through filter paper. 
(b) Suspension and colloids 
Suspension 
1. Heterogeneous 
2. Particle size greater than 10
-7
 m. 
3. Opaque. 
4. Particles are visible. 
5. Particles of suspension settle at the bottom of the container. 
6. Particles of suspension do not pass through filter paper. 
Colloid 
1. Heterogeneous. 
2. Particles size between 10
-10
 to 10
-7
m. 
3. Translucent. 
4. Particles can be seen with the help of a powerful microscope. 
5. Particles of colloids do not settle. 
6. Colloidal particles pass easily through ordinary filter paper but do not pass through 
ultra filters. 
 
Page 5


Water 
Points to Remember: 
• Water is the source of life for all living beings. 
• Water occurs in all the three states of matter i.e. ice, liquid water and water 
vapours. 
• Water found in nature (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. 
• Potable water should be free from suspended impurities and harmful germs. 
• Water is a compound, with the molecular formula is H2O. 
• The boiling point of water is 100°C and the freezing point is 0°C. 
• 0°C is also called tripple point, because water can exist in all its three states. 
• The specific heat of water is higher than that of any other liquid. It is used as a 
cooling agent. 
• Water has minimum volume and maximum density at 4°C. This is called 
anomalous behaviour of water. 
• Water is an universal solvent. The gases dissolved in water have biological 
importance. They enable aquatic life to sustain itself. 
• Water may be ‘hard or soft’. Hardness of water can be removed by boiling or by 
chemical treatment. 
• Water pollution is a serious problem. 
• Industrial and agriculture processes, nuclear and thermal plants pollute water. 
Exercise – I 
Question 1. 
Name the four main sources of water. 
Answer: 
(i) Oceans (ii) Seas 
(iii) Rivers (iv) Lakes 
Question 2. 
State the importance of water cycle in nature. 
Answer: 
(i) Water cycle helps in regulating weather on the earth. 
(ii) Water cycle makes water available in various forms on the earth. 
Question 3. 
Why is water very precious for all living beings ? 
Answer: 
Water is one of the most precious substances for the existence of life. Since life on the earth 
began in the oceans, and since no living thing can survive without water, it is rightly called the 
source of life. 
Water forms a large part of the body mass of all living organisms — 90% of human blood is 
water. Water has the ability to dissolve a number of substances. Therefore, it serve as the liquid 
medium in which all reactions within the living body take place. 
Fruits and vegetables contain water in them. Even dry-looking substances like wood, peas, 
beans, grams, etc., contain some amount of water. 
Question 4. 
Name the two gases from which water is formed. What is the chemical composition of these two 
gases in water ? Give the molecular formula of water ? 
Answer: 
Oxygen and hydrogen 
Chemical composition = H2 and O2 proportion 2:1 
Molecular formula = H2O 
Question 5. 
What is the effect on boiling point of water when 
(a) pressure is increased 
(b) impurity is added 
Answer: 
(a) The boiling point of water increases with an increase, in pressure. 
(b) Any impurity present in water lowers its freezing point and raises its boiling point. 
For example, salt is added to ice to lower its melting point. Such a mixture is called a freezing-
mixture. The melting is called a freezing mixture is about -15° C. 
Question 6. 
Give reasons: 
(a) Water is used as a cooling agent 
(b) Water pipes burst in severe winters. 
(c) It is difficult to cook in hills compared to plains. 
(d) Ice floats on water. 
(e) Sea water does not freeze at 0°C. 
Answer: 
(a) Water has high specific heat. Water neither heats up nor cools down quickly. This property 
makes water as a excellent cooling agent. 
(b) Water pipes bursts in severe winter because the water inside I the pipes freezes and 
increases its volume. 
(c) Water boils at a lower temperature in the hills, where the atmospheric pressure is lower than 
in the plains. This is why it takes a longer time to cook in hilly regions. 
(d) Ice has low density as compared to water. Water has maximum density at 4°C. That is why 
ice floats on water. 
(e) There are impurities dissolved in sea water which increases the freezing point. That is why 
sea water does not freeze at 0°C. 
Question 7. 
How does anomalous expansion of water help aquatic organisms in cold climates ? 
Answer: 
The anomalous expansion of water helps in survivals of water animals in very cold climates. 
Initially when temperature of water falls, it becomes heavier and sinks down. This process 
continues till 4°C. Then after this expansion takes place. The surface layer of water gets 
freezed. Ice being bad conductor of heat does not allow loss of heat from the water below and 
results in survival of water animals. 
Exercise – II 
Question 1. 
Explain the terms: 
(a) Solution (b) Solute (c) Solvent. 
Answer: 
(a) Solution: “A homogeneous mixture of two or more substances can be varied is 
called a solution”. 
(b) Solute: A substance which dissolves in a other substances to form a solution is 
called solute. Solute is smaller quantity in solution. 
Or 
“Substance which is dissolved in solvent.” is called Solute. Solute is smaller quantity in 
solution. 
(c) Solvent: A solvent is a medium in which a solute dissolves. It is in large quantity in 
solution. 
Solution = Solute + Solvent 
Question 2. 
What is meant by 
(a) Unsaturated (b) Saturated and 
(c) Supersaturated solutions. 
Answer: 
(a) Unsaturated solutions — A solution in which more of the solute can be dissolved 
at a given temperature is called an unsaturated solution. 
(b) Saturated solutions — A solution that cannot dissolve any more of the solute at a 
given temperature is called a saturated solution. 
(c) Supersaturated solutions — A solution that contains more solute than it can hold 
at room temperature is called supersaturated solution. 
Question 3. 
How do the solubility of a solid and a gas affected by – 
(a) Increase in temperature 
(b) Increase in pressure 
Answer: 
(a) Solubility of a solid solute generally increases with an increase in temperature. This 
makes it possible to prepare supersaturated solutions. 
Solubility of a gas decreases with an increase in temperature. 
(b) Pressure has practically no effect on the solubility of a solid (solute) in water. 
In the case of gases, the amount of a gas dissolved in water increases with an increase 
in pressure. 
Question 4. 
Differentiate between: 
(a) Solution and suspension 
(b) Suspension and colloid 
Answer: 
(a) Solution and suspension 
Solution 
1. It is an example of homogeneous mixture. 
2. Particle size less than 10
-10
m 
3. Transparent 
4. Solute particles can not be filtered. Solution pass easily through filter paper. 
Suspension 
1. It is an example of heterogeneous mixture. 
2. Particle size greater team 10
-7
 m 
3. Opaque 
4. Particles of suspension do not pass through filter paper. 
(b) Suspension and colloids 
Suspension 
1. Heterogeneous 
2. Particle size greater than 10
-7
 m. 
3. Opaque. 
4. Particles are visible. 
5. Particles of suspension settle at the bottom of the container. 
6. Particles of suspension do not pass through filter paper. 
Colloid 
1. Heterogeneous. 
2. Particles size between 10
-10
 to 10
-7
m. 
3. Translucent. 
4. Particles can be seen with the help of a powerful microscope. 
5. Particles of colloids do not settle. 
6. Colloidal particles pass easily through ordinary filter paper but do not pass through 
ultra filters. 
 
Question 5. 
Define: ‘water of crystallisation’. Give two examples with formulae. 
Answer: 
The fixed amount of water which is in loose chemical combination with a salt in its 
crystal is called water of crystallisation. Examples: 
 
Question 6. 
Give two examples for each of the following: 
(a) Hydrated substances 
(b) Crystalline anhydrous substances 
(c) Drying agents 
(d) Deliquescent substances 
(e) Efflorescent substances 
(f) Colloids 
(g) Solvents other than water. 
Answer: 
(a) Washing soda, Glauber’s salt (Na2SO4.10H2O) 
(b) Common salt (NaCl), potassium nitrate (KNO3), sugar (C12H22O111) etc. 
(c) Concentrated sulphuric acid (H2SO4), phosphorus pentoxide (P2O5), quicklime (CaO) 
(d) Caustic soda (NaOH), crystalline-magnesium chloride (MgCl2), calcium chloride 
(CaCl2), Iron (III) chloride etc. 
(e) Washing soda and glauber’s salt (Na2SO4.10 H2O) 
(f) Milk, blood, smoke, jellies, butter, ink etc. 
(g) Acetone, ethanol, turpentive 
Question 7. 
What do you observe when: 
(a) Blue vitriol is heated ? 
(b) Washing soda is exposed to air ? 
(c) Blue litmus solution is added to water ? 
Answer: 
(a) Blue vitriol is blue in colour as it contains 5 molecules of water of crystallisation 
(CuSO^HjO). When it is heated, it loses water of crystallisation and becomes an 
hydrous CuS04 which is grey-white in colour. 
(b) Washing soda (Na2CO3.10H2O) is a white crystalline substance and on exposure to 
air it gets changed to white powder. 
(c) Pure water is neutral to litmus which means that no change in the colour of blue or 
red litmus solution is observed when 1 treated with water.