ICSE Class 8 Chemistry Chapter 8 Water Selina Solutions

Introduction

Water is one of the most important substances on Earth. It is essential for the survival of all living organisms and plays a vital role in various natural and industrial processes. In the ICSE Class 8 Chemistry syllabus, Chapter 8 – Water introduces students to the physical and chemical properties of water, its importance, purification methods, and water pollution.
This page provides complete ICSE Class 8 Chemistry Chapter 8 Water Selina Solutions, detailed explanations, and important notes to help students prepare effectively for examinations.

Study Support by Rohit Academy

Rohit Academy offers expert-curated ICSE Class 8 Chemistry Study Materials including ICSE Water Selina Solutions, diagrams, and key formulas for better understanding.

You can also visit :

Exercise (I) – (A) Objective Type Questions

Question 1
Choose the correct answer from the multiple choices given below.

Question 1(i)
The purest form of natural water is :
(a) sea water               (b) rain water
(c) river water              (d) spring water
Answer:
(b) Rain water
Explanation:
Rain water is formed by evaporation and condensation during the water cycle. When water evaporates, it leaves impurities behind. So rain water is the purest natural form of water (before it touches the ground).

Question 1(ii)
The ratio of hydrogen and oxygen by mass in a molecule of water is :
(a) 1 : 16                     (b) 2 : 8
(c) 1 : 8                       (d) 8 : 1
Answer:
(c) 1 : 8
Explanation:
Water is H₂O
Atomic mass of Hydrogen = 1
Atomic mass of Oxygen = 16
So,
2 × 1 (Hydrogen) = 2
1 × 16 (Oxygen) = 16
Ratio = 2 : 16 = 1 : 8

Question 1(iii)
Sea water contains a large amount of:
(a) suspended impurities
(b) dissolved common salt
(c) oily substances
(d) none of the above
Answer:
(b) Dissolved common salt
Explanation:
Sea water contains a high amount of dissolved salts, mainly sodium chloride (common salt). That is why sea water tastes salty.

Question 1(iv)
Water returns on earth’s surface from the atmosphere by the process of:
(a) combustion                   (b) respiration
(c) photosynthesis              (d) condensation
Answer:
(d) Condensation
Explanation:
Water vapour cools in the atmosphere and changes into tiny water droplets (condensation). These droplets form clouds and fall as rain, bringing water back to the earth.

Question 1(v)
Spring water is classified as:
(a) surface water
(b) above surface water
(c) underground water (d) none of these
Answer:
(c) Underground water
Explanation:
Spring water comes from water stored beneath the earth’s surface. It naturally flows out from underground sources, so it is classified as underground water.

Question 2
Name the four main sources of water.
Answer:
The four main sources of water are:

1. Ocean and sea water
2. River and lake water
3. Spring and well water
4. Rainwater

Exercise (I) – (B) Short Answer Type Questions

Question 1
What is the importance of water cycle in nature?
Answer:
The water cycle is important because:

• It maintains the balance of water on the earth.
• It provides fresh water through rainfall.
• It helps in climate regulation.
• It supports plant, animal, and human life.
• It purifies water naturally through evaporation.

Question 2
Name the two gases from which water is formed. What is the chemical composition of these two gases in water by mass? Give the molecular formula of water.
Answer:

• Water is formed from Hydrogen gas and Oxygen gas.
• By mass, the ratio of hydrogen to oxygen in water is 1 : 8.
• The molecular formula of water is H₂O.

Question 3
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 as compared to plains.
(d) Ice floats on water.
(e) Sea water does not freeze at 0°C.
(f) Aquatic plants and animals survive in very cold regions.
(g) Water is used in room coolers and hot water bags.

Answer:

(a) Water has a high specific heat capacity, so it absorbs a large amount of heat without a big rise in temperature. Hence, it is used for cooling.

(b) Water expands on freezing. When water inside pipes freezes, it increases in volume and causes the pipes to burst.

(c) At higher altitudes, atmospheric pressure is low, so water boils at a lower temperature. Food takes longer to cook at lower boiling temperatures.

(d) Ice is less dense than water because water expands on freezing. Therefore, ice floats.

(e) Sea water contains dissolved salts, which lower its freezing point. So it freezes below 0°C.

(f) When water freezes, only the surface turns into ice. The lower layers remain liquid, allowing aquatic life to survive.

(g) Water absorbs heat easily (used in coolers) and also retains heat for a long time (used in hot water bags).

Question 4
What is the effect on boiling point of water when:
(a) pressure is increased?
(b) impurity is added?

Answer:

(a) When pressure is increased, boiling point of water is increased.
(b) When impurity is added, the boiling point of water increases.

Exercise (I) – (C) Long Answer Type Questions

Question 1
Why is water very precious for all living beings? List four points.

Answer:

1. Water is essential for all life processes such as digestion, respiration, and excretion.
2. It helps plants prepare food through photosynthesis.
3. It regulates body temperature in living organisms.
4. It is necessary for agriculture, hygiene, and daily activities.

Question 2

How does anomalous expansion of water help the aquatic organisms in cold climates?

Answer:

Water shows anomalous expansion, that is, it expands on cooling below 4°C and becomes less dense on freezing. In cold regions, the surface water of lakes and ponds freezes first and forms a layer of ice. Since ice is lighter than water, it floats and forms an insulating layer on the surface. This prevents the water below from freezing completely and maintains it at about 4°C. As a result, aquatic plants and animals are able to survive in the liquid water beneath the ice during severe winters.

Exercise (II) – (A) Objective Type Questions

Question 1
Choose the correct answer from the multiple choices given below.

Question 1(i)
The gases dissolved in natural water are:
(a) oxygen and carbon dioxide
(b) hydrogen and oxygen
(c) sulphur dioxide and hydrogen
(d) chlorine and ammonia
Answer:
(a) oxygen and carbon dioxide
Explanation:
Natural water (river, lake, pond water) contains dissolved oxygen and carbon dioxide from the air. Oxygen helps aquatic animals to breathe, and carbon dioxide is used by aquatic plants for photosynthesis.

Question 1(ii)
Colloids have the particle size ranging between:
(a) 10^–7 to 10^–10 m       (b) 10^–10 to 10^–12 m
(c) 10^–7 to 10^–5 m        (d) 10^–12 to 10^–15 m
Answer:
(c) 10^–7 to 10^–5 m
Explanation:
Colloidal particles are bigger than particles in a true solution but smaller than particles in a suspension. Their size ranges between 10^–7 m and 10^–5 m.

Question 1(iii)
Which of the following salts is hydrated?
(a) Common salt        (b) Potassium nitrate
(c) Blue vitriol            (d) Ammonium chloride
Answer:
(c) Blue vitriol
Explanation:
Copper(II) sulphate pentahydrate (Blue vitriol) is a hydrated salt because it contains water of crystallization (CuSO₄·5H₂O). The other salts listed do not contain water molecules in their crystals.

Question 1(iv)
Which of the following substances is hygroscopic in nature ?
(a) silica gel                  (b) caustic soda
(c) iron (III) chloride      (d) calcium carbonate
Answer:
(a) Silica gel
Explanation:
Certain substances absorb moisture (water vapour) from the atmosphere without dissolving in it. Such substances are called hygroscopic substances. Silica gel absorbs moisture from the air and is therefore used as a drying agent.

Question 1(v)
The products formed when water is subjected to electrolysis are:
(a) hydrogen and oxygen
(b) hydrogen and sulphur dioxide
(c) only hydrogen
(d) only oxygen
Answer:
(a) hydrogen and oxygen
Explanation:
When water is passed with electric current (electrolysis), it breaks down into hydrogen gas and oxygen gas. Hydrogen is produced at the cathode and oxygen at the anode.

Question 2
Classify the following into solutions, colloids and suspensions :
Sugar and water, chalk and water, milk, sand and water, salt and water, soap solution.
Answer:

(a) Solutions : Sugar and water, salt and water.
(b) Colloids : milk, soap solution.
(c) Suspensions : chalk and water, sand and water.

Question 3
Name the gas produced when:
(a) steam is passed over hot coke.
(b) chlorine is dissolved in water and exposed to sunlight.
(c) a piece of calcium is added to water.
(d) when fossil fuel is burnt.

Answer:

(a) Water gas [CO + H₂]
(b) Oxygen gas (O₂)
(c) Hydrogen gas (H₂)
(d) Carbon dioxide gas (CO₂)

Exercise (II) – (B) Short Answer Type Questions

Question 1
Define the following terms :
(a) Solution
(b) Solute
(c) Solvent

Answer:

(a) A solution is a homogeneous mixture of two or more substances.

(b) The solute is the substance that dissolves in a solvent.

(c) The solvent is the substance that dissolves the solute.

Question 2
What is meant by :
(a) Unsaturated
(b) Saturated and
(c) Supersaturated solutions ?

Answer:

(a) A solution that can dissolve more solute at a given temperature is called an unsaturated solution.

(b) A solution that cannot dissolve any more solute at a given temperature is called a saturated solution.

(c) A solution that contains more solute than it can normally dissolve at that temperature is called a supersaturated solution.

Question 3
How do the solubility of a solid and a gas get affected by:
(a) Increase in temperature ?
(b) Increase in pressure ?
Answer:

(a) The solubility of most solids increases when the temperature rises.
However, the solubility of gases decreases as the temperature increases.

(b) Pressure has almost no effect on the solubility of solids in water.
But for gases, solubility increases with an increase in pressure and decreases when the pressure is reduced.

Question 4
Define ‘water of crystallisation’. Give two examples with formulae.
Answer:
The fixed number of water molecules chemically combined with a salt in its crystal form is called water of crystallisation.

Examples:

1. Copper(II) sulphate pentahydrate (CuSO₄.5H₂O)
2. Sodium carbonate decahydrate (Na₂CO₃.10H₂O)

Question 5
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) Blue vitriol (CuSO₄.5H₂O), Washing soda (Na₂CO₃.10H₂O)

(b) Common salt (NaCl), Potassium nitrate (KNO₃)

(c) Quicklime (CaO), Anhydrous calcium chloride (CaCl₂)

(d) Caustic soda (NaOH), Magnesium chloride (MgCl₂)

(e) Washing soda (Na₂CO₃.10H₂O), Glauber’s salt (Na₂SO₄.10H₂O)

(f) Milk, blood

(g) Alcohol, Carbon tetrachloride

Question 6
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) When blue vitriol is heated, Copper(II) sulphate pentahydrate loses water of crystallisation and turns from blue to white.

(b) When washing soda is exposed to air, Washing soda loses water of crystallisation and becomes a white powder.

(c) There is no change in colour because pure water is neutral.

Question 7
What is metal activity series?

Answer:

The reactions of different metals with water under various conditions show their relative reactivity. Based on these reactions, metals can be arranged in order of their reactivity, which is known as the metal activity series.
Example (most reactive to least reactive):
K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au

Question 8
Give balanced chemical equations for the reaction of water with:
(a) Sodium
(b) Iron
(c) Carbon dioxide
(d) Sodium oxide

Answer:

(a) 2Na + 2H₂O ⟶ 2NaOH + H₂ (g)
(b) 3Fe + 4H₂O ⇌ Fe₃O₄ + 4H₂ (g)
(c) CO₂ + H₂O ⟶ H₂CO₃
(d) Na₂O + H₂O ⟶ 2NaOH

Exercise (II) – (C) Long Answer Type Questions

Question 1
Differentiate between:
(a)  Solution and suspension
(b)  Suspension and colloid

Answer:

(a) Difference between Solution and Suspension:

(b) Difference between Suspension and Colloid:

Question 2
Give reason :
(a) Water is called a universal solvent.
(b) Silica gel pouches are kept in unused water bottles.
(c) Table salt becomes moist during rainy season.
(d) On opening a bottle of a cold drink, a fizz sound is heard.

Answer:

(a) Water is called a universal solvent because water dissolves a large number of substances (solids, liquids and gases), it is called the universal solvent.

(b) Silica gel is a drying agent that absorbs moisture from the air, keeping the bottles dry and preventing damage.

(c) Sodium chloride absorbs moisture from the air (due to impurities like magnesium chloride), so it becomes moist in humid weather.

(d) Cold drinks contain dissolved carbon dioxide under high pressure. When the bottle is opened, pressure decreases and the gas escapes quickly, producing a fizz sound.

Exercise (III) – (A) Objective Type Questions

Question 1
Choose the correct answer from the multiple choices given below.

Question 1(i)
The salt which gives water vapour on heating is called :
(a) Hydrated                (b) Hygroscopic
(c) Deliquescent          (d) Anhydrous
Answer:
(a) Hydrated
Explanation:
A hydrated salt contains water of crystallisation (fixed water molecules in its crystals). When heated, it loses this water in the form of water vapour. For example, copper sulphate crystals lose water on heating and turn white.

Question 1(ii)
Which of the following salts cause permanent hardness of water ?
(a) Calcium sulphate       (b) Calcium bicarbonate
(c) Sodium chloride         (d) Magnesium nitrate
Answer:
(a) Calcium sulphate 
Explanation:
Permanent hardness is caused by the presence of sulphates and chlorides of calcium and magnesium.

Question 1(iii)
The substance which can remove permanent hardness of water is :
(a) sodium bicarbonate      (b) sodium carbonate
(c) sodium hydroxide         (d) sodium chloride
Answer:
(b) Sodium carbonate
Explanation:
Sodium carbonate (washing soda) reacts with calcium and magnesium salts to form insoluble carbonates, which settle down and can be removed by filtration. Hence, it removes permanent hardness.

Question 1(iv)
Temporary hardness of water can be removed by:
(a) filtering                          (b) boiling these
(c) loading                          (d) none of the above
Answer:
(b) Boiling these
Explanation:
Temporary hardness is caused by bicarbonates of calcium and magnesium. On boiling, these bicarbonates decompose into insoluble carbonates, carbon dioxide, and water. The insoluble carbonates settle down, thus removing hardness.

Question 2
The following questions are Assertion-Reason based questions. Choose the answer based on the codes given below.

Question 2(i)
Assertion (A): Water is a universal solvent.
Reason (R): We use water daily for drinking, washing, bathing, etc.
(i) Both A and R are true and R is the correct explanation of A.
(ii) Both A and R are true but R is not the correct explanation of A.
(iii) A is true but R is false.
(iv) A is false but R is true.
Answer:
(i) Both A and R are true but R is not the correct explanation of A.
Explanation:
Water is called a universal solvent because it dissolves a large number of substances due to its chemical nature (polarity). The reason given only tells us that we use water daily, which is true, but it does not explain why water is called a universal solvent.

Question 2(ii)
Assertion (A): Water exists in all the three states of matter.
Reason (R): On cooling, liquid water changes into ice, the solid state. On heating, it changes into vapour, the gaseous state.
(i) Both A and R are true and R is the correct explanation of A.
(ii) Both A and R are true but R is not the correct explanation of A.
(iii) A is true but R is false.
(iv) A is false but R is true.
Answer:
(i) Both A and R are true and R is the correct explanation of A.
Explanation:
Water exists in three states — solid (ice), liquid (water), and gas (water vapour). The reason correctly explains that on cooling water becomes ice and on heating it becomes vapour. So, R correctly explains A.

Question 2(iii)
Assertion (A): Miscible liquids dissolve into each other.
Reason (R): Petrol and water are miscible liquids.
(i) Both A and R are true and R is the correct explanation of A.
(ii) Both A and R are true but R is not the correct explanation of A.
(iii) A is true but R is false.
(iv) A is false but R is true.
Answer:
(iii)  A is true but R is false.
Explanation:
Miscible liquids are those that mix completely with each other (like alcohol and water). Petrol and water do not mix; they form separate layers. Therefore, the assertion is true, but the reason is false.

Question 2(iv)
Assertion (A): A solution is a heterogeneous mixture of two or more substances with variable composition.

Reason (R): The component of a solution that dissolves is called as solute, while the other component in which the solute dissolves is called a solvent.
(i) Both A and R are true and R is the correct explanation of A.
(ii) Both A and R are true but R is not the correct explanation of A.
(iii) A is true but R is false.
(iv) A is false but R is true.
Answer:
(iv)  A is false but R is true.
Explanation:
A solution is a homogeneous mixture, not a heterogeneous mixture. So the assertion is false. The reason correctly defines solute and solvent, so it is true.

Question 2(v)
Assertion (A): Pure water is tasteless but the water which we drink has taste.
Reason (R): Drinking water contains dissolved minerals and gases.
(i) Both A and R are true and R is the correct explanation of A.
(ii) Both A and R are true but R is not the correct explanation of A.
(iii) A is true but R is false.
(iv) A is false but R is true.
Answer:
(i) Both A and R are true and R is the correct explanation of A.
Explanation:
Pure water has no taste. Drinking water contains dissolved minerals and gases, which give it taste. Therefore, the reason correctly explains the assertion.

Question 2(vi)
Assertion (A): Hard water does not form lather with soap easily.
Reason (R): Temporary hardness can be removed by boiling.
(i) Both A and R are true and R is the correct explanation of A.
(ii) Both A and R are true but R is not the correct explanation of A.
(iii) A is true but R is false.
(iv) A is false but R is true.
Answer:
(ii) Both A and R are true but R is not the correct explanation of A.
Explanation:
Hard water does not form lather easily because it contains calcium and magnesium salts that react with soap. Temporary hardness can be removed by boiling, which is true, but this does not explain why hard water does not form lather easily.

Question 2
Fill in the blanks:

(a) Water has ………………… density and …………….. volume at 4°C.

(b) Freezing mixture contains ……………… and ……………. .

(c) The solubility of a gas in water …………….. with rise in temperature and ………………….. with rise in pressure.

(d) ………………. is the purest form of natural water.

(e) Use of excessive ……………… by farmers causes water pollution.

(f) Boiling removes the ………………. hardness of water.

(g) Water turns the colour of anhydrous copper sulphate ………………. .

(h) The sticky substance formed when soap is added to hard water is …………………. .

Answer:

(a) Water has maximum density and minimum volume at 4°C.

(b) Freezing mixture contains ice and salt.

(c) The solubility of a gas in water decreases with rise in temperature and increases with rise in pressure.

(d) Rainwater is the purest form of natural water.

(e) Use of excessive fertilisers by farmers causes water pollution.

(f) Boiling removes the temporary hardness of water.

(g) Water turns the colour of anhydrous copper sulphate blue.

(h) The sticky substance formed when soap is added to hard water is scum.

Question 3
Write true or false for the following statements and correct the false ones.

(a) Hard water forms lather easily with soap.

(b) Permanent hardness is due to bicarbonate salts of calcium and magnesium.

(c) Silica gel is a drying agent.

(d) The reaction of steam with magnesium produces hydrogen gas and magnesium hydroxide.

(e) An example of a colloid is ink.

Answer:

(a) False
Correct Statement : Hard water does not form lather easily with soap.

(b) False
Correct Statement : Temporary hardness is due to bicarbonate salts of calcium and magnesium.

(c) True

(d) True

(e) True

Question 4
Match the statements in column A with that in column B.

Answer:

Question 5
Give one word/words for the following statements:

(a) Water fit for human consumption.

(b) The harmful substances dissolved in water.

(c) The change of states of water from one form to another.

(d) The gaseous form of water found in air.

(e) A mixture of common salt and ice.

(f) A substance which does not contain water in its chemical structure.

(g) A property due to which a substance absorbs water without dissolving.

(h) Water molecules in loose chemical combination with other substances.

Answer:

(a) Potable water

(b) Impurities

(c) Water cycle

(d) Water vapours

(e) Freezing mixture

(f) Anhydrous substance

(g) Hygroscopy

(h) Water of crystallisation

Exercise (III) – (B) Short Answer Type Questions

Question 1
Define:
(a) Soft water
(b) Hard water

Answer:

(a) Water which forms a lather with soap easily is called soft water.
(b) Water which does not forms a lather with soap easily rather forms a white sticky scum or precipitate is called hard water.

Question 2
Name three water borne diseases.
Answer:

Three water-borne diseases are:

1. Cholera
2. Typhoid
3. Dysentery

Question 3
Give reasons:
(a) Alcohol is mixed with water and is used in car radiators.
(b) Carbonated drinks are bottled under high pressure.

Answer:

(a) Alcohol is mixed with water and used in car radiators to prevent it from freezing in cold weather, because the presence of alcohol lowers the freezing point of water.

(b) The solubility of a gas in water increases with increase in pressure. Therefore, carbonated drinks are bottled under high pressure so that a large amount of carbon dioxide gas remains dissolved in them.

Exercise (III) – (C) Long Answer Type Questions

Question 1
(a) Name the compounds responsible for:
(i) temporary hardness of water
(ii) permanent hardness of water.

(b) Suggest one method along with the reactions for the removal of:
(i) temporary hardness of water
(ii) permanent hardness of water

Answer:

(a) Compounds responsible for:

(i) Temporary hardness of water:
Temporary hardness is caused by calcium bicarbonate [Ca(HCO₃)₂] and magnesium bicarbonate [Mg(HCO₃)₂].

(ii) Permanent hardness of water:
Permanent hardness is caused by calcium sulphate (CaSO₄), magnesium sulphate (MgSO₄), calcium chloride (CaCl₂) and magnesium chloride (MgCl₂).

(b) Methods of removal with reactions:

(i) Removal of temporary hardness — By Boiling:

On boiling, bicarbonates decompose into insoluble carbonates which settle down.

Reactions:

Ca(HCO₃)₂ \(\xrightarrow{boiled}\) CaCO₃ ↓ + H₂O + CO₂

Mg(HCO₃)₂  \(\xrightarrow{boiled}\) Mg(OH)₂ ↓ + 2CO₂
(White precipitate forms and can be removed.)

(ii) Removal of permanent hardness — By Adding Sodium Carbonate (Washing Soda):

Sodium carbonate reacts with calcium and magnesium salts to form insoluble carbonates.

Reactions:
CaSO₄ + Na₂CO₃ → CaCO₃ ↓ + Na₂SO₄
MgCl₂ + Na₂CO₃ → MgCO₃ ↓ + 2NaCl

Question 2
What are the main causes of water pollution? State three ways to control water pollution.

Answer:

Main Causes of Water Pollution:

1. Discharge of sewage into rivers and lakes
2. Industrial waste and chemicals
3. Excessive use of fertilizers and pesticides in agriculture
4. Oil spills and plastic waste

Three Ways to Control Water Pollution:

1. Treat sewage and industrial waste before releasing into water bodies.
2. Reduce use of chemical fertilizers and pesticides.
3. Proper disposal and recycling of plastic and other wastes.

Download ICSE Class 8 Chemistry Chapter 8 Water Selina Solutions PDF

Students looking for complete ICSE Class 8 Chemistry Chapter 8 Water Selina Solutions PDF can use these notes for revision, homework, and exam preparation. Practice all exercise questions regularly to score better marks in ICSE examinations.

Conclusion

Chapter 8 – Water is an important topic in ICSE Class 8 Chemistry. Students should understand the physical and chemical properties of water, methods of purification, potable water, and the causes and effects of water pollution. Regular practice of Selina textbook questions and revision of key concepts will help students score excellent marks in examinations.

ICSE Class 8 Chemistry Selina Solutions

The Selina Concise Chemistry Class 8 book includes the following chapters:

Official Website:

Students can visit the official CISCE website for more details and updates.

• Council for the Indian School Certificate Examinations (CISCE)