Acids Bases and Salts Exe-3(C) Concise Class-10 ICSE Chemistry Selina Solutions Chapter-3. We Provide Step by Step Answer of Exe-3(C) Questions of Exercise-3 for ICSE Class-10. The given Solutions is according to the Latest editions. Visit official Website CISCE for detail information about ICSE Board Class-10.

Acids Bases and Salts Exe-3(C) Concise Class-10 ICSE Chemistry Selina Solutions Chapter-3

Board	ICSE
Book / Publication	Concise / Selina
Subject	Chemistry
Class	10th
Writer	Dr SP Singh
Chapter-3	Acids Bases and Salts
Topics	Exe-3(C)
Edition	2025-2026

Exe-3(C) Questions on Acids Bases and Salts

Page-61

Que-1: What do you understand by water of crystallisation? Give four substances which contain water of crystallisation and write their common names.

Ans: It is the amount of water molecules which enter into loose chemical combination with one molecule of the substance on crystallization from its aqueous solution.

Common name	Chemical name	Formula
Washing soda	Sodium carbonate dehydrate	Na2CO3.10H2O
Epsom salt	Magnesium sulphate heptahydrate	MgSO4. 7H2O
Potash alum	Hydrated potassium aluminium sulphate	K2SO4.Al(SO4)3.24H2O
Gypsum	Hydrated calcium sulphate	CaSO4.2H2O

Que-2:

(a) Define efflorescence. Give examples.
(b) Define deliquescence. Give examples.

Ans:
(a) Crystalline hydrated salts which on exposure to the atmosphere lose their water of crystallisation partly or completely and change into a powder. This phenomenon is called efflorescent and the salts are called efflorescent.
Examples: CuSO₄.5H₂O, MgSO₄.7H₂O, Na₂CO₃.10H₂O
(b) Water-soluble salts which on exposure to the atmosphere absorb moisture from the atmosphere and dissolve in the same and change into a solution. The phenomenon is called deliquescence and the salts are called deliquescent.
Examples: CaCl₂, MgCl₂, ZnCl₂

Que-3: Answer the questions below relating your answers only to salts in the following list: Sodium chloride, anhydrous calcium chloride, copper sulphate-5-water?

(a) What name is given to the water in the compound copper sulphate-5-water?
(b) If copper sulphate-5-water is heated, anhydrous copper sulphate is formed. What is its colour?
(c) By what means, other than healing, could you dehydrate copper sulphate-5-water and obtain anhydrous copper sulphate?
(d) Which one of the salts in the given list is deliquescent?

Ans:
(a) Water of crystallization
(b) White
(c) By heating with any dehydrating agent
(d) Anhydrous calcium chloride

Que-4: State your observation when the following are exposed to the atmosphere.

(a) Washing soda crystals
(b) Iron (III) chloride salts

Ans:
(a) When washing soda (Na₂CO₃.10H₂O) is exposed to air, it loses 9 molecules of water to form a monohydrate.
(b) It absorbs moisture from the atmosphere and becomes moist and ultimately dissolves in the absorbed water, forming a saturated solution.

Que-5: Give reason for the following:

(a) Sodium hydrogen sulphate is not an acid but it dissolves in water to give hydrogen ions, according to the equation
NaHSO₄ ⇆ H⁺ + Na⁺ + SO₄^2-
(b) Anhydrous calcium chloride is used in a desiccator.

Ans: (a) Sodium hydrogen sulphate [NaHSO₄] is an acid salt and is formed by the partial replacement of the replaceable hydrogen ion in a dibasic acid [H₂SO₄]. The [H] atom in NaHSO₄ makes it behave like an acid.
So, on dissolving in water, it gives hydrogen ions.
(b) Desiccating agents are used to absorb moisture. Anhydrous calcium chloride (CaCl₂) has the capacity of absorbing moisture as it is hygroscopic in nature. So, it is used in a desiccator.

Que-6: Explain clearly how conc. H₂SO₄ is used as a dehydrating as well as a drying agent.

Ans: Conc. sulphuric acid is hygroscopic in nature and can remove moisture from other substances; therefore, it is used as a drying agent.
It is also used as a dehydrating agent because it has a strong affinity for water and thus absorbs water quickly from compounds.

Que-7: Distinguish between drying and dehydrating agent.

Ans:

Drying agents	Dehydrating agents
remove moisture from other substances.	remove chemically combined elements of water in the ratio of 2:1 (hydrogen : oxygen) from a compound.
They are used to dry gases like chlorine, sulphur dioxide and hydrogen chloride. are also used in dessicators to keep substances dry.	prepare substances such as carbon monoxide and sugar charcoal.
represent a physical change.	represent a chemical change.

Que-8: State whether a sample of each of the following would increase or decrease in mass if exposed to air.

(a) Solid NaOH
(b) Solid CaCl₂
(c) Solid Na₂CO₃.10H₂O
(d) Conc. sulphuric acid
(e) Iron (III) chloride

Ans:
(a) Increase
(b) Increase
(c) Decrease
(d) Increase
(e) Increase

Que-9: 

(a) Why does common salt get wet during the rainy season?
(b) How can this impurity be removed?
(c) Name a substance which changes the blue colour of copper sulphate crystals to white.
(d) Name two crystalline substances which do not contain water of crystallisation.

Ans:
(a) Table salt turns moist and ultimately forms a solution on exposure to air especially during the rainy season. Although pure sodium chloride is not deliquescent, the commercial version of the salt contains impurities (such as magnesium chloride) which are deliquescent substances.
(b) The impurity can be removed by passing a current of dry hydrogen chloride gas through a saturated solution of the affected salt. Pure sodium chloride is produced as a precipitate which can be recovered by filtering and washing first with a little water and finally with alcohol.
(c) Conc. sulphuric acid
(d) Common salt and sugar

Que-10: Name the salt which on hydrolysis forms

(a) Acidic
(b) Basic acid
(c) Neutral solution. Give a balanced equation for each reaction.

Ans:
(a) Iron chloride(FeCl₃)
FeCl₃ + 3H₂O → 3HCl + Fe(OH)₃
(b) Ammonium acetate (CH₃COONH₄)
CH₃COONH₄ +H₂O → CH₃COOH + NH₄OH
(c) Sodium chloride
NaCl_(s) + H₂O → Na⁺_(aq)  OH^–_(aq) + H₂O

Que-11: State the change noticed when blue litmus and red litmus are introduced in the following solutions:

(a) Na₂CO₃ solution
(b) NaCl solution
(c) NH₄NO₃
(d) MgCl₂ Solution

Ans:
(a) Na₂CO₃ solution: This solution is alkaline in nature; hence, red litmus changes to blue.
(b) NaCl solution: There is no change in the colour of the litmus paper because this solution is neutral.
(c) NH₄NO₃: This solution is alkaline in nature; hence, red litmus changes to blue.
(d) MgCl₂: It is slightly acidic and neutral; hence, there is no change in the litmus paper.

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