Acids Bases and Salts Exe-3(A) Concise Class-10 ICSE Chemistry Selina Solutions Chapter-3. We Provide Step by Step Answer of Exe-3(A) 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(A) 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(A)
Edition	2025-2026

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

Page-48

Que-1: What do you understand by an alkali? Give two examples of :

(a) Strong alkalis
(b) Weak alkalis

Ans: 
An alkali is a basic hydroxide which when dissolved in water produces hydroxyl ions (OH^–) as the only negatively charged ions.
(a) Strong alkalis: Sodium hydroxide , Potassium hydroxide
(b) Weak alkalis: Calcium hydroxide , Ammonium hydroxide

Que-2: What is the difference between :

(a) An alkali and a base
(b) The chemical nature of an aqueous solution of HCl and an aqueous solution of NH₃

Ans: 
(a) An alkali and a base:
(i) Alkalis are soluble in water whereas bases may be or may not be soluble in water.
(ii) All alkalis are bases but all bases are not alkalis.
(b) The chemical nature of an aqueous solution of HCl and an aqueous solution of NH₃
(i) The aqueoussolution of HCl is acidic in nature. It can turn blue litmus to red.
(ii) The aqueoussolution of NH₃ is basic in nature. It can turn red litmus to blue.

Que-3: Name the ions furnished by

(a) bases in solution
(b) an acid

Ans: 
(a) Hydroxyl ion (OH^–)
(b) H⁺

Que-4: Give one example in each case:

(a) A basic oxide which is soluble in water,
(b) A hydroxide which is highly soluble in water,
(c) A basic oxide which is insoluble in water,
(d) A hydroxide which is insoluble in water,
(e) A weak mineral acid,
(f) A base which is not an alkali,
(g) An oxide which is a base,
(h) A hydrogen containing compound which is not an acid,
(i) A base which does not contain a metal ion.

Ans: 
(a) Barium oxide
(b) Sodium hydroxide
(c) Manganese oxide
(d) Cupper hydroxide
(e) Carbonic acid
(f) Ferric hydroxide
(g) Copper oxide
(h) Ammonia
(i) Ammonium hydroxide

Que-5: You have been provided with three test tubes. One of them contains distilled water and the other two have an acidic solution and a basic solution respectively. If you are given red litmus paper, how will you identify the contents of each test tube?

Ans: 
The test tube containing distilled water does not affect the red litmus paper.
The test tube containing acidic solution does not change the red litmus paper.
But the test tube containing basic solution turns red litmus paper blue.

Que-6: HCl, HNO₃, C₂H₅OH, C₆H₁₂O₆ all contain H atoms but only HCl and HNO₃ show acidic character. Why?

Ans: 
It is because HCl and HNO₃ ionize in aqueous solution whereas ethanol and glucose do not ionize in aqueous solution.

Que-7: 

(a) Dry HCl gas does not change the colour of dry litmus paper. Why?
(b) lsPbO₂ a base or not? Comment.
(c) Do basic solutions also have H⁺_(aq)? Explain why they are basic by taking an example ?

Ans: 
(a) Dry HCl gas does not contain any hydrogen ions in it, so it does not show acidic behaviour. Hence, dry HCl gas does not change the colour of dry litmus paper.
(b) Lead oxide is a metallic oxide which reacts with hydrochloric acid to produce lead chloride and water, but it is excluded from the class of bases, because chlorine is also produced.
PbO₂ + 4HCl → PbCl₂ + Cl₂ + 2H₂O
Thus, lead oxide is not a base.
(c) Yes, basic solutions have H⁺ ions, but the concentration of OH^– ions is more than the H⁺ ions which makes the solution basic in nature.

Que-8: How would you obtain:

(a) a base from another base,
(b) an alkali from a base,
(c) salt from another salt?

Ans:
(a) A base from another base can obtained by double decomposition. The aqueous solution of salts with base (alkali) precipitates the respective metallic hydroxide.
For example,
FeCl₃ + 3NaOH ⟶ 3NaCl + Fe(OH)₃ ↓ [red brown ppt.]
(b) An alkali from a base can be obtained by the action of water on soluble metallic oxides like oxides of sodium, potassium and calcium:
CaO + H₂O ⟶ Ca(OH)₂
(c) A salt from another salt can be obtained by adding an alkali to the solutions of the salts of the heavy metals like copper, iron, zinc, etc.
For example,
FeSO₄ [aq.] + 2NaOH [aq.] ⟶ Na₂SO₄ [aq.] + Fe(OH)₂ ↓ [dirty green]

Que-9: Write balanced equations to satisfy each statement.

(a) Acid + Active metal ⟶ Salt + Hydrogen
(b) Acid + Base ⟶ Salt + Water
(c) Acid + carbonate or bicarbonate ⟶ Salt + water + carbon dioxide
(d) Acid + sulphite or bisulphite ⟶ Salt + water + sulphur dioxide
(e) Acid + sulphide ⟶ Salt + hydrogen sulphide

Ans:
(a) Mg + 2HCl ⟶ MgCl₂ + H₂
(b) HCl + NaOH ⟶ NaCl + H₂O
(c) CaCO₃ + 2HCl ⟶ CaCl₂ + H₂O + CO₂
(d) CaSO₃ + 2HCl ⟶ CaCl₂ + H₂O + SO₂
(e) ZnS + 2HCl ⟶ ZnCl₂ + H₂S

Que-10: The skin has and needs natural oils. Why is it advisable to wear gloves while working with strong alkalis?

Ans: As we know that alkalis react with oil to form soap. As our skin contains oil so when we touch strong alkalis, a reaction takes place and soapy solution is formed. Hence we should wear gloves.

Que-11: Complete the table:

Indicator	Neutral	Acidic	Alkaline
Litmus Phenol-phthalein	Purple Colourless

 

Ans: 

Indicator	Neutral	Acidic	Alkaline
Litmus Phenol-phthalein	Purple Colourless	Blue to red Colourless	Red to blue Pink

Que-12: What do you understand by pH value? Two solutions X and Y have pH values of 4 and 10, respectively. Which one of these two will give a pink colour with phenolphthalein indicator?

Ans: pH represents the strength of acids and alkalis expressed in terms of hydrogen ion concentration. The solution with pH value 10 will give pink colour with phenolphthalein indicator.

Que-13: M is an element in the form of a powder. M burns in oxygen and the product obtained is soluble in water. The solution is tested with litmus. Write down only the word which will correctly complete each of the following sentences.

(i) If M is a metal, then the litmus will turn _____________.
(ii) If M is a non-metal, then the litmus will turn ______________.
(iii) If M is a reactive metal, then _________________ will be evolved when M reacts with dilute sulphuric acid.
(iv) If M is a metal, it will form ______________ oxide, which will form ____________ solution with water.
(v) If M is a non-metal, it will not conduct electricity in the form of __________.

Ans: 
(i) If M is a metal, then the litmus will turn blue.
(ii) If M is a non-metal, then the litmus will turn red.
(iii) If M is a reactive metal, then hydrogen gas will be evolved when M reacts with dilute sulphuric acid.
(iv) If M is a metal, it will form basic oxide, which will form alkaline solution with water.
(v) If M is a non-metal, it will not conduct electricity in the form of graphite.

Que-14: Distinguish between :

(a) a common acid base indicator and a universal indicator.
(b) acidity of bases and basicity of acids,
(c) acid and alkali (other than indicator)

Ans:
(a) Difference between a common acid base indicator and a universal indicator:

Common acid-base indicator	Universal indicator
Common acid-base indicators test whether a solution is acidic, basic or neutral.	Universal indicator gives a spectrum of colours depending upon how acidic or alkaline a solution is.
Common acid-base indicators does not give the exact pH value of the solution.	Universal indicator helps to get a reasonably accurate pH value.

(b) Difference between acidity of bases and basicity of acids:

Acidity of bases	Basicity of acids
The acidity of bases is the number of hydroxyl ions [OH–] which can be produced per molecule of the base in aqueous solution.	The basicity of an acid is defined as the number of hydronium ions [H3O+] that can be produced by the ionisation of one molecule of that acid in aqueous solution.
On the basis of their acidity, bases are classified as Monoacidic base, Diacidic base and Triacidic base.	On the basis of their basicity, acids are classified as Monobasic acids, Dibasic acids and Tribasic acids.

(c) Difference between acid and alkali (other than indicator):

Acid	Alkali
Acids are compounds which contain one or more hydrogen atoms and when dissolved in water, produce hydronium ions [H3O+] as the only positively charged ions.	An alkali is a basic hydroxide which when dissolved in water produces hydroxyl [OH–] ions as the only negatively charged ions.
Acids have a sour taste.	Alkalis have a sharp and bitter taste.
Acids have pH value less than 7.	Alkalis have pH value greater than 7.

Que-15: What should be added to neutral solution in order to :

(a) increase the concentration of hydronium ions,
(b) decrease the concentration of hydronium ions

Ans:
(a) Acid
(b) Alkali

Que-16: How does tooth enamel get damaged? What should be done to prevent it?

Ans: Substances like chocolates and sweets are degraded by bacteria present in our mouth. When the pH falls to 5.5 tooth decay starts. Tooth enamel is the hardest substance in our body and it gets corroded. The saliva produced by salivary glands is slightly alkaline, it helps to increase the pH, to some extent, but toothpaste which contains basic substance is used to neutralize excess acid in the mouth.

Que-17: When you use universal indicator, you see that solutions of different acids produce different colours. Indeed, solution of the same acid with different concentrations will also give different colours. Why?

Ans: A universal indicator is a mixture of dyes which identify a gradual change of various colours over a wide range of pH, depending on the strength of the acid. When we use a universal indicator, we see solutions of different acids produce different colours. Indeed, solutions of the same acid with different concentration give different colours.

The more acidic solutions turn universal indicator bright red. A less acidic solution will only turn it orange-yellow. Colour differences can also be observed in case of vinegar which is less acidic and battery acid which is more acidic.

Que-18: You are supplied with five solutions : A , B , C , D and E with pH values as follows:

A = 1.8, B = 7, C = 8.5, D = 13, and E = 5
Classify these solutions as neutral, slightly or strongly acidic and slightly or strongly alkaline.
Which solution would be most likely to liberate hydrogen with:
(a) magnesium powder
(b) powdered zinc metal.
Give a word equation for each reaction.

Ans:
A = Strongly acidic
B = neutral
C = slightly alkaline
D = Strongly alkaline
E = slightly acidic
(a) Solution A (acidic solution)
Solution A (acidic solution) + magnesium powder ⟶ Hydrogen + Mg salt
(b) Solution A (acidic solution)
Solution A (acidic solution) + powdered zinc metal ⟶ Hydrogen + Zn salt

Que-19: Solution P has a pH of 13, solution Q has a pH of 6 and solution R has a pH of 2. Which solution

(a) will liberate ammonia from ammonium sulphate on heating?
(b) is a strong acid?
(c) contains molecules as well as ions?

Ans:
(a) Solution P
(b) Solution R
(c) Solution Q

Que-20: Select the word/s given which are required to correctly complete the blanks :

[ammonia, ammonium carbonate, carbonate, carbon dioxide, hydrogen, hydronium, hydroxide, precipitate, salt, water]
(i) A solution M turns blue litmus red, so it must contain (1) …………… ions; another solution O turns red litmus blue and hence it must contain (2) …………… ions.
(ii) When solution M and O are mixed together, the products will be (3) …………… and (4) ……………
(iii) If a piece of magnesium was put into solution M, (5) …………… gas would be evolved.

Ans:
(i) A solution M turns blue litmus red, so it must contain (1) hydronium ions ; another solution O turns red litmus blue and hence, must contain, (2) hydroxide ions.
(ii) When solution M and O are mixed together, the prod­uct will be (3) salt and (4) water.
(iii) If a piece of magnesium was put into a solution M, (5) hydrogen gas would be evolved.

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