Selina Concise Chemistry Class 10 ICSE Solutions Sulphuric Acid

Selina Concise Chemistry Class 10 ICSE Solutions Sulphuric Acid

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Selina ICSE Solutions for Class 10 Chemistry Chapter 11 Sulphuric Acid

Exercise 1

Solution 1.

(a) Sulphuric acid is called King of Chemicals because there is no other manufactured compound which is used by such a large number of key industries.
(b) Sulphuric acid is referred to as Oil of vitriol as it was obtained as an oily viscous liquid by heating crystals of green vitriol.

Solution 2.

(a) Two balanced equations to obtain SO₂ is:
(i) 4FeS₂ + 11O₂ → 2Fe₂O₃ +8SO₂
(ii) S +O₂ → SO₂

(b) The conditions for the oxidation of SO₂ are:
(i) The temperature should be as low as possible. The yield has been found to be maximum at about 410⁰C-450^oC
(ii) High pressure (2 atm) is favoured because the product formed has less volume than reactant.
(iii) Excess of oxygen increases the production of sulphur trioxide.
(iv) Vanadium pentoxide or platinised asbestos is used as catalyst.

(c) Sulphuric acid is not obtained directly by reacting SO₃ with water because the reaction is highly exothermic which produce the fine misty droplets of sulphuric acid that is not directly absorbed by water.

(d) The chemical used to dissolve SO₃ is concentrated sulphuric acid. The product formed is oleum.

(e) Main reactions of this process are:

Solution 3.

Water is not added to concentrated acid since it is an exothermic reaction. If water is added to the acid, there is a sudden increase in temperature and the acid being in bulk tends to spurt out with serious consequences.

Solution 4.

Impurity of ARSENIC poisons the catalyst [i.e. deactivates the catalyst]. So, it must be removed before passing the mixture of SO₂ air through the catalytic chamber.

Solution 5.

Balanced reactions are:

(a) Acidic nature:

(i) Dilute H₂SO₄ reacts with basic oxides to form sulphate and water.
2 NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O

(ii) CuO + H₂SO₄ → CuSO₄ + H₂O

(iii) It reacts with carbonate to produce CO₂.
Na₂CO₃ + H₂SO₄ → Na₂SO₄ + H₂O + CO₂ ↑

(b) Oxidising agent:

H₂SO₄ → H₂O +SO₂ + [O]
Nascent oxygen oxidizes non-metals, metals and inorganic compounds.
For example,
Carbon to carbon dioxide
C+H₂SO₄ → CO₂ +H₂O +2SO₂

Sulphur to sulphur dioxide
S +H₂SO₄ → 3SO₂ +2H₂O

(c) Hygroscopic nature:

It has great affinity for water. It readily absorbs moisture from atmospheric air.

(d) Non-volatile nature:

It has a high boiling point (356^oC) so it is considered to be non-volatile. Therefore, it is used for preparing volatile acids like hydrochloric acid, nitric acid from their salts by double decomposition reaction.

NaCl + H₂SO₄ → NaHSO₄ + HCl

KCl + H₂SO₄ → KHSO₄ + HCl

Solution 6.

(a) Bring a glass rod dipped in Ammonia solution near the mouth of each test tubes containing dil. Hel and dil. H₂SO₄each.

(b)

1. Dilute sulphuric acid treated with zinc gives Hydrogen gas which bums with pop sound.
   Concentrated H₂SO₄ gives SO₂ gas with zinc and the gas turns Acidified potassium dichromate paper green.
2. Barium chloride solution gives white ppt. with dilute H₂SO₄, This white ppt. is insoluble in all acids.
   Concentrated H₂SO₄ and NaCl mixture when heated gives dense white fumes if glass rod dipped in Ammonia solution is brought near it.

Solution 7.

Solution 8.

(a) Concentrated sulphuric acid is hygroscopic substance that absorbs moisture when exposed to air. Hence, it is stored in air tight bottles.

(b) Sulphuric acid is not a drying agent for H₂S because it reacts with H₂S to form sulphur.
H₂SO₄ + H₂S → 2H₂O + SO₂ + S

(c) Concentrated sulphuric acid has high boiling point (356^oC). So, it is considered to be non-volatile. Hence, it is used for preparing volatile acids like Hydrochloric acid and Nitric acids from their salts by double decomposition.
NaCl + H₂SO₄ → NaHSO₄ + HCl
NaNO₃ + H₂SO₄ → NaHSO₄ + HNO₃

Solution 9.

(a) Due to its reducing property. i.e, it is a non-volatile acid.

NaCl + H₂SO₄ → NaHSO₄ + HCl

(c) Magnesium is present above hydrogen in the reactivity series so sulphuric acid is able to liberate hydrogen gas by reacting with magnesium strip.

Mg + H₂SO₄ → MgSO₄ + H₂

(d) Due to its oxidizing character

Cu +H₂SO₄ → CuSO₄ +2H₂O +SO₂

(e) Due to its oxidizing property Hydrogen sulphide gas is passed through concentrated sulphuric acid to liberate sulphur dioxide and sulphur is formed.

H₂S + H₂SO₄ → S + 2H₂O + SO₂

Solution 10.

The name of the salt of
(a) Hydrogen sulphites and Sulphites.
(b) Sulphate and bisulphate.

Solution 11.

(a) Two types of salts are formed when sulphuric acid reacts with NaOH because sulphuric acid is dibasic.

NaOH + H₂SO₄ → NaHSO₄ + H₂O

2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O

(b) When hydrogen bromide reacts with sulphuric acid the bromine gas is obtained which produce red brown vapours.

2KBr + 3H₂SO₄ → 2KHSO₄ + SO₂ + Br₂ ↑ + 2H₂O

(c) A piece of wood becomes black when concentrated sulphuric acid is poured on it because it gives a mass of carbon.

(d) When sulphuric acid is added to sodium carbonate it liberates carbon dioxide which produces brisk effervescence.

Na₂CO₃ + H₂SO₄ → Na₂SO₄ + H₂O + CO₂ ↑

Solution 12.

Solution 1 (2004).

Hydrogen sulphide (H₂S) can be oxidized to sulphur.

Solution 1 (2006).

(a) The process used for the large-scale manufacture of sulphuric acid is Contact process.

(b) Sulphuric acid has great affinity for water. It readily removes element of water from other compound. Thus it acts as a dehydrating agent.

(c) Concentrated acid is non-volatile thus it is used for the preparation of volatile acids:
NaCl + H₂SO₄ → NaHSO₄ + HCl
Concentrated acid act as an oxidizing agent:
C + 2H₂SO₄ → CO₂ + 2H₂O + 2SO₂

Solution 1 (2007).

(i) B
(ii) D
(iii) C
(iv) A
(v) A

Solution 1 (2008).

(a) Concentrated sulphuric acid is non-volatile; hence it is used for the preparation of higher volatile acids.
(b) Due to its dehydrating nature sugar turns black in the presence of concentrated sulphuric acid.

Solution 2 (2004).

When sodium sulphide is added to solution of HCl, Hydrogen sulphide gas is produced. It has rotten egg like smell.

Solution 2 (2007).

(a) The acid formed when sulphur dioxide dissolves in water is sulphurous acid.
(b) Carbondioxide gas is released when sodium carbonate is added to solution of sulphur dioxide.

Solution 3 (2004).

(a) The catalyst which helps in the conversion of sulphur dioxide to sulphur trioxide in step C is Vanadium pentoxide.
(b) The two steps for the conversion of sulphur trioxide to sulphuric acid is:
(i) SO₃ + H₂SO₄ → H₂S₂O₇
(ii) H₂S₂O₇ + H₂O → 2H₂SO₄
(b) The substance that will liberate sulphur dioxide in step E is dilute H₂SO_4.
(c) The equation for the reaction by which sulphur dioxide is converted to sodium sulphite in step F is:
SO₂ + 2NaOH → Na₂SO₃ + H₂O
Or Na₂O + SO₂ → Na₂SO₃

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