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Exercises · 9.20

Q.Complete the following chemical reactions.

(i) PbS(s) + H2O2(aq) ->
(ii) MnO4-(aq) + H2O2(aq) ->
(iii) CaO(s) + H2O(g) ->
(v) AlCl3(g) + H2O(l) ->
(vi) Ca3N2(s) + H2O(l) -> Classify the above into
(a) hydrolysis,
(b) redox and
(c) hydration reactions.
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(i) Lead(II) sulphide is oxidised by hydrogen peroxide to lead(II) sulphate — a redox reaction (S²⁻ oxidised from −2 to +6 in sulphate; H2O2's O reduced from −1 to −2):

PbS(s)+4H2O2(aq)→PbSO4(s)+4H2O(l)PbS(s) + 4H_2O_2(aq) \rightarrow PbSO_4(s) + 4H_2O(l)

(ii) Permanganate oxidises hydrogen peroxide (H2O2 here acts as a reducing agent, being oxidised to O2) — a redox reaction:

2MnO4−(aq)+3H2O2(aq)→2MnO2(s)+3O2(g)+2H2O(l)+2OH−(aq)2MnO_4^-(aq) + 3H_2O_2(aq) \rightarrow 2MnO_2(s) + 3O_2(g) + 2H_2O(l) + 2OH^-(aq)

(iii) Calcium oxide combines with water/steam to give calcium hydroxide, with no bond-breaking of water and no change in oxidation states — a hydration reaction:

CaO(s)+H2O(g)→Ca(OH)2(s)CaO(s) + H_2O(g) \rightarrow Ca(OH)_2(s)

(iv) Aluminium chloride reacts with water, being broken down (hydrolysed) into aluminium hydroxide and hydrochloric acid — a hydrolysis reaction:

AlCl3(g)+3H2O(l)→Al(OH)3(s)+3HCl(aq)AlCl_3(g) + 3H_2O(l) \rightarrow Al(OH)_3(s) + 3HCl(aq) …

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