pBlock ElementsII 2 Question 49
52. Give reasons for the following in one or two sentences.
(i) Hydrogen bromide cannot be prepared by the action of conc. sulphuric acid on sodium bromide.
(ii) When a blue litmus paper is dipped into a solution of hypochlorous acid, it first turns red and then later gets decolourised.
(1979, 2M)
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Solution:
- (i) $\mathrm{HBr}$ is a stronger reducing agent, reduces cencentrated $\mathrm{H}{2} \mathrm{SO}{4}$ to $\mathrm{SO}{2}$. Hence, $\mathrm{HBr}$ cannot be prepared by heating bromide salts with concentrated $\mathrm{H}{2} \mathrm{SO}_{4}$.
(ii) Hypochlorous acid is acidic in nature, therefore it turns blue litmus paper into red. However, $\mathrm{HOCl}$ is also an oxidising acid (bleaching), it bleaches red colour to finally colourless.
