pBlock ElementsII 1 Question 115
112. Explain the following in not more than two sentences .
(i) Conc. $\mathrm{HNO}_{3}$ turns yellow in sunlight.
(ii) Bleaching powder loses its bleaching properties when it is kept in an open bottle for a long time.
(1980, 2M)
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Solution:
- (i) In the presence of sunlight, concentrated nitric acid decomposes partially as
$$ \text { Conc. } \mathrm{HNO}{3} \stackrel{h \nu}{\longrightarrow} \mathrm{NO}{2}+\mathrm{H}^{+}+\mathrm{O}_{2} $$
It is the $\mathrm{NO}_{2}$ which impart yellow colouration to nitric acid.
(ii) The bleaching action of bleaching powder is due to presence of available chlorine, but in contact of moisture, it releases chlorine decreasing the amount of available chlorine. Hence, bleaching property decreases gradually as bleaching powder is kept in open container for long time.
