pBlock ElementsII 2 Question 11
11. Among the following oxoacids, the correct decreasing order of acidic strength is
(2014 Main)
(a) $\mathrm{HOCl}>\mathrm{HClO}{2}>\mathrm{HClO}{3}>\mathrm{HClO}_{4}$
(b) $\mathrm{HClO}{4}>\mathrm{HOCl}>\mathrm{HClO}{2}>\mathrm{HClO}_{3}$
(c) $\mathrm{HClO}{4}>\mathrm{HClO}{3}>\mathrm{HClO}_{2}>\mathrm{HOCl}$
(d) $\mathrm{HClO}{2}>\mathrm{HClO}{4}>\mathrm{HClO}_{3}>\mathrm{HOCl}$
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Solution:
- Decreasing order of strength of oxoacids
$$ \mathrm{HClO}{4}>\mathrm{HClO}{3}>\mathrm{HClO}_{2}>\mathrm{HOCl} $$
Reason Consider the structures of conjugate bases of each oxyacids of chlorine.
Negative charge is more delocalised on $\mathrm{ClO}{4}^{-}$due to resonance, hence, $\mathrm{ClO}{4}^{-}$is more stable (and less basic).
Hence, we can say as the number of oxygen atom(s) around $\mathrm{Cl}$-atom increases as oxidation number of $\mathrm{Cl}$-atom increases and thus, the ability of loose the $\mathrm{H}^{+}$increases.
