Question

Explain the following with reasons:
(i) Chlorine displaces iodine from $KI$ solution but iodine does not displace bromine from $KBr$ solution. Why?
(ii) $Hg+H_{2}S{O}_4\to HgS{O}_4+H_2$
Above reaction is not possible.

Answer 1

(i) In halide displacement reaction, more electronegative (EN) halogen (Cl>Br>I) tends to displace a lesser EN halide from its solution. Therefore, more EN halogen acts as oxidising agent and form halide molecule. Hence, $Cl$ being more EN than $I$ will therefore oxidises $I^{-}$ to $I_2$ but $I$ being less EN than $Br$ will not oxidise ${Br}^{-}$.

(ii)This can be explained by reduction potential values (tendency to accept electron) of the respective ions as:

${Hg}^{2+}/Hg=0.79Vand{H}^{+}/H_2=0V$

as the tendency of $H^{+}$ to reduce to $H_2$ is smaller than that of ${Hg}^{2+}$, the reaction $Hg+H_{2}S{O}_4\to HgS{O}_4+H_2$

is not possible.