Question

Which among the following does not disproportionate in the alkaline medium?
${\mathrm{F}}_2,{\mathrm{Cl}}_2,{\mathrm{S}}_8,{\mathrm{P}}_4$

Answer 1

Disproportionation reaction

• Disproportionation reactions are a special type of redox reaction.
• In a disproportionation reaction, an element in one oxidation state is simultaneously oxidized and reduced.

Disproportionate in the alkaline medium

• In ${\mathrm{Cl}}_2$, oxidation state of Cl is 0 so it can give a disproportionation reaction because $\mathrm{Cl}$ shows the oxidation state from $-1\text{to}+7$.

$$\begin{gathered} {\text{Cl}}_{\text{2}}{\text{(g) + 2 OH}}^{\text{–}}{\text{(aq) → ClO}}^{\text{–}}{\text{(aq) + Cl}}^{\text{–}}{\text{(aq) + H}}_{\text{2}}\text{O (l)} \\ 0+1-1 \end{gathered}$$

• Fluorine cannot exhibit a positive oxidation state and hence does not show disproportionation tendency.
• Fluorine can exhibit only $-1$ oxidation state.
• The disproportion reaction of ${\mathrm{S}}_8$ is as follows:-

$$\begin{gathered} {\text{S}}_{\text{8}}{\text{(s) + 12 OH}}^{\text{–}}{\text{(aq) → 4S}}^{2-}{\text{(aq) + 2S}}_{\text{2}}{\text{O}}_3^{2-}{\text{(aq) + 6H}}_{\text{2}}\text{O(l)} \\ 0-2+2 \end{gathered}$$

• The disproportion reaction of ${\mathrm{P}}_4$ is as follows:-
• $$\begin{gathered} {\mathrm{P}}_4\left(\mathrm{s}\right)+3{\mathrm{OH}}^{–}\left(\mathrm{aq}\right)+3{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to {\mathrm{PH}}_3\left(\mathrm{g}\right)+3{\mathrm{H}}_2{\mathrm{PO}}_2^{-}\left(\mathrm{aq}\right) \\ 0-3+1 \end{gathered}$$

Hence, ${\mathrm{F}}_2$ does not disproportionate in the alkaline medium.