Statement-I : $\mathrm{H}_3 \mathrm{PO}_4$ is a stronger acid than $\mathrm{H}_2 \mathrm{PO}_4^{-}$.

Question

Statement-I : $\mathrm{H}_3 \mathrm{PO}_4$ is a stronger acid than $\mathrm{H}_2 \mathrm{PO}_4^{-}$. Statement-II : $\mathrm{p} K_{a_1}$ is greater than $\mathrm{p} K_{a_2}$ for $\mathrm{H}_3 \mathrm{PO}_4$.

Professor PC Thomas Classes · Answer

(b) : $\mathrm{H}_3 \mathrm{PO}_4 ightleftharpoons \mathrm{H}^{+}+\mathrm{H}_2 \mathrm{PO}_4^{-} ; \quad K_{a_1}$  \ $ \mathrm{H}_2 \mathrm{PO}_4^{-} ightleftharpoons \mathrm{H}^{+}+\mathrm{HPO}_4^{2-} ; \quad K_{a_2} $ $\mathrm{H}^{+}$and $\mathrm{H}_2 \mathrm{PO}_4^{-}$ \ are having stronger ion-pair attraction. Hence, $K_{a_2}<K_{a_1}$ and $\mathrm{p} K_{a_2}>\mathrm{p} K_{a_1}$.