Question

Which of the following can be classified as autoprotolysis reactions?

• A. $H_{2}O\left(l\right)+H_{2}O\left(l\right)\rightleftharpoons H_3{O}^{+}\left(aq\right)+O{H}^{-}\left(aq\right)$
• B. $2N{H}_3\left(l\right)\rightleftharpoons N{H}_4^{+}\left(aq\right)+N{H}_2^{-}\left(aq\right)$
• C. $C{H}_{3}COOH\left(aq\right)\rightleftharpoons C{H}_{3}CO{O}^{-}\left(aq\right)+H^{+}\left(aq\right)$
• D. $2C{H}_{3}COOH\left(l\right)\rightleftharpoons C{H}_{3}CO{O}^{-}\left(aq\right)+C{H}_{3}COO{H}_2^{+}\left(aq\right)$

Answer 1

Answer: (A), (B), (D)

The correct options are
A $H_{2}O\left(l\right)+H_{2}O\left(l\right)\rightleftharpoons H_3{O}^{+}\left(aq\right)+O{H}^{-}\left(aq\right)$
B $2N{H}_3\left(l\right)\rightleftharpoons N{H}_4^{+}\left(aq\right)+N{H}_2^{-}\left(aq\right)$
D $2C{H}_{3}COOH\left(l\right)\rightleftharpoons C{H}_{3}CO{O}^{-}\left(aq\right)+C{H}_{3}COO{H}_2^{+}\left(aq\right)$

Self ionization or auto - protolysis :
The phenomenon in which Proton transfer is occurring between two identical molecules is known as self ionization.
For example - $\underset{BronstedAcid}{H_{2}O}\left(l\right)+\underset{BronstedBase}{H_{2}O}\left(l\right)\rightleftharpoons \underset{ConjugateAcid}{H_3{O}^{+}}\left(aq\right)+\underset{ConjugateBase}{O{H}^{-}(aq})$

In the above example , $H_{2}O$ acts both as a Bronsted base and a Bronsted acid and consequently conjugate acid $H_3{O}^{+}$ and conjugate base $O{H}^{-}$ are formed.