Which of the following species acts as both bronsted acid and base?
Which of the following species acts as both bronsted acid and base?
$\mathrm{OH}^{-}$
$\mathrm{NH}_3$
$\mathrm{NaCl}$
$\mathrm{HSO}_4^{-}$
Solution
A Bronsted-Lowry acid is a proton $\left(\mathrm{H}^{+}\right.$ion) donor while Bronsted-Lowry base is a proton $\left(\mathrm{H}^{+}\right.$ ion) acceptor.
$\mathrm{HSO}_4^{-}+\mathrm{H}_2 \mathrm{O} \rightleftharpoons \mathrm{H}_2 \mathrm{SO}_4+\mathrm{OH}^{-}$(Bronsted based)
$\mathrm{HSO}_4^{-}+\mathrm{H}_2 \mathrm{O} \rightleftharpoons \mathrm{SO}_4^{2-}+\mathrm{H}_3 \mathrm{O}^{+} \quad$ (Bronsted acid)
$\mathrm{HSO}_4^{-}$act as a conjugate base of sulphuric acid and does not give $\mathrm{H}^{+} . \mathrm{SO}_4^{2-}$ is a conjugate base of $\mathrm{HSO}_4^{-}$ and does not get ionised further. Thus, $\mathrm{HSO}_4^{-}$is Bronsted acid as well as Bronsted base.