Question

Which one of the following can act as Bronsted acid as well as Bronsted base?

• A. $C{H}_{3}CO{O}^{-}$
• B. $C{O}_3^{2-}$
• C. $HPO{4}^{2-}$
• D. $S{O}_4^{2-}$

Answer 1

The correct option is C $HPO{4}^{2-}$

Bonsted acids are species which has tendency to donate proton while Bonsted bases are species which has tendency to accept proton.
$HP{O}_4^{2-}\left(aq\right)+H^{+}\left(aq\right)\rightleftharpoons H_{2}PO{4}^{-}\left(aq\right)HP{O}_4^{2-}\left(aq\right)\rightleftharpoons H^{+}\left(aq\right)+P{O}_4^{3-}\left(aq\right)$
None of the other electrolytes have $H^{+}$ to donate.
Hence $HP{O}_4^{2-}\left(aq\right)$ can both accept as well as donate $H^{+}$. $SoHP{O}_4^{2-}$ acts both as Bronsted base and Bronsted acid.