Question

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

(i)$HCO{O}^{-}$ (ii)$N{H}_3$ (iii)$O^{2-}$ (iv)$HS{O}_4^{-}$

• A. i and ii
• B. ii and iii
• C. ii and iv
• D. i and iv

Answer 1

The correct option is C ii and iv

In the Bronsted Lowry theory, an acid donates a proton and the base accepts it.

$HCO{O}^{-}$ and $O^{2-}$ has no ionisable $H$ atoms and therefore, cannot donate $H^{+}$ ion so cannot be acids.

$N{H}_3$ and $HS{O}_4^{-}$ both can accept a proton as well as donate a proton. So, are Bronsted acid and as well as a base.

• $N{H}_3+H^{+}\to N{H}_4^{+}$

$N{H}_3\to N{H}_2^{-}+H^{+}$

• $HS{O}_4^{-}+H^{+}\to H_{2}S{O}_4$

$HS{O}_4^{-}\to S{O}_4^{2-}+H^{+}$