Question

According to Bronsted - Lowry's Acids and Bases concept, select the species which can act as an acid as well as a base ?

• A. $S{O}_4^{2-}$
• B. $S^{2-}$
• C. $HS{O}_4^{-}$
• D. $C{l}^{-}$

Answer 1

The correct option is C $HS{O}_4^{-}$

Bronsted - Lowry Acids and Bases : According to bronsted lowry theory, acid is a substance that is capable of donating a hydrogen ion H⁺ and bases are substance that are capable of accepting H⁺ ion.

Species which can accept as well as donate $H^{+}$ ion, can act both as acid and base.
$HS{O}_4^{-}$ can give one $H^{+}$ and form $S{O}_4^{2-}$ , so it can act as an acid. Again , $HS{O}_4^{-}$ by accepting one $H^{+}$ can form $H_{2}S{O}_4$. So, it can also act as a base. $HS{O}_4^{-}+H^{+}\rightleftharpoons H_{2}S{O}_{4}HS{O}_4^{-}\rightleftharpoons S{O}_4^{2-}+H^{+}$ .
But $S{O}_4^{2-}$ , $C{l}^{-}$ , $S^{2-}$ all can only act as a base because they do not have a donateable proton.