Question

The species: $H_{2}O,HC{O}_3^{–},HS{O}_4^{–}$ and $N{H}_3$ can act both as Bronsted acids and bases. For each case give the corresponding conjugate acid and conjugate base.

Answer 1

Part 1. Conjugate base for Bronsted acid

Conjugate base of a Bronsted-Lowry acid is the species formed after an acid donates its proton. So, the conjugate bases will have a proton less.

$H_{2}O\to O{H}^{-}+H^{+}$

$HC{O}_3^{–}\to C{O}_3^{2-}+H^{+}$

$HS{O}_4^{–}\to S{O}_4^{2-}+H^{+}$

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

Part 2. Conjugate acid for Bronsted base

Conjugate acid of a Bronsted-Lowry base is the species formed after an acid accepts a proton. So, the conjugate acid will have one proton extra.

$O{H}^{-}+H^{+}\to H_{2}O$

$C{O}_3^{2-}+H^{+}\to HC{O}_3^{–}$

$S{O}_4^{2-}+H^{+}\to HS{O}_4^{–}$

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

Therefore, the corresponding conjugate acids and conjugate bases are-

Species	Conjugate Acid	Conjugate Base
$H_{2}O$	$H_3{O}^{+}$	$O{H}^{-}$
$HC{O}_3^{-}$	$H_{2}C{O}_3$	$C{O}_3^{2-}$
$HS{O}_4^{-}$	$H_{2}S{O}_4$	$S{O}_4^{2-}$
$N{H}_3$	$N{H}_4^{+}$	$N{H}_2^{-}$