Answer
$HCO_{3}^{-}(aq) + HS^-(aq) \rightleftharpoons CO_{3}^{2-}(aq) + H_{2}S(aq)$
Here, $HCO_{3}^{-}(aq)$ is the acid and $HS^-(aq)$ is the base.
$HCO_{3}^{-}(aq) + HS^-(aq) \rightleftharpoons H_{2}CO_{3}(aq) + S^{2-}(aq)$
Here, $HCO_{3}^{-}(aq)$ is the base and $HS^-(aq)$ is the acid.
Work Step by Step
According to the definition,
Acid: proton ($H^{+}$ ion) donor
Base: proton ($H^{+}$ ion) acceptor
In the first reaction, $HCO_{3}^{-}$ is an acid because it donates a proton.
$HS^-$ is a base because it accepts the proton.
In the second reaction, $HS^-$ is an acid because it donates a proton.
$HCO_{3}^{-}$ is a base because it accepts the proton.
