## General Chemistry: Principles and Modern Applications (10th Edition)

A conjugate acid-base has only one $H^+$ as a difference. To check this description, take the acid and write its reaction: (a) $HCO_3^-(aq) + H_2O(aq)$ $CO_3^{2-}(aq) + H_3O^+(aq)$ As we can see, we get $CO_3^{2-}$, so $HCO_3^-$ is its conjugate base. But, if the result is different: (b) $HSO_3^-(aq) + H_2O(aq)$ $SO_3^{2-}(aq) + H_3O^+(aq)$ $SO_3^{2-} \ne SO_4^{2-}$, so they are not a conjugate acid-base pair.