The amphiprotic bicarbonate anion () is governed by two simultaneous mechanisms in water: ionization — Ionic Equilibrium Chemistry Question

💡 Solution & Explanation

As an amphiprotic species, $HCO_3^-$ can act as an acid or a base. Its ionization mechanism (acting as an acid) is $HCO_3^- + H_2O \rightleftharpoons CO_3^{2-} + H_3O^+$. Its hydrolysis mechanism (acting as a base by accepting a proton from water) is $HCO_3^- + H_2O \rightleftharpoons H_2CO_3 + OH^-$. The latter relies on the $K_{a1}$ of the parent acid $H_2CO_3$ because it forms $H_2CO_3$.