Polyprotic salts containing amphiprotic anions (e.g., , ) exhibit unique pH behavior. Which of the f — Ionic Equilibrium Chemistry Question

💡 Solution & Explanation

Amphiprotic anions like $HCO_3^-$ can undergo ionization ($HCO_3^- \rightleftharpoons H^+ + CO_3^{2-}$, governed by $K_{a2}$) and hydrolysis ($HCO_3^- + H_2O \rightleftharpoons H_2CO_3 + OH^-$, governed by $K_{a1}$). The exact mathematical derivation yields $[H^+] = \sqrt{K_{a1} \cdot K_{a2}}$, which strictly simplifies to $pH = \frac{pK_{a1} + pK_{a2}}{2}$. Thus, the pH is fundamentally independent of concentration, and it relies on both constants, not solely $K_{a2}$.