When excess oxalic acid is added to solution, is precipitated and the solution still contains some u — Ionic Equilibrium Chemistry Question

💡 Solution & Explanation

The precipitation reaction is $\text{Ca}^{2+} + \text{H}_2\text{C}_2\text{O}_4 \rightleftharpoons \text{CaC}_2\text{O}_4(s) + 2\text{H}^+$. As precipitation occurs, hydrogen ions are released, increasing the acidity of the solution. According to Le Chatelier's principle and the common ion effect, this buildup of $\text{H}^+$ strongly suppresses the further ionization of the weak oxalic acid, which limits the available $\text{C}_2\text{O}_4^{2-}$ preventing the complete precipitation of $\text{Ca}^{2+}$. Therefore, correct answer is C.