Question

Calcium carbonate is an "insoluble salt". But the solubility of CaCO3 can be increased substantially by acidifying the solution. Write all the relevant equilibrium equations and explain why adding acid will increase the solubility of calcium carbonate.

Answer 1

Answer:

$CO_{3}^{2-}$ is converted to $H_{2}CO_{3}$ in acidic solution.

Explanation:

• $CaCO_{3}$ dissociates in solution to produce $Ca^{2+}$ and $CO_{3}^{2-}$ ions.

          Reaction: $CaCO_{3}\rightleftharpoons Ca^{2+}+CO_{3}^{2-}$

• $CO_{3}^{2-}$ is a strong conjugate base of weak acid $H_{2}CO_{3}$.
• When acid is added to a solution of $CaCO_{3}$, $CO_{3}^{2-}$ readily consumes two equivalent of $H^{+}$ and gets converted to $H_{2}CO_{3}$.
• Reaction: $2H^{+}+CO_{3}^{2-}\rightleftharpoons H_{2}CO_{3}$
• So, $CaCO_{3}$ dissociated more in acidic solution to produce more $CO_{3}^{2-}$ and keeps solubility product same at a given temperature.
• Hence, solubility of $CaCO_{3}$ increases when acid is added.