# Question #399f7

##### 1 Answer
May 27, 2017

Add more acetic acid (HOAc)

#### Explanation:

Adding acid into an aqueous solution functions to deliver hydronium ions $\left({H}_{3} {O}^{+}\right)$ into the solution. If ions of Calcium and Carbonate are present, Hydrogen ions $\left({H}^{+}\right)$ from the ${H}_{3} {O}^{+}$ will coordinate (bond) with the carbonate ion $\left(C {O}_{3}^{2 -}\right)$ forming the weak acid 'Hydrogen Carbonate' $\left({\left(H - C {O}_{3}\right)}^{-}\right)$.

Hydrogen Carbonate is no longer part of the Calcium Carbonate Equilibrium which is now deficient in carbonate ions on the product side of the equilibrium.

$C a C {O}_{3}$ $r i g h t \le f t h a r p \infty n s C {a}^{2 +} + C {O}_{3}^{2 -}$ => $C a C {O}_{3} \implies C {a}^{2 +} + \left(_\right)$

Additional unionized Calcium Carbonate then ionizes in order to replace the $C {O}_{3}^{2 -}$ that combined with ${H}^{+}$ from the acetic acid.

This is typically described by saying "the equilibrium
$C a C {O}_{3}$ $r i g h t \le f t h a r p \infty n s C {a}^{2 +} + C {O}_{3}^{2 -}$ shifts to the right increasing solubility of the $C a C {O}_{3}$".