Question

The common ion effect for ionic solids (salts) is to decrease the solubility of the ionic compound in water significantly. Explain the common ion effect in detail.

Answer 1

Answer:

Explanation has been given below.

Explanation:

Let's consider solubility equilibrium of an ionic insoluble compound e.g. $BaSO_{4}$

$BaSO_{4}\rightleftharpoons Ba^{2+}+SO_{4}^{2-}$

Equilibrium constant of this solubility equilibrium is represented in terms of solubility product ($K_{sp}$) which is expressed as-

$K_{sp}=[Ba^{2+}][SO_{4}^{2-}]$

Now, if we add an ionic salt e.g. $Na_{2}SO_{4}$ with a common ion $SO_{4}^{2-}$ then concentration of $SO_{4}^{2-}$ increases.

But, at a constant temperature, $K_{sp}$ is constant.

Therefore, to keep $K_{sp}$ constant, excess amount of $SO_{4}^{2-}$ will combine with free $Ba^{2+}$ ion in solution and produce $BaSO_{4}$.

Hence, as a whole, solubility of $BaSO_{4}$ decreases.