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

Explanation has been given below.

Step-by-step 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.