Question

What is the net effect of the common ion?

• A. It reduces the solubility of the solute in the solution.
• B. It reduces the increases of the solute in the solution.
• C. It causes more product to be made.
• D. It causes more ions to form.
• E. There is no net effect overall.

Answer 1

The correct option is A It reduces the solubility of the solute in the solution.

The net effect of the common ion is that it reduces the solubility of the solute in the solution.
The common ion effect is observed when the addition of an ion common to two solutes causes precipitation or reduces ionization.
Thus, if to a solution of weak electrolyte, a solution of strong electrolyte is added which furnishes an ion common to that furnished by the weak electrolyte, the ionization of the weak electrolyte is suppressed.
For example, ammonium hydroxide is a weak electrolyte and ionizes to a small extent to give ammonium ions and hydroxide ions.
$N{H}_{4}OH\rightleftharpoons N{H}_4^{+}+O{H}^{-}$
A strong electrolyte NaOH is added which furnishes hydroxide ions that are common ions. This suppresses the equilibrium for the dissociation of ammonium hydroxide.
$NaOH\to N{a}^{+}+O{H}^{-}$