Explain the common ion effect on the solubility of salts.

(N/A) The solubility of a sparingly soluble salt is decreased in the presence of a common ion. $A$ common ion effect occurs when the concentration of either the cation or the anion of the salt increases in the solution.
$1$. In a saturated solution of $AgCl$,if $NaCl$ is added,the $Cl^{-}$ ion is common. If $AgNO_{3}$ is added,the $Ag^{+}$ ion is common. According to Le Chatelier's principle,the increase in the concentration of these ions shifts the equilibrium $AgCl_{(s)} \rightleftharpoons Ag^{+}_{(aq)} + Cl^{-}_{(aq)}$ to the left,causing precipitation and decreasing the solubility of the salt.
$2$. Similarly,in a saturated solution of $NaCl$,if $HCl$ gas is passed,the concentration of $Cl^{-}$ increases,which forces the equilibrium $NaCl_{(s)} \rightleftharpoons Na^{+}_{(aq)} + Cl^{-}_{(aq)}$ to shift to the left,resulting in the precipitation of solid $NaCl$ and a decrease in its solubility.