Question

Answer the following :

The solubility of a sparingly soluble salt gets affected in the presence of a soluble salt having one common ion. Explain.

Answer 1

i. The presence of a common ion affects the solubility of a sparingly soluble salt.

ii. Consider, the solubility equilibrium of AgCl,

\[\ce{AgCl_{(s)} ⇌ Ag^+_{ (aq)} + Cl^-_{ (aq)}}\]

The solubility product of AgCl is

K_sp = [Ag⁺][Cl^-]

iii. Suppose AgNO₃ is added to the saturated solution of AgCl. The salt AgNO₃ being a strong electrolyte dissociates completely in the solution.

\[\ce{AgNO_{3(aq)} -> Ag^+_{ (aq)} + NO^-_{3(aq)}}\]

iv. The dissociation of AgCl and AgNO₃ produce a common Ag⁺ ion. The concentration of Ag⁺ ion in the solution increases owing to complete dissociation of AgNO₃.

v. According to Le-Chatelier's principle, the addition of Ag⁺ ions from AgNO₃ to the solution of AgCl shifts the solubility equilibrium of AgCl from right to left. The reverse reaction in which AgCl precipitates is favoured until the solubility equilibrium is re-established.

vi. However, the value of K_sp remains the same since it is an equilibrium constant. Thus, the solubility of a sparingly soluble compound decreases with the presence of a common ion in solution.