Question

The solubility of $AgI$ in $NaI$ solutions is less than that in pure water because:

• A. $AgI$ forms complex with $NaI$
• B. of common ion effect
• C. solubility product of $AgI$ is less than that of $NaI$
• D. the temperature of the solution decreases

Answer 1

Answer: (B)

$AgI\rightleftharpoons A{g}^{+}+I^{-}$
$NaCl\to N{a}^{+}+I^{-}$

Sodium iodide is a strong electrolyte and is completely dissociated. This increases the iodide ion concentration in solution and suppresses the ionization of $AgI$. Hence, the solubility of $AgI$ decreases.

This is called common ion effect.