Question

At $30^\circ\text{C}$ the solubility of $\text{PbI}_2$ salt in $2\text{ M KI}$ solution will be X, if the solubility product of $\text{PbI}_2$ at $30^\circ\text{C}$ is $4\times10^{-9}$. Identify the value of X.

• A. $3.0\times10^{-8}\text{ M}$
• B. $2.4\times10^{-8}\text{ M}$
• C. $4.8\times10^{-7}\text{ M}$
• D. $6.0\times10^{-7}\text{ M}$

Hint:

The common ion effect simplifies the math significantly! By approximating the total common ion concentration to just the value from the strong electrolyte source ($0.2\text{ M}$), you avoid a cubic equation. The calculation reduces to a simple division: $X = \frac{K_{\text{sp}}}{(0.2)^2} = \frac{2.4 \times 10^{-9}}{0.04} = 6.0 \times 10^{-7}\text{ M}$.

Answer 1

The Correct Option is D