Ncert Exercises & Solutions

2.27 If the solubility product of CuS is 6 × 10^–16, calculate the maximum molarity of CuS in aqueous solution.

Solubility product of CuS, Ksp = 6 × 10⁻¹⁶ Let

s be the solubility of CuS in mol L⁻¹.

$CuS \leftrightarrow {Cu}^{2 +} + S^{2 -}$
$s s$

Now, $K_{sp} = [{Cu}^{2 +}] [S^{2 -}]$

= s × s

= s²

Then, we have, $K_{sp} = s^{2} = 6 \times 10^{- 16}$

$\Rightarrow s = \sqrt{6 \times 10^{- 16}}$
$= 2.45 \times 10^{- 6} mol L^{- 1}$

Hence, the maximum molarity of CuS in an aqueous solution is 2.45 × 10⁻⁸ mol L⁻¹.