Answer:
B
Explanation:
Write the dissociation reaction of solid CoS:
[tex]\displaystyle \text{CoS}_\text{(s)} \rightleftharpoons \text{Co}_\text{(aq)}^{2+} + \text{S}_\text{(aq)}^{2-}[/tex]
The Ksp expression is hence:
[tex]\displaystyle K_{sp} = [\text{Co}^{2+}][\text{S}^{2-}][/tex]
If the molar solubility of CoS is 5.0 × 10⁻²² mol L⁻¹ (M), then 5.0 × 10⁻²² M of Co²⁺ and S²⁻ also forms. Hence, the value of Ksp is:
[tex]\displaystyle \begin{aligned} K_{sp} & = [\text{Co}^{2+}][\text{S}^{2-}] \\ \\ & = (5.0\times 10^{-22})^2 \\ \\ & = 2.5\times 10^{-43}\end{aligned}[/tex]
In conclusion, the answer is B.
