Question

The molar solubility of CoS is 5.0 x 10-22 mol l-1 in pure water. Calculate the Ksp for Cos.

A-1.6 × 10-35
B-2.5x 10-43
C-4.7 x 10-6
D-5.0 x 10-22
E-2.2 x 10-11

Answer 1

B

Step-by-step explanation:

Write the dissociation reaction of solid CoS:

`\displaystyle \text{CoS}_\text{(s)} \rightleftharpoons \text{Co}_\text{(aq)}^(2+) + \text{S}_\text{(aq)}^(2-)`

The Ksp expression is hence:

`\displaystyle K_(sp) = [\text{Co}^(2+)][\text{S}^(2-)]`

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:

`\displaystyle \begin{aligned} K_(sp) & = [\text{Co}^(2+)][\text{S}^(2-)] \\ \\ & = (5.0* 10^(-22))^2 \\ \\ & = 2.5* 10^(-43)\end{aligned}`

In conclusion, the answer is B.