Question

The solubility product of a salt having general formula MX2, in water is : 4 × 10–12. The concentration of M2+ ions in the saturated aqueous solution of the salt is :

• A. 2.0 × 10–6 M
• B. 1.0 × 10–4 M
• C. 1.6 × 10–4 M
• D. 4.0 × 10–10 M

Answer 1

Answer: (B)

1.0 × 10–4 M

Answer 2

MX2(s) $\rightleftharpoons$ M2+ (aq) + 2X– (aq)

Ksp = s . (2s)2 = 4s3 $\Rightarrow$ 4 × 10–12 = 4s3

$\Rightarrow$ s3 = 1 × 10–12

$\Rightarrow$s = 1 × 10–4 M $\Rightarrow$ [M2+] = 1 × 10–4 M