Question

What is the solubility of Al(OH)3, (Ksp = 1 × 10–33) in a buffer solution pH = 4 ?

• A. 10–3 M
• B. 10–6 M
• C. 10–4 M
• D. 10–10 M.

Answer 1

Answer: (A)

10–3 M

Answer 2

pH = 4 $\Rightarrow$ [H+] = 10–4 M

$\Rightarrow$ [OH–] = 10–10 M

Al (OH)3 $\rightleftharpoons$ Al+3 + 3 OH–

Ksp (Al (OH)3) = [Al+3] [OH–]3

[Al3+] [OH–]3 = 1 × 10–33

[Al3+] (10–10)3 = 1 × 10–33

$\Rightarrow$ [Al+3] = 10–3 M