Question

What is the minimum pH when Fe(OH)3 starts precipitating from a solution containing 0.1M FeCl3? Ksp of Fe(OH)3 = 8 × 10–13 M3

• A. 3.7
• B. 5.7
• C. 10.3
• D. 8.3

Answer 1

Answer: (C)

10.3

Answer 2

[Fe3+] [OH–]3 Ksp

[OH–] $\geq$ 3.7 $\Rightarrow$ pOH $\leq$ 3.7

$\Rightarrow$ pH $\geq$ 10.3.