Question

What is the solubility (in mol/L) of $Fe{\left(OH\right)}_3$ in a solution of $pH=8.0$? [$K_{sp}$ for $Fe{\left(OH\right)}_3=1.0\times {10}^{-36}$]

• A. ${10}^{-9}M$
• B. ${10}^{-12}M$
• C. ${10}^{-16}M$
• D. ${10}^{-18}M$

Answer 1

Answer: (D)

${10}^{-18}M$

$pOH=14.0-pH=14.0-8.0=6.0$

$\left[O{H}^{-}\right]={10}^{-pOH}={10}^{-6}$

$K_{sp}=\left[F{e}^{3+}\right][O{H}^{-}{]}^3$

$1.0\times {10}^{-36}=\left[F{e}^{3+}\right]\times ({10}^{-6}{)}^3$

Solubility of $Fe(OH{)}_3=[F{e}^{3+}]=1.0\times {10}^{-18}M$