Question

In the following reaction,

$Fe\left(OH{)}_3\right(s)\leftrightharpoons F{e}^{3+}(aq)+3O{H}^{-}(aq)$

What is the solubility product expression for the saturated solution when the ionic solid $Fe(OH{)}_3$ is added to water and dissociates into its component ions?

• A. $K_{sp}=\frac{\left[F{e}^{3+}\right][O{H}^{-}{]}^3}{\left[Fe\right(OH{)}_3]}$
• B. $K_{sp}=\left[F{e}^{3+}\right]\left[3O{H}^{-}\right]$
• C. $K_{sp}=\left[F{e}^{3+}\right][O{H}^{-}{]}^3$
• D. $K_{sp}=\left[F{e}^{3+}\right]\left[O{H}^{-}\right]$

Answer 1

The correct option is C $K_{sp}=\left[F{e}^{3+}\right][O{H}^{-}{]}^3$

The solubility product expression is as shown.
$K_{sp}=\left[F{e}^{3+}\right][O{H}^{-}{]}^3$
Note: In the above expression, the term $\left[Fe\right(OH{)}_3]$ does not appear as, $Fe(OH{)}_3$ is a solid and the concentration of solids do not appear in the solubility product expression.