# Problem: Iron concentrations greater than 5.4 × 10–6 M in water used for laundry purposes can cause staining. What [OH–] is required to reduce [Fe2+] to this level by precipitation of Fe(OH)2?

###### FREE Expert Solution

Fe(OH)2(s)  Fe2+(aq) + 2 OH(aq)

The Ksp expression for Fe(OH)2 is:

${\mathbf{K}}_{\mathbf{sp}}\mathbf{=}\mathbf{\left[}{\mathbf{Ba}}^{\mathbf{2}\mathbf{+}}\mathbf{\right]}\mathbf{\left[}{{\mathbf{SO}}_{\mathbf{4}}}^{\mathbf{2}\mathbf{-}}\mathbf{\right]}\phantom{\rule{0ex}{0ex}}\mathbf{8}\mathbf{.}\mathbf{0}\mathbf{×}{\mathbf{10}}^{\mathbf{-}\mathbf{16}}\mathbf{=}\mathbf{\left(}\mathbf{5}\mathbf{.}\mathbf{4}\mathbf{×}{\mathbf{10}}^{\mathbf{-}\mathbf{6}}\mathbf{\right)}{\mathbf{\left(}\mathbf{2}\mathbf{x}\mathbf{\right)}}^{\mathbf{2}}\phantom{\rule{0ex}{0ex}}\mathbf{8}\mathbf{.}\mathbf{0}\mathbf{×}{\mathbf{10}}^{\mathbf{-}\mathbf{16}}\mathbf{=}\mathbf{\left(}\mathbf{5}\mathbf{.}\mathbf{4}\mathbf{×}{\mathbf{10}}^{\mathbf{-}\mathbf{6}}\mathbf{\right)}\mathbf{4}{\mathbit{x}}^{\mathbf{2}}\phantom{\rule{0ex}{0ex}}\frac{\mathbf{8}\mathbf{.}\mathbf{0}\mathbf{×}{\mathbf{10}}^{\mathbf{-}\mathbf{16}}}{\mathbf{2}\mathbf{.}\mathbf{16}\mathbf{×}{\mathbf{10}}^{\mathbf{-}\mathbf{5}}}\mathbf{=}\frac{\overline{)\mathbf{2}\mathbf{.}\mathbf{16}\mathbf{×}{\mathbf{10}}^{\mathbf{-}\mathbf{5}}}{\mathbf{x}}^{\mathbf{2}}}{\overline{)\mathbf{2}\mathbf{.}\mathbf{16}\mathbf{×}{\mathbf{10}}^{\mathbf{-}\mathbf{5}}}}\phantom{\rule{0ex}{0ex}}$

###### Problem Details

Iron concentrations greater than 5.4 × 10–6 M in water used for laundry purposes can cause staining. What [OH] is required to reduce [Fe2+] to this level by precipitation of Fe(OH)2?