Question

The solubility of $Pb(OH)_2$ in water is $6.7 \times 10^{ - 6 } M$. Calculate the solubility of $ Pb(OH)_2$ in a buffer solution of $pH = 8$.

Answer 1

In water, $ K_{ sp } = 4 \, S^3 = 4 ( 6.2 \times 10^{ - 4 } )^3 $
$= 1.2 \times 10^{ - 15 } $
In buffer of $pH = 8, pOH = 6, [ OH^- ] = 10^{ - 6 } $
$ K_{ sp } = S \, [ OH^- ]^2 $
$S = \frac{ 1.2 \times 10^{ - 15 }}{ 10^{ - 12}} = 1.2 \times 10^{ - 3 } M $