Chapter 15, Problem 98E

A solution of 0.075 M CoBr₂ is saturated with ${\text{H}}_{\text{2}}\text{S}\left(\left[{\text{H}}_{\text{2}}\text{S}\right]=0.\text{1}0M\right)$. What is the minimum pH at which CoS begins to precipitate?.

$\text{CoS}\left(s\right)\rightleftharpoons {\text{Co}}^{2+}\left(aq\right)+{\text{S}}^{2-}\left(aq\right)$ $K_{\text{sp}}=4.5\times {10}^{-27}$

${\text{H}}_2\text{S}\left(aq\right)+2{\text{H}}_2\text{O}\left(l\right)\rightleftharpoons 2{\text{H}}_3{\text{O}}^{+}\left(aq\right)+{\text{S}}^{2-}\left(aq\right)$ $K=1.0\times {10}^{-26}$