Answer:
[tex][H_3O^+]=6.8*10^{-22}[/tex]
Explanation:
For a solution with [tex][Pb^{+2}]=1*10^{-6}[/tex] :
[tex]Kps=[Pb^{+2}]*[S^{-2}]=3.4*10^{-28}[/tex]
[tex]1*10^{-6}*[S^{-2}]=3.4*10^{-28}[/tex]
[tex][S^{-2}]=3.4*10^{-22}[/tex]
For the iron ions:
[tex]Kps=[0.365]*[S^{-2}]=3.7*10^{-19}[/tex]
[tex][S^{-2}]=1.01*10^{-18}[/tex]
Given that the [tex][S^{-2}][/tex] concentration required to start precipitating iron is higher than the final concentration for the Pb precipitation (when the desired concentration is reached), the iron will not precipitate.
The concentration of [tex]H_3O^+[/tex]
[tex]H_2S + 2 H_2O \longrightarrow 2 H_3O^+ + S^{-2}[/tex]
[tex][H_3O^+]=2*[S^{-2}]=6.8*10^{-22}[/tex]
