when ionic product just cross the solubility product then
precipitation start. here concentration of Pb 2+
1.592e-6 M, optium S2- concentration require = Ksp / [Pb 2+]
                                               Â
=Â Â 2.51e-27 / 1.592e-6 M
                                                Â
= 1.1 * 10-9M
now dissocation os H2S
              Â
H2S(aq) ↔ 2H+ (aq) + S2- (aq) K = 1.1x10-20
K = [H+ (aq)]2 [S2- (aq)] / [H2S(aq)]
[H+ (aq)]2 = ( 1.1x10-20 *0 .1 ) / 1.1 * 10-9 =
10-12
[H3O+] = 10-6 M
