Calculate the solubility in moles/L of the following salts c) FeS Ksp = 3.7 x 10-19 FeS =gt; Fe2+ + S2- Ksp = [Fe2+][HS-][OH-] 3.7 x 10-19 = (S)3 S…

Calculate the solubility in moles/L of the following salts

c) FeS Ksp = 3.7 x 10-19    FeS => Fe2+ + S2-Ksp = [Fe2+][HS-][OH-]3.7 x 10-19 = (S)3S = (3.7 x 10-19)1/3S = 7.2 x 10-7 M

Can anybody please explain where OH- comes from ?