Is it [OH]^2 = 1.2e-11/.001
The other approach is when we try to calculate concentrations in saturated solution.
Say, we have PbCl2
and we know
How do we find how much PbCl2
dissolved? Let's say solubility is x mol/L. That means saturated solution contains x mol/L of Pb2+
, but - because of the stoichiometry - twice as much Cl-
] = x
] = 2x
Now plug these into the Ksp and you will see where these strange coefficients come from.