1、求OH-浓度
pOH = 2 ,C(OH-) = 0.01
2、求溶解度s
---------------Mg(OH)2 = Mg2+ + 2OH-
初: 0 0.01
平衡: s 0.01+ 2s ≈ 0.01
s *0.01^2 = Ksp
s = 5.61*10^-8 mol/L