Question

Calculate the solubulity and molar solubility of CaF2 at 25 degrees celsius in a solution of 0.0100 M NaF. Ksp(CaF2)= 3.9e-11

Answer 1

NaF ----------------------> Na+    + F-

0.01                              0.01       0.01

CaF2 ----------------------------> Ca+2   + 2F-

                                              S            2S -------------------------------> in water

                                             S            2S + 0.01 -----------------------> in presence of NaF

                                            S             0.01 -----------------------> in presence of NaF (S can be neglected NaFis strong )

Ksp = [Ca+2][F-]^2

3.9 x 10^-11 = [Ca+2] (0.01)^2

3.9 x 10^-11 = S x (0.01)^2

S= 3.9 x 10^-7 M

molar solubility of CaF2 = S = 3.9 x 10^-7 M