MgF2 --------> Mg+2 (aq) + 2F- (aq)
                      Â
s               Â
2s
Ksp   =
[Mg+2][F-]2
6.4*10-9Â Â = s*(2s)2
6.4*10-9Â Â Â Â = 4s3
s3Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â
= 1.6*10-9
s             Â
= 1.17*10-3 M
solubility of mgF2 is 1.17*10-3 M
MgF2 --------> Mg+2 (aq) + 2F- (aq)
                      Â
s               Â
2s
                      Â
s               Â
0.05 +2s
Ksp   =
[Mg+2][F-]2
6.4*10-9Â Â = s*(2s+0.05)2
   Â
s           Â
= 2.6*10-6 M
solubility of MgF2 in NaF is 2.6*10-6 M