Question

In which of the following solutions will CaF2 be least soluble?

0.10 M Ca(NO3)2

0.01 M NaF

0.001 M Na

0.010 M Ca(NO3)2

Answer 1

0.10 M Ca(NO3)2

0.010 M Ca(NO3)2

They are least solubel in CaF2 due to common ion effect.

CaF2 --------------. Ca^2+ (aq) + 2F^-

in 0.01MCa(NO3)2

Ksp   = [Ca^2+][F^-]^2

3.9*10^-11         = (0.01)*[F^-]^2

[F^-]^2           = 3.9*10^-11/0.01  

   [F^-]                 = 6.24*10^-5 mole/L

0.1M Ca(NO3)2

Ksp   = [Ca^2+][F^-]^2

3.9*10^-11         = (0.1)*[F^-]^2

[F^-]^2           = 3.9*10^-11/0.1  

   [F^-]             = 1.97*10^-5 mole/L

0.1M Ca(NO3)2 least soluble

0.1 M Ca(NO3)2 >>>>>answer