Question

Only 0.0640 grams of PbF2 will dissolve in 100.0 mL of solution. From this data, calculate the Ksp by two methods.

Answer 1

Which method do you know?

Answer 2

Ksp=produts molarity/reatants molarity

Answer 3

Then you dont know either.
mols PbF2 dissolved - 0.064/molar mass PbF2 = Estimated 0.0004
............PbF2(s) ==> Pb^2+ + 2F^-
I..........solid.................0............0
C.........solid............0.0004.....0.0008
E.........solid............0.0004......0.0008

Ksp = (Pb^2+)(F^-)^2
Ksp = (0.0004)(0.0008)^2 = ?

Another method.
............PbF2 ==> Pb^2+ + 2F^-
I..........solid...........0..............0
C.........solid...........x..............2x
E.........solid...........x..............2x
Ksp = (Pb^2+)(F^-)^2
Ksp = (x)(2x)^2 = 4x^3
You know x = estimated 0.0004 so
Ksp = 4*0.0004)^3 approximately.
Don't forget to get more accurate numbers