Question

A (2.1x10^-1) M Na2SO4 is also saturated with Ag2SO4. The [Ag+] is (9.30x10^-3) M. What is the value of Ksp for Ag2SO4 at this temperature?

Answer 1

Na2SO4 dissociates completely as:
Na2SO4 -----> 2Na+   + SO42-
so,
[SO42-] = 2.1*10^-1 M = 0.21 M
SO42- from Ag2SO4 will be less as Ag2SO4 is weak electrlolyte and hence it can be ignored as compared to above one
Now:
Ag2SO4   ---> 2Ag+   +   SO42-
                          9.30*10^-3    0.21
Ksp = [Ag+]^2 [ SO42-]
        = (9.30*10^-3)^2 * 0.21
         = 1.82*10^-5 M
Answer: 1.82*10^-5 M