Question

Calculate the solubility of ZnCO3 in a buffer solution with a pH of 9.83 and Ksp of 1.2x10^-10

Answer 1

In a NON-buffered solution, it is
....ZnCO3 ==> Zn^2+ + CO3^2-
I....solid....0........0
C....solid....S........S
E....solid....S........S
C....solid....S........S

where S is the solubility of ZnCO3. But in a buffered solution, not all of the anion is in the form of CO3^2-.
The fraction in the form of CO3^2- is alpha 2 = (k1k2/D) where
D = (H^+)^2 + k1(H^+) + k1k2 so
Ksp = (Zn^2+)(CO3^2-)
Ksp = (S)(alpha2*S)
Solve for S = solubility ZnCO3. You will need to look up k1 and k2 for H2CO3, you have pH and that gives you (H^+)