I think the trouble is two-fold.
1. I believe you are trying to calculate Ksp and not solubility or S.
2. You have not taken into account the increased solubility due to the acidity.
Your equations look good. But notice the following.
..........ZnCO3 ==> Zn^2+ + CO3^2-
and CO3^2- + H^+ ==> HCO3^-
and HCO3^- + H^+ ==> H2CO3
As the acidity increases it reduces the CO3^2- according to Le Chatelier's Principle (the CO3^2- is shifted to the right) and the HCO3^- is shifted to the right. That makes CO3^2- from ZnCO3 too small so the solubility of ZnCO3 increases to make up the difference.
I think the easiest way to do these is as follows:
I can't write Greek symbols so let's let a2 = alpha 2 = (CO3^2-).
Then a2 = (CO3^2-) = k1k2/D where D is the denominator and =
(H^+)^2 + k1(H^+) + k1k2
So plug in H^+, k1 and k2 for H2CO3 and solve for the k1k2/D term. Then
...........ZnCO3 ==> Zn^2+ + CO3^2-
I..........solid.......0.......0
C..........solid.......S......S*a2
E.........solid........S......S*a2
and solve for S.
If you need further assistance, please post your work and especially show what you are using for Ksp, k1 and k2.
What is the solubility of ZnCO3 at 25C in a buffer solution with a pH of 10.21?
ZnCO3 <----> Zn++ + CO3 – -
CO3-- + H2O ----> HCO3- + OH-
pOH = 14 – 10.21 = 3.79
[OH-] = 1.62x10^-4 M = [CO3--] = [Zn++]
Ksp = [Zn++][CO3-] = (1.62x10^-4)( 1.62x10^-4) =
2.63x10^-8
when i input my answer in my homework it says that its incorrect
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