Question

Calculate the molar solubility of MX2, if the Ksp=3.3x10^-8

how can i solve this problem?

Answer 1

Hi roseanne,

First, we write out the equation when MX2 dissolves in water (or a suitable solvent):
MX2 --> (reversible arrow) M2+ + 2X-

So Ksp = [M2+][X-]^2

Solubility would refer to the concentration of an ion produced in 1:1 ratio with the original solid. In this case, we can take [M2+] to be the solubility since M2+ is in a 1:1 ratio with MX2. Note that we CANNOT use [X-] as the solubility since X- is in a 2:1 ratio with MX2.

So we let [M2+] = x
Now [X-] = 2x since ratio of M2+:X- = 1:2
So Ksp = (x)(2x)^2 = 4x^3 = 3.3X10^-8

Then x = solubility = 0.00202M.

Hope I helped! (:

-J

Answer 2

that helped a lot, thanks!