Question

the solubility-product constant (ksp) for MgCO3 at 25 degrees celcius is 6.8 x 10^-6. what is the molar solubility of this substance in 0.22M MgCl2 at 25 degrees C?

Answer 1

MgCl2 here is Strong electrolyte

It will dissociate completely to give [Mg2+] = 0.22 M

At equilibrium:

MgCO3 <----> Mg2+ + CO32-

   0.22 +s s

Ksp = [Mg2+][CO32-]

6.8*10^-6=(0.22 + s)*(s)

Since Ksp is small, s can be ignored as compared to 0.22

Above expression thus becomes:

6.8*10^-6=(0.22)*(s)

6.8*10^-6= 0.22 * 1(s)^1

s = 3.091*10^-5 M

Answer: 3.1*10^-5 M