Question

Calculate the solubility of MnCO₃ (a) in pure water and (b) in a solution in which [CO₃^2-] = 0.285 M.

Solubility in pure water = ______M

Solubility in 0.285 M CO₃^2- = ______M

Answer 1

The Ksp of manganese(II) carbonate, MnCO3, is 2.42*10^-11

a)

At equilibrium:

MnCO3 ----> Mn2+ + CO32-

   s s

Ksp = [Mn2+][CO32-]

2.42*10^-11=(s)*(s)

2.42*10^-11= 1(s)^2

s = 4.92*10^-6 M

Answer: 4.92*10^-6 M

b)

[CO32-] = 0.285 M

At equilibrium:

MnCO3 ----> Mn2+ + CO32-

   s 0.285 + s

Ksp = [Mn2+][CO32-]

2.42*10^-11=(s)*(0.285+ s)

Since Ksp is small, s can be ignored as compared to 0.285

Above expression thus becomes:

2.42*10^-11=(s)*(0.285)

2.42*10^-11= 1(s)^1 * 0.285

s = 8.49*10^-11 M

Answer: 8.49*10^-11 M