[repetelww]

The problem that I have been tasked to solve reads as follow:

Determine the solubility of MgCO3 in 0.01M Na2CO3 in water at a pH of 10.00.

My preliminary calculations are attached, but I cannot shake the feeling that I am forgetting something that is pertinent to the problem, but I just cannot see it. Any pointers or assistance would be so greatly appreciated.

Good Day to all.

[Borek]

I just skimmed, and it looks OK to me.

[repetelww]

Thank you for the rapid response. The question is bothering me, because it almost seems that the method neglects the common ion effect of the carbonate from the Na2CO3 solution. The problem seems to hinge on the common ions from the solution. It is really troubling, would you happen to know how to reconcile the problem I am having with the common ion effect in this particular case?

[Borek]

Sorry, my mistake, I misread the problem. You are perfectly right.

Thing that you have to change is to calculate concentration of CO₃^2- from the presence of sodium carbonate (using similar K_a2 based approach you already used). Just add this concentration to the CO₃^2- concentration from MgCO₃ dissolution in the final step, where you plug the [Mg²⁺] and [CO₃^2-] into K_sp.

And I hope I am right this time.