[fexaac]

Hello, I've been stuck on a question for a while now, and I would like to have someone else look at it.
The question is: "Sodium carbonate is added in small quantities to a solution containing Ni2+ ions with a molar concentration of 0.1 and Cu2+ ions with a molar concentration of 0.1. Calculate the concentration of the first ion which starts to precipitate when the second ion starts to precipitate as well. Ksp(NiCO3) = 1.4x10^-7, Ksp (CuCO3) = 2.5x10^-10".
The way I've solved this particular question has given me an unsual answer, but basically what I've done was to calculate the concentration of the carbonate ion needed in order to make CuCO3 precepitate and then use the same concentration to calculate the concentration of Ni2+ions as requested. The result I've got is 56 M.
Can someone please tell me if I answered correctly or if I did something wrong? The result just doesn't seem right and I can't seem to find an answer on any of my Chemistry books.
Thank you very much.

[Borek]

Something is definitely wrong.

Hard to tell where you went wrong without seeing what you did.

[mjc123]

Wrong way round. CuCO₃ will precipitate first, as it has the lower solubility product. Calculate the concentration of carbonate needed to start precipitating Ni²⁺. What is the concentration of Cu²⁺ in equilibrium with this?