Question about solubility

Feb 2020
1
0
Italy
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 Ni^2+ ions with a molar concentration of 0.1 and Cu^2+ 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 Ni^2+ 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.
 
Apr 2015
63
34
What do you mean by the same concentration?

You are correct to say that the copper carbonate will precipitate first (why did you think that?)

but the key to this is to note that the question says that the sodium carbonate is added in small quantities. (the alternative would have been the sodium carbonate was in excess)

So can you say (list) in words what will happen after the copper carbonate starts to precipitate?