Solubility constant

[danny89]

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Question: The addition of excess Ca to a solution containing Ca and CO3 ions causes CaCO3 to precipitate because:
Answer: Because the reactivity quotient will be greater than Ksp.
I understand that Ksp=[Ca][CO3] and that adding an excess of Ca will cause CaCO3 to precipitate more. But why does [CO3] decrease and the Ksp stays the same? Is it because it's consumed when the reaction is shifted to the left? (CaCO3<---->Ca + CO3)

 

[sazerac]

Question: The addition of excess Ca to a solution containing Ca and CO3 ions causes CaCO3 to precipitate because:
Answer: Because the reactivity quotient will be greater than Ksp.
I understand that Ksp=[Ca][CO3] and that adding an excess of Ca will cause CaCO3 to precipitate more. But why does [CO3] decrease and the Ksp stays the same? Is it because it's consumed when the reaction is shifted to the left? (CaCO3<---->Ca + CO3)

Well, the Ksp stays the same because it is a "Konstant". If Constant=AxB, and you suddenly add a lot more A, you need to run your reaction in reverse and get rid of some A and B, until the Constant is restored again. In the end you'll have less B than you started with, and more A than you started with (before you added all that extra A).

 

[danny89]

Thank you 👍