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Solubility Equilibrium

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emm316:
If the ion concentration of two ions in a reaction are different how will they reach equilibrium?
like in CaSO4  ::equil:: Ca2+ + SO4 2- if the calcium ion concentration is 0.04M and the sulfate ion concentration is 0.01 M and at equilibrium the ion concentration for both is 4.99x10-3 M how would they both get to the same concentration??

Borek:

--- Quote from: emm316 on January 17, 2020, 09:03:18 PM ---at equilibrium the ion concentration for both is 4.99x10-3 M
--- End quote ---

Not necessarily.


--- Quote from: emm316 on January 17, 2020, 09:03:18 PM ---how would they both get to the same concentration??
--- End quote ---

They won't. Equilibrium doesn't mean "same concentrations". It means "no further changes in concentrations".

Yes, for reactions like dissolution of CaSO4 (or AgCl) you can expect concentrations of both ions to be the same, but that's just because of the reaction stoichiometry. What about dissolution of Ag2S? Ca3(PO4)2?

What will happen in your case is that some CaSO4 will precipitate till concentrations of whatever is left will be described by the solubility product (Ksp) of the compound.

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