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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: emm316 on January 17, 2020, 09:03:18 PM

Title: Solubility Equilibrium
Post by: emm316 on January 17, 2020, 09:03:18 PM

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??

Title: Re: Solubility Equilibrium
Post by: Borek on January 18, 2020, 04:03:19 AM

Quote from: emm316 on January 17, 2020, 09:03:18 PM

at equilibrium the ion concentration for both is 4.99x10^-3 M

Not necessarily.

Quote from: emm316 on January 17, 2020, 09:03:18 PM

how would they both get to the same concentration??

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.