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Specialty Chemistry Forums => Citizen Chemist => Topic started by: vmelkon on April 07, 2012, 05:12:45 PM

Title: 2 salts
Post by: vmelkon on April 07, 2012, 05:12:45 PM
If you have a non-saturated solution of let's say MgCl2 and you add some solid Cu(OH)2, what would happen?
Would some of the Cu(OH)2 dissolve and the OH- binds with the Mg2+?
I imagine some kind of equilibrium would be reached where you have perhaps a little of one hydroxide and a lot of the other hydroxide based on the solubility of each compound.
Title: Re: 2 salts
Post by: Borek on April 07, 2012, 05:59:17 PM
Its all in Ksp values. pKsp for Cu(OH)2 is 18.6, pKsp for Mg(OH)2 is 10.7. You start with mostly neutral solution - so concentration of OH- is around 10-7. Ignoring shift of water autodissociation solubility of copper hydroxide is 3.6*10-7 - so pH doesn't change by much, it slightly goes up by just a few tenths of the unit. Even if it goes up to 8, that means [OH-] = 10-6, [OH-]2=10-12, so you would need 20 M Mg2+ to see any precipitation. It ain't gonna happen.
Title: Re: 2 salts
Post by: vmelkon on April 09, 2012, 08:37:15 AM
Would the pKsp mean that the shift would be towards Cu(OH)2?
So if you add a solution of CuCl2 to some solid Mg(OH)2, the Mg(OH)2 would slowly dissolve while some Cu(OH)2 forms?
Title: Re: 2 salts
Post by: Borek on April 09, 2012, 08:57:15 AM
Quote from: vmelkon on April 09, 2012, 08:37:15 AM
So if you add a solution of CuCl2 to some solid Mg(OH)2, the Mg(OH)2 would slowly dissolve while some Cu(OH)2 forms?

That's what I would expect.