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Topic: Solubility Product Question  (Read 9114 times)

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Offline darkprince304

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Solubility Product Question
« on: March 21, 2012, 01:26:27 AM »
Hi Im new here

Why is Mg(OH)2 sparingly soluble in water but highly soluble in ammonium
chloride solution.
Can I know the reason?

Thanks :)

Offline UG

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Re: Solubility Product Question
« Reply #1 on: March 21, 2012, 02:01:11 AM »
Because NH4+ is an acid and Mg(OH)2 is a base, the two can react. Does that answer your question?

Offline darkprince304

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Re: Solubility Product Question
« Reply #2 on: March 21, 2012, 02:07:58 AM »
Um, thanks but I still don't get it. If they both can react how is it soluble in NH4Cl and what is the relation of solubility product with it?

Offline UG

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Re: Solubility Product Question
« Reply #3 on: March 21, 2012, 02:13:35 AM »
If they both can react how is it soluble in NH4Cl and what is the relation of solubility product with it?
You can think of the dissolution as an equilibrium Mg(OH)2 (s)  ::equil:: Mg2+ + 2OH-
Now if the hydroxide ions react with the NH4+ what will happen to the equilibrium?

Offline darkprince304

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Re: Solubility Product Question
« Reply #4 on: March 21, 2012, 02:19:36 AM »
It will go backward?

Offline UG

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Re: Solubility Product Question
« Reply #5 on: March 21, 2012, 02:27:04 AM »
It will go backward?
Eh, not quite. The reaction with NH4+ reduces the amount of OH- ions, ie, they are 'consumed' from the equilibrium with magnesium hydroxide solid. So essentially, you are removing OH- ions from the expression Mg(OH)2 (s)  ::equil:: Mg2+ + 2OH-, this will cause the solid to dissolve more in order to produce more OH- ions to react with NH4+. The result of this is that the solid has become more soluble in the NH4Cl solution.

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