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Topic: question about solubility  (Read 3178 times)

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Offline stelzyr

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question about solubility
« on: February 16, 2009, 03:07:02 AM »
I've read that zinc oxide is insoluble in water, but from certain journal papers I gathered that the solubility of ZnO in water with pH 8.0 and at 25 deg C is ~1.5 mg/L. I've two questions about situations below the given saturation value:

1) Does that mean if I dissolve 1.4 mg of ZnO in 1 L water at the stated conditions, it'll dissolve completely to give 1.12 mg Zn2+/L? Or will only a certain proportion, like say 16%, of the salt dissolve and so I'll only get 0.18 mg Zn2+/L?
2) If the answer is yes to the later question, will the amount of solid salt that I add to water affect the amount dissolved? E.g. If I add 0.2 mg of ZnO and 1 mg of ZnO to water, will the proportion dissolved remain the same?

Thanks and I'd appreciate it very much if the answers can come with references, or anyone can direct me to reliable sources (chemistry textbooks, journals etc.) that can help me answer these questions.

Offline AWK

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Re: question about solubility
« Reply #1 on: February 16, 2009, 07:14:34 AM »
Dissolution of ZnO in alkaline water is caused by a reaction:
ZnO + H2O + OH- = [Zn(OH)3-]
in diluted solution of hydroxide
ZnO + H2O + 2OH- = [Zn(OH)42-]
in  more concentrated hydroxide.
This is an equilibrium reaction, and in equilibrium concentration of hydroxozinkate in solution depends only on temperature and concentration of hydroxide anion assuming an excess of ZnO is present. Of course, system should have enough time to equilibrate. 

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