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Topic: General Chemistry Help  (Read 1620 times)

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Offline jweavss

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General Chemistry Help
« on: October 28, 2013, 04:26:13 PM »
I have a practice test that I'm using to study for my general chemistry exam. I have it all done except one problem. Can someone work through this problem, so I can check it with my work to look for my mistake? I've worked it over and over, so I must be missing something. Thanks!

A 7.16 gram sample of a soluble aluminum compound was dissolved in water. When an excess of NaOH was added to the solution, 2.31 grams of precipitate formed. What is the mass percentage of aluminum in the original compound?
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Offline DrCMS

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Re: General Chemistry Help
« Reply #1 on: October 28, 2013, 04:44:54 PM »
What do you think the precipitate could be?
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Offline AWK

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Re: General Chemistry Help
« Reply #2 on: October 29, 2013, 03:24:12 AM »
Completely wrong problem! An excess of NaOH dissolves amphoteric aluminium hydroxide easily. Use ammonia instead of NaOH. Then dissolution of aluminium hydroxide is insignificant.
Start from a balanced reaction.
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Offline DrCMS

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Re: General Chemistry Help
« Reply #3 on: October 29, 2013, 06:09:16 AM »
Sorry I'd missed the significance of the excess NaOH, so a poor question. 
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