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Topic: Why was the solution made alkaline?  (Read 2512 times)

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Offline baboom

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Why was the solution made alkaline?
« on: December 06, 2009, 06:42:13 PM »
When I performed a volhard titration to find the concentration Se in a shampoo, before digestion of the sample a few drops of ammoinia was added.
Why was it made alkaline?

Here is the overall equation:

3Se+6Ag+ + 6NH3 + 3H2O---> 2Ag2Se+Ag2SeO3 +6NH4+
BABOOM!! :o

Offline xoto

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Re: Why was the solution made alkaline?
« Reply #1 on: January 02, 2010, 12:10:30 PM »
has it got to do with pH?

Offline Quaff

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Re: Why was the solution made alkaline?
« Reply #2 on: January 05, 2010, 02:17:27 PM »
it won't work in acid conditions and must be alkaline.   But use of strong base containing OH- is prohibited since it would cause the titrant to precipitate as oxide, so ammonia is used to suck up the protons liberated during the redox because the titrant ammonia adduct is soluble.

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