Chemical Forums

Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: baboom on December 06, 2009, 06:42:13 PM

Title: Why was the solution made alkaline?
Post by: baboom 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+

Title: Re: Why was the solution made alkaline?
Post by: xoto on January 02, 2010, 12:10:30 PM

has it got to do with pH?

Title: Re: Why was the solution made alkaline?
Post by: Quaff 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.