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Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: Donaldson Tan on July 27, 2004, 11:41:20 PM

Title: Solubility of Silver Chromate(VI)
Post by: Donaldson Tan on July 27, 2004, 11:41:20 PM

Standard QA of Silver Chromate(VI) yields the following the result:

Yellow Precipitate formed upon addition of aq Silver Nitrate, soluble in Nitric Acid and Aq. NH3. I'm not sure why Ag2CrO4 formed dissolves in both HNO3 and NH3.

(1)- 2[CrO4]2- + 2H+ <-> [Cr2O7]2- + H2O
(2)- Ag2CrO4 (s) <-> 2Ag+ (aq) + CrO4^2- (aq)
I think addition of dil. HNO3 favours the forward the reaction of eqbm (1), thus reducing the availability of chromate(VI) ions in the solution, hence more silver chromate(VI) will dissolve, in accordance to Le Chaterlier's Principle acting in Eqbm(2).

In the case of solubility in ammonia, I think it's because of NH3's ability to form diamine silver complex.

Can someone enlighten me?

Title: Re:Solubility of Silver Chromate(VI)
Post by: Mitch on July 30, 2004, 02:13:53 AM

I think you nailed the solubility aspect. I'm not quite sure why dilute acid oxidizes Chromium better, but your logic makes sense. I'll look into some Chromium chemistry and see if I can have a better answer for you tomorrow.

Title: Re:Solubility of Silver Chromate(VI)
Post by: AWK on July 30, 2004, 03:30:15 AM

First of all - silver chromate is not yellow - it is red-brown. Of course it is soluble in both: HNO₃ and NH₃, yes, beacuse of forming dichromate anion, and diammine complex, respectively.

Title: Re:Solubility of Silver Chromate(VI)
Post by: Donaldson Tan on August 27, 2004, 05:07:44 AM

thank you so much..

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