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Topic: AgCl + Na2S2O3 = . (but why does it become yellow?)  (Read 19468 times)

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Offline ade93

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AgCl + Na2S2O3 = . (but why does it become yellow?)
« on: August 15, 2012, 04:23:20 AM »
Hello!

I have dissolved silver chloride with high concentrated sodium thiosulphate where I got a silver complex called sodium dithiosulphate argentate (I) complex. The equation is found below:

AgCl + 2Na2S2O3 --> Na3[Ag(S2O3)2] (aq) + NaCl (aq)

When I had let the solution pass through a filter paper, the filter paper turned yellow as soon as it had dried. Moreover, it had increased in mass significantly. What more chemical changes has occured? Something must have decomposed, but what? ???

I would appreciate if you have any ideas!
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Offline Borek

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Re: AgCl + Na2S2O3 = . (but why does it become yellow?)
« Reply #1 on: August 15, 2012, 05:48:44 AM »
What do you know about stability of thiosulfate?
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Offline ade93

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Re: AgCl + Na2S2O3 = . (but why does it become yellow?)
« Reply #2 on: August 15, 2012, 06:19:12 AM »
Quote from: Borek on August 15, 2012, 05:48:44 AM
What do you know about stability of thiosulfate?

Thank you for the clue! :)
Since I used an excess of sodium thiosulphate, it probably might have decomposed into something (?). However, is it possible that the silver complex formed also has a tendency to decompose into a yellow substance? Or is it just the sodium thiosulphate?

I have been researching for a long time and this is the last evaluation part of my experiment essay.
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Offline Hunter2

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Re: AgCl + Na2S2O3 = . (but why does it become yellow?)
« Reply #3 on: August 15, 2012, 09:49:41 AM »
What sulfur ;D compound could be yellow?
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Offline Borek

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Re: AgCl + Na2S2O3 = . (but why does it become yellow?)
« Reply #4 on: August 17, 2012, 11:35:24 AM »
Even wikipedia page on the thiosulfate contains the answer.
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Offline ajkoer

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Re: AgCl + Na2S2O3 = . (but why does it become yellow?)
« Reply #5 on: September 17, 2012, 11:45:21 PM »
Welcome to the world of Silver Chemistry. The light yellow salt is, I strongly suspect, AgCO3, which I have also made unintentionally. Such is the affinity of CO2 (in air, water) for a soluble Silver salt.

Also note many Silver salts are light sensitive yielding grayish Ag (another surprise) and are prone to hydrolysis (yet another surprise).
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