I am trying to experiment with changing the pH of silver nitrate and ascorbic acid to basic pH using sodium hydroxide to get Ag metal. The solution turns black after adding the sodium hydroxide leading me to believe that somehow silver hydroxide is forming and not silver metal. Why is this happening? How can I avoid using ammonia to change pH since I do not have adequate fume hood and so the smell will be dangerous. Plus, I do not want to form a complex with silver ion with the ammonia.
Dear Dan Colomb, in order to obtain a nice Ag mirror, you cannot avoid working with ammonia solution. Addition of sodium hydroxide to silver nitrate solution yields dark, unstable AgOH which finally converts to dark Ag2O which is more stable. For making Tollens' reagent it is essential that you form the soluble silver diammine complex [Ag(NH3)2]+. This can be done by dissolving preformed Ag2O im ammonia solution, or by using ammonia solution and AgNO3 right away, Thus you should perhaps ask a colleague who has a fume hood available.
Dan Colomb A perfect answer from Frank T. Edelmann You can‘t avoid the chemistry... I’d only add that the redox potentials to the metal for the diammine complex and nitrate are very different. Note that, in air, the surface of ‘silver’ particles is in the +1 oxidation state i.e. not metal...
Dan Colomb Forgot to add this webinar:
Silver colloids and invisible ink
https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W150902SilverColloidInvisibleInk.html
Tollens' reagent is on slide 26 and the redox potentials on slide 27.
Look at the Pourbaix diagram for silver in solution. There is one on:
http://www.ijscer.com/uploadfile/2017/0907/20170907022523204.pdf
This tells you exactly what system is stable at which pH. Another Pourbaix diagram involving ammonia is in:
Article Dissolution behavior of silver in ammoniacal solutions using...
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