Precipitating Silver

Name: Manuel
Status: other
Grade: other
Location: IL

Question: I am an editor of science and math textbooks, and I am writing a
sort of "natural history of chemistry" book with illustrations. I need help
with one experiment that I would like to photograph. It is easy to force Ag
to precipitate out of an AgNO3 solution using Cu or some other metals, but
is there a simple way to do it without dissolving any metal? I am
photographing some of these reactions for my book and I do not want my
readers to get the impression that the metal used to induce the
precipitation is somehow being transmuted into silver. I am not trying to
illustrate the specific properties of silver but its indestructibility, and
I think it would be pedagogically distracting to have a sacrificial chunk
of metal. The ideal reaction would cause most or all of the silver to
precipitate, ideally as needles or grains as opposed to powder. It does not
matter if the reaction is slow (even weeks), because the idea is to
photograph the recovery of the silver, not to do a live demo. I do have
access to many common acids, bases, salts and other reagents.
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The website:

http://www.chemistryquestion.com/English/Questions/HighSchoolChemistry/6_silvermirrorreaction_reducingpower.html

gives a fairly thorough discussion of methods of reducing silver ion to
silver metal. Here the "active" reagent is formaldehyde. In addition there
is the "classic" reduction of Ag(+1) using sodium thiosulfate -- the
chemical reaction used in traditional photography. This reaction would have
the dual purpose of showing the reduction of silver ion to silver metal and
also connects it with the chemistry of traditional photography. I do not know
if you will get a "silver mirror" with any of these approaches. The particle
size is small the silver may just look black. You can also produce a silver
mirror using Tollen's reagent: See:

http://www.uni-regensburg.de/Fakultaeten/nat_Fak_IV/Organische_Chemie/Didaktik/Keusch/D-Tollens-e.htm

which is used to identify aldehydes
If my memory is correct, this produces a very nice mirror effect.

Vince Calder
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