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Name: Valerie
Status: student
Grade: 6-8
Location: CO
Country: USA
Date: November 2007


Question:
I would like to do a test to see if flakes of metals found are gold or silver. I found in your archives a home test for gold, but I did not find a home test for silver. Do you know of any way to find out if a flake of metal is silver?



Replies:
level lab course at the University level. In recent years this has become less popular, which is unfortunate in my opinion because it not only taught lab skills, it gave the student a real "live look" at various inorganic substances. But my regret is another topic.

If you have a science teacher who can assist you, it would be desirable to obtain some nitric acid (HNO3). Silver is soluble in moderately concentrated nitric acid so some or all of metal flakes will dissolve. Separate any insoluble material from the solution by filtration, or centrifugation. If any insoluble material is dense enough you may only have to let the solid settle out under the force due to gravity. Add a few drops of hydrochloric acid to the clear solution. The formation of a white precipitate is suggestive of silver, but copper and lead have to be eliminated as possibilities, since they also form insoluble chlorides. This is done by adding a few drops of concentrated ammonia to solution/precipitate mixture.

Silver chloride is soluble in moderately concentrated ammonia, whereas copper and lead chloride are not. The finding can be re-confirmed by re-neutralizing the soluble ammonia / silver complex with excess hydrochloric acid. In which case a white precipitate will reform.

These experiments use potentially harmful substances, e.g. nitric acid, concentrated ammonia. You should seek guidance of a person knowledgeable in the handling of chemicals to assist you. Of course, wear safety glasses, use gloves, and follow good laboratory procedures. Below are some web sites where you can find further info and details.

http://www.chem.queensu.ca/PROGRAMS/UG/Firstyearlabs/112&116/
labman/manual/lab9/index.htm

http://chemlab.truman.edu/CHEM121Labs/QualAnalysis.htm

http://www.dartmouth.edu/~chemlab/chem3-5/qual_cat/full_text/
procedure.html

Vince Calder



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