Regenerating silver from tarnished silverware

Most metals tarnish in the air because of the air's oxygen, carbon dioxide, or water content. In the case of iron this forms a mixture of oxides and hydroxides. In the case of copper it forms a bit more complex mixture composed mostly of basic copper carbonate compounds and also copper chloride when near enough to the ocean. However, in the case of silver the tarnish is quite different. Silver is not attacked by either of these three chemicals, it is attacked by a very small hydrogen sulfide content from the air. This forms a black coating of silver sulfide on the surface of the metal. This is usually sanded off using an abrasive polish. This tarnish can also be regenerated back into silver using common kitchen chemicals.

3 Ag2S + 2 Al + ---> Al2S3 + 6 Ag

Al2S3 + 6 H2O ---> 2 Al(OH)3 + 3

H2S + 2 NaHCO3 ---> Na2S + 2 H2O + 2 CO2

Warnings:

This experiment may release hydrogen sulfide gas, which is toxic (smells like rotting eggs). This can also deaden the sense of smell after a few wiffs, hiding its presence. Do this experiment outside or in a fume hood.

Materials:

Aluminum foil

Sodium bicarbonate (Baking soda)

Tarnished silver (I used the lid of a sterling silver salt/pepper shaker)

August 6, 2006

60 mL distilled water, 0.95g aluminum foil and 11g sodium barcarbonate were put into a beaker with the piece of tarnished silver. The aluminum was carefuly put in electrical contact with the silver to ensure proper transfer of electrons.

This was heated on a hotplate. The solution bubbled and foamed. A greyish precipitate appeared in the solution. This was continued for about half an hour until the bubbling slowed, then the silver was rinsed, the chemicals replaced, and the heating resumed. This was repeated several times.

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