Polished and tarnished silver spoons

Polished and tarnished silver spoons

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Credit: SCIENCE PHOTO LIBRARY

Caption: Silver tarnish. A pair of spoons, one recently polished and the other with a dark tarnish. The tarnish is a layer of silver sulphide, formed by a reaction with oxygen and trace amounts of hydrogen sulphide in the air. The reaction is describe by the equation 4Ag + O2 + 2H2S = 2Ag2S + 2H2O. Once a thin layer of tarnish forms it blocks further hydrogen sulphide reaching the silver below, thus tarnish is a self-limiting process. Tarnish can be removed electrochemically, but is normally removed by polishing with a very fine abrasive.

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Keywords: clean, cleaned, coated, coating, comparison, corroded, corrosion, cutlery, dark, decoration, decorative, domestic, dull, everyday, familiar, grand, grandeur, home, hydrogen sulphide, oxidation, pair, polish, polished, polishing, school science, science education, shiny, silver, silver sulphide, spoon, spoons, tarnish, tarnished, tarnishing, utensil

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