Today (22 September) marks the birthday of Michael Faraday, a chemist and physicist who made significant contributions to the study of electrochemistry. He’s responsible for popularising many of the terms we use in electrochemistry today, such as anode and cathode, as well as his eponymous laws of electrolysis.
Silver tarnishes in air to form a black coating of silver sulphide, which has the formula Ag2S. The chemical equation for the formation of silver tarnish following reaction with hydrogen sulphide (H2S) is as follows:
2 Ag(s) + H2S(g) → Ag2S(s) + H2(g)
There’s speculation that, in the present day, tarnishing of silver actually occurs more quickly due to the increased amounts of hydrogen sulphide being released into the atmosphere by the combustion of fossil fuels and the like. This silver sulphide tarnish can be quite easily removed using polishes that contain abrasives to rub off the silver sulphide, but these have the disadvantage of also removing small amounts of silver. Handily, chemistry provides a method which sidesteps this problem.
