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A student has been collecting silver coi...

A student has been collecting silver coins and copper coins. One day she observed a black coating on silver coins and a green coating on copper coins. Which chemical phenomenon is responsible for these coatings ? Write the chemical names of black and green coatings ?

Text Solution

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The phenomenon is called corrosion. The black coating is silver sulphide (`Ag_2S`) formed due to the reaction of `H_2S` gas present in the atmosphere with silver and the green coating is basic copper carbonate formed due to the reaction of moist air (`CO_2, O_2` and `H_2O` vapours) with copper.
`underset("Silver")(2Ag)+underset("Hydrogen sulphide")(H_2S) rarr underset("(Black)")underset("Silver sulphide")(Ag_2S)+ underset("Hydrogen")(H_2)`
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