Question

Rahul has been collecting copper coins and silver coins one day he observed a green coating on copper coins and black coating on Silver coins state the chemical phenomenon responsible for this coatings and also write chemical names of each coating.

Answer 1

Both the cases are of corrosion.
I. 4Cu + O2 ---> 2Cu​2O
 Due to formation of copper oxide, there is a green coating on copper coins.

II. 2Ag + 2H2S ---> Ag2S + 2H2
 Due to formation of silver sulphide, there is a black coating on silver coins.
 

Answer 2

Hey mate..
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The answer to your question is:--
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One day , Rahul observed a green coating on copper because his copper reacted with moist Carbon Dioxide ( CO2 ) in the air and it slowly lost its shiny brown surface and gained a green coat. That green substance so formed was of Copper Carbonate ( CuCO3.Cu[OH]2 ).

The chemical equation for the above reaction is:--

2Cu + O2 + H2O + CO2 → Cu(OH)2.CuCO3

Rahul also observed black coating on Silver for the fact that Silver reacted with sulphur in the air and formed a black coating of Silver Sulphide ( AgS ).

The chemical equation for the above reaction is-->

Ag (s) + S (g) ---> AgS (s)

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LOL