Question

Q.6 Silver Articles develops black coating & copper articles develops green coating. Which chemical phenomenon is involved in this change ? Give the chemical name & composition of the compounds formed in each case.

Answer 1

Answer:

corrosion

Explanation:

The phenomenon responsible for the changes seen is CORROSION. Corrosion is the deterioration of metals as a result of chemical reactions between the metal and its environment!

1. Black coating on silver coins - 

2Ag + H2S ---> Ag2S + H2

The black coating is of Ag2S or silver sulphide.

2. Green coating on copper coins -

2Cu + H2O + CO2 + O2 ---> CuCO3 . Cu(OH)2

The green coating is the result of mixture of CuCO3 or copper carbonate and Cu(OH)2 or copper hydroxide in ratio 1:1 

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Answer 2

Answer:

silver sulphide

Blacking coating on silver is due to the formation of silver sulphide (Ag2S).

and Corrosion is chemical compound