Question

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

Answer 1

HELLO DEAR,


when silver react with hydrogen sulphide in presence of air (oxygen)
to form a silver sulphide in black colour
Equation is :-

2Ag + H2S ---------- Ag2S +H2

copper metal is naked to moist air(oxygen)
due to
formation of copper carbonate ( corrosion of copper) it develops a green layer
Equation is:-
2Cu + O2 + CO2 + H2O → CuCO3.Cu(OH)2

I HOPE ITS HELP YOU DEAR,
THANKS

Answer 2

Hey Friend,

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 

Hope it helps!