Blacking coating on silver is due to the formation of silver sulphide (Ag2S).
Following is the equation for the formation of silver sulphide:
What is Silver Sulphide (Ag2S)?
Silver sulphide is a dense black solid and is insoluble in all solvents but can be degraded by using strong acids. Since it is made of silver and sulfur, it has covalent bonds.
Chemical Properties of Silver Sulphide
|Group||Silver: 11 and Sulfur: 16|
Mechanical and Thermal Properties of Silver Sulphide
|Heat of fusion||56.9J/g|
|Heat of formation||-32.6kJ/mol|