The Black Coating On Silver is Due To?

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

Following is the equation for the formation of silver sulphide:

\(2Ag\;(s)+H_{2}S\;(g)\rightarrow Ag_{2}S\;(s)+H_{2}\;(g)\)

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

Chemical formula Ag2S
Molecular weight 247.8
Crystal structure Orthogonal
Group Silver: 11 and Sulfur: 16

Mechanical and Thermal Properties of Silver Sulphide

Density 7.23g/cm3
Melting point 825dC
Heat of fusion 56.9J/g
Heat of formation -32.6kJ/mol

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