Answer:
Blacking coating on silver is due to the formation of silver sulphide (Ag2S).
When silver is exposed to air, it combines with the hydrogen sulphide gas in the air to generate a black silver sulphide coating. In all solvents, silver sulphide is insoluble.
The Following is the equation for the formation of silver sulphide:
\(\begin{array}{l}2Ag\;(s)+H_{2}S\;(g)\rightarrow Ag_{2}S\;(s)+H_{2}\;(g)\end{array} \) |
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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