The black coating on silver is due to_______


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

Articles to Explore:

  1. A silver article turns black when kept in the open for a few days due to the formation of (1) H2S (2) AgS (3) AgSO4 (4) Ag2S
  2. Why there is a black coating on silver?

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1 Comment

  1. Shankar kumar bhuia

    Nice because these are nice to teaching of class of stduy

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