Question

The black coating on Silver is due to_______?

Answer 1

The black coating on Silver :

• The chemical name of black coating is known as Silver sulfide $\left({\mathrm{Ag}}_2\mathrm{S}\right)$ which is formed due to the reaction of Silver with the atmosphere.
• The chemical phenomenon which is responsible for this is known as corrosion, in which a metal is attacked by substances around it such as moisture, acids, etc., and gets corroded.
• Due to this corrosion, the color of Silver changes to black, on its surface.
• Generally, when Silver gets exposed to air, it combines with the Hydrogen sulfide gas in the air forming a black Silver sulfide coating, which is insoluble in all solvents.
• The chemical equation for the formation of Silver sulfide can be given as:

$\underset{\left(\mathrm{Silver}\right)}{\mathrm{Ag}\left(\mathrm{s}\right)}+\underset{\left(\mathrm{Hydrogen}\mathrm{sulfide}\right)}{{\mathrm{H}}_2\mathrm{S}\left(\mathrm{g}\right)}\to \underset{\left(\mathrm{Black}\right)}{\underset{\left(\mathrm{Silver}\mathrm{sulfide}\right)}{{\mathrm{Ag}}_2\mathrm{S}\left(\mathrm{s}\right)}}+\underset{\left(\mathrm{Hydrogen}\mathrm{gas}\right)}{{\mathrm{H}}_2\left(\mathrm{g}\right)}$

Hence, the black coating on Silver is due to the formation of Silver sulfide $\left({\mathrm{Ag}}_2\mathrm{S}\right)$.