Question

Silver coins turn black when exposed to air. Explain using a balanced chemical equation.

Answer 1

1. Silver($\mathrm{Ag}$) coins turn black due to the formation of Silver sulphide (${\mathrm{Ag}}_2\mathrm{S}$).
2. When the Silver articles are exposed to air, they combine with the Hydrogen sulphide (${\mathrm{H}}_2\mathrm{S}$) gas in the air to form a black Silver sulphide coating.
3. Therefore, the Silver coins appear as dull or black.
4. The balanced chemical equation for the formation of Silver sulphide can be given as:

$$\begin{gathered} 2\mathrm{Ag}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{S}\left(\mathrm{g}\right)\to {\mathrm{Ag}}_2\mathrm{S}\left(\mathrm{s}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right) \\ (\mathrm{Silver}\mathrm{metal})(\mathrm{Hydrogen}\mathrm{sulphide})(\mathrm{Silver}\mathrm{sulphide})(\mathrm{Hydrogen}\mathrm{gas}) \end{gathered}$$