Question

Silver articles become black on prolonged exposure to air. This is due to the formation of:

• A. ${\mathrm{Ag}}_3\mathrm{N}$
• B. ${\mathrm{Ag}}_3\mathrm{O}$
• C. ${\mathrm{Ag}}_2\mathrm{S}$
• D. ${\mathrm{Ag}}_2\mathrm{S}$ and ${\mathrm{Ag}}_3\mathrm{N}$

Answer 1

The correct option is C

${\mathrm{Ag}}_2\mathrm{S}$

Explanation for correct answer:-

Option (C) ${\mathrm{Ag}}_2\mathrm{S}$:

• Silver is a highly unreactive metal and thus it does not react with oxygen easily.
• But, when this Silver is exposed to the air for a very long time, it then reacts with Hydrogen sulfide gas that is present in the air.
• Thus this reaction, results in the formation of Silver sulfide which makes the silver article makes black.
• The complete reaction is:

$\underset{\mathrm{Silver}\mathrm{metal}}{2\mathrm{Ag}\left(s\right)}+\underset{\mathrm{Hydrogen}\mathrm{sulfide}}{{\mathrm{H}}_2\mathrm{S}\left(g\right)}\to \underset{\mathrm{Silver}\mathrm{sulfide}}{{\mathrm{Ag}}_2\mathrm{S}\left(\mathrm{s}\right)\left(\mathrm{black}\right)}+\underset{\mathrm{Hydrogen}}{{\mathrm{H}}_2\left(g\right)}$

Explanation for incorrect answer:-

Option (A) ${\mathrm{Ag}}_3\mathrm{N}$

• Due to the formation of Silver sulfide the silver article becomes black.
• This does not happen due to the formation of ${\mathrm{Ag}}_3\mathrm{N}$.
• Hence it is the incorrect option.

Option (B) ${\mathrm{Ag}}_3\mathrm{O}$

• ${\mathrm{Ag}}_3\mathrm{O}$ cannot exists, as silver has 1 electron in its outermost shell.
• So 2 silver atoms$\left(2{\mathrm{Ag}}^{+}\right)$ react with 1 oxygen$\left({\mathrm{O}}^{2-}\right)$ and thus form ${\mathrm{Ag}}_2\mathrm{O}$.
• Hence it is the incorrect option.

Option (D) ${\mathrm{Ag}}_2\mathrm{S}$ and ${\mathrm{Ag}}_3\mathrm{N}$

• Due to the formation of Silver sulfide only the silver article becomes black.
• This does not happen due to the formation of ${\mathrm{Ag}}_3\mathrm{N}$.
• Hence it is the correct option.

Therefore, option (C) ${\mathrm{Ag}}_2\mathrm{S}$ is the correct answer.