Question

What type of reaction is involved in the usage of AgBr in photography? The positive print developed is dipped in ${\mathrm{AuCl}}_3$solution at the end to impart beautiful appearance to the photograph. Explain the reaction involved in this. Justify.

Answer 1

• In photography, $\mathrm{AgBr}$(Silver bromide) is exposed to form the image and depends on the frequency of the light which is involved.
• It is a photochemical reaction of light on silver bromide to form silver metal and bromine vapors and the yellow color of silver bromide changes to greyish. This is a type of decomposition reaction.

$$\begin{gathered} 2\mathrm{AgBr}\left(\mathrm{s}\right)\to 2\mathrm{Ag}\left(\mathrm{s}\right)+{\mathrm{Br}}_2\left(\mathrm{g}\right) \\ (\mathrm{silver}(\mathrm{silver})(\mathrm{bromine}\left) \\ \mathrm{bromide}\right) \end{gathered}$$

• To enhance the appearance of photograph this print is dipped in the ${\mathrm{AuCl}}_3$ solution by giving a purple shade to the photograph. The silver particles are replaced by gold.

$$\begin{gathered} {\mathrm{AuCl}}_3\left(\mathrm{aq}\right)+3\mathrm{Ag}\left(\mathrm{s}\right)\to 3\mathrm{AgCl}\left(\mathrm{aq}\right)+\mathrm{Au}\left(\mathrm{s}\right) \\ (\mathrm{gold}(\mathrm{silver})(\mathrm{silver}\left(\mathrm{gold}\right) \\ \mathrm{trichloride})\mathrm{chloride}) \end{gathered}$$