Question

One day Reeta went to a jeweler’s shop with her mother. Her mother gave old gold jewelry to the goldsmith to polish. The next day when they brought the jewelry back, they found that there was a slight loss in its weight. Can you suggest a reason for the loss of weight?

Answer 1

Gold polishing aqua regia

• Gold ornaments are polished in a solution mixture of Nitric acid and Hydrochloric acid(aqua regia) in $1:3$ ratio respectively.
• The outer layer of the gold dissolves in the acidic solution and the inner shiny layer will be visible.
• Due to this loss of the upper layer of jewelry, the weight of ornaments will get reduced.
• Nitric acid is a powerful oxidizer, which will actually dissolve a small amount of gold by forming gold ions ($\mathrm{A}{\mathrm{u}}^{3+}$).
• Hydrochloric acid provides a ready supply of chloride ions ($\mathrm{C}{\mathrm{l}}^{-}$), reaction with Hydrochloric acid$\left(\mathrm{HCl}\right)$ is an equilibrium reaction that favors the formation of Chloroauric anions ($\mathrm{AuC}{{\mathrm{l}}_4}^{-}$ ).

Therefore, the loss of weight is due to the reaction of gold with the aqua regia.