Gold metal will not dissolve in either concentrated nitric...

Gold metal will not dissolve in either concentrated nitric acid on concentrated hydrochloric acid. It will dissolve, however, in aqua regia, a mixture of the two concentrated acids. The products of the reaction are the $\mathrm{AuCl}_{4}^{-}$ ion and gaseous NO. Write a balanced equation for the dissolution of gold in aqua regia.

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Key Concepts

Aqua Regia

Aqua regia is a highly reactive mixture of concentrated nitric acid and hydrochloric acid. Its unique ability to dissolve noble metals, such as gold, arises from the combined oxidative power of nitric acid and the complexing ability of chloride ions from hydrochloric acid.

Redox Reactions

Redox reactions are chemical processes involving the transfer of electrons between species. In the context of dissolving gold with aqua regia, gold is oxidized from its elemental state to form gold ions while nitric acid is reduced, often producing nitrogen oxides as by-products.

Complex Ion Formation

Complex ion formation involves the bonding of metal ions with surrounding ligands, such as chloride ions, to produce stable complex species. When gold is oxidized, the resulting gold ions form a stable complex with multiple chloride ions (e.g., AuCl4-) which helps stabilize and dissolve the metal in solution.

Balancing Chemical Equations

Balancing chemical equations is a fundamental concept in stoichiometry, ensuring that mass and charge are conserved in a chemical reaction. This concept is essential when writing the dissolution reaction of gold in aqua regia to accurately reflect the reactants and products involved.

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