Aqua Regia Dissolving Gold
Au + 3HCl + HNO3 → HAuCl4 + NO + 2H2O
Overview
Aqua regia (3:1 mixture of HCl and HNO₃) dissolves gold, which is inert to either acid alone. Nitric acid oxidizes gold to Au³⁺ while hydrochloric acid provides chloride ions that stabilize the gold as [AuCl₄]⁻ complex. The synergy between the two acids makes aqua regia effective against noble metals.
Participants
| Role | Substance | Coefficient | State |
|---|---|---|---|
| Reactant | Gold Au | 1 | (s) |
| Reactant | Nitric Acid HNO₃ | 1 | (aq) |
| Reactant | Hydrochloric Acid HCl | 3 | (aq) |
| Product | Water H₂O | 2 | (l) |
Everyday Example
During WWII, George de Hevesy dissolved the Nobel Prize gold medals of Max von Laue and James Franck in aqua regia to hide them from the Nazis.
Industrial Importance
Aqua regia is used in gold refining, analytical chemistry for dissolving noble metals, and in recovering precious metals from electronic waste.
Properties
- Type
- Redox
- Reversible
- No
- Energy
- Exothermic
- ΔH
- -150.0 kJ/mol
Related Reactions
Bleaching with Sodium Hypochlorite
Cerium(IV) Reduction by Iron(II)
Chlorine Oxidation of Bromide
Chromate-Dichromate Equilibrium
Contact Process SO₂ Oxidation
Copper Displaced by Iron
Copper Oxidation by Nitric Acid
Copper Patina Formation (Verdigris)
Copper Reduction of Silver Ion
Dichromate Oxidation of Ethanol
Frequently Asked Questions
What is the equation for Aqua Regia Dissolving Gold?
The balanced equation is: Au + 3HCl + HNO₃ → HAuCl₄ + NO + 2H₂O.
What type of reaction is Aqua Regia Dissolving Gold?
Aqua Regia Dissolving Gold is a redox reaction.
Is Aqua Regia Dissolving Gold exothermic or endothermic?
Aqua Regia Dissolving Gold is exothermic (releases energy). The enthalpy change (ΔH) is -150.0 kJ/mol.