What is the purpose of "Concentrated Hydrochloric Acid" in aqua regia?
What is the purpose of "Concentrated Hydrochloric Acid" in aqua regia?
Aqua regia is a mixture formed by freshly mixing concentrated nitric acid and hydrochloric acid, in a volume ratio of 1:3, respectively. It is used to dissolve noble metals like gold, platinum.
Aqua regia dissolves gold, though neither constituent acid can do so alone, because, in combination, each acid performs a different task.
Nitric acid is a powerful oxidizer, which will actually dissolve a virtually undetectable amount of gold, forming gold ions (Au3+).
Au (s) + 3 NO3− (aq) + 6 H+ (aq) → Au3+ (aq) + 3 NO2 (g) + 3 H2O (l)
The hydrochloric acid provides a ready supply of chloride ions (Cl−), which react with the gold ions to produce chloroaurate anions (AuCl4−), also in solution.
Au3+ (aq) + 4 Cl− (aq) → AuCl4− (aq)
Aqua regia is a mixture formed by freshly mixing concentrated nitric acid and hydrochloric acid, in a volume ratio of 1:3, respectively. It is used to dissolve noble metals like gold, platinum.
Aqua regia dissolves gold, though neither constituent acid can do so alone, because, in combination, each acid performs a different task.
Nitric acid is a powerful oxidizer, which will actually dissolve a virtually undetectable amount of gold, forming gold ions (Au3+).
Au (s) + 3 NO3− (aq) + 6 H+ (aq) → Au3+ (aq) + 3 NO2 (g) + 3 H2O (l)
The hydrochloric acid provides a ready supply of chloride ions (Cl−), which react with the gold ions to produce chloroaurate anions (AuCl4−), also in solution.
Au3+ (aq) + 4 Cl− (aq) → AuCl4− (aq)
