Aqua Regia

Aqua Regia

Aqua regia (Latin for "royal water") is a highly corrosive mixture of acids, typically composed of one part concentrated nitric acid and three parts concentrated hydrochloric acid. It is renowned for its ability to dissolve noble metals such as gold and platinum, which are resistant to other acids.

Properties

Aqua regia is a fuming, yellow-orange solution that is highly reactive and unstable. The mixture is known for its vigorous reaction with metals, producing a variety of products depending on the metal involved. The solution is highly corrosive and can cause severe burns upon contact with skin.

The reactivity of aqua regia is due to the formation of nitrosyl chloride (NOCl) and chlorine (Cl₂) in solution, which are powerful oxidizing agents. The overall reaction can be represented as:

\[ \text{3 HCl} + \text{HNO}_3 \rightarrow \text{Cl}_2 + \text{NOCl} + \text{2 H}_2\text{O} \]

Uses

Aqua regia is primarily used in the laboratory for the dissolution of metals and the purification of gold. It is also used in the production of chloroauric acid, the electrolyte in the Wohlwill process for refining gold.

In analytical chemistry, aqua regia is used to prepare samples for analysis by dissolving metal samples into a solution that can be analyzed by techniques such as inductively coupled plasma mass spectrometry (ICP-MS).

Safety Precautions

Due to its highly corrosive nature, aqua regia must be handled with extreme care. Appropriate personal protective equipment (PPE) such as gloves, goggles, and lab coats should be worn. It should be prepared in a well-ventilated area, preferably in a fume hood, to avoid inhalation of harmful fumes.

Historical Context

The name "aqua regia" originates from its ability to dissolve "royal" metals like gold and platinum. It was first described by the alchemist Jabir ibn Hayyan in the 8th century. During World War II, aqua regia was famously used by Hungarian chemist George de Hevesy to dissolve the Nobel Prize medals of Max von Laue and James Franck to prevent them from being confiscated by the Nazis.

Also see

• Nitric acid
• Hydrochloric acid
• Gold
• Platinum
• Corrosive substance