Aqua rezia

                                           Aqua rezia

Formula: HNO₃+3HCL

Boiling point: 108 °C

Melting point: -42 °C

Density: 1.21 g/cm³

NFPA 704 (fire diamond): 0 3 0OX

Solubility in water: Miscible

Appearance: Red, yellow or gold fuming liquid

INVENTED BY: Jabir Bin Hayyan

Aqua Regia Definition

Aqua regia is a mixture of hydrochloric acid (HCl) and nitric acid (HNO₃) at a ratio of either 3:1 or 4:1. It is a reddish-orange or yellowish-orange fuming liquid. The term is a Latin phrase, meaning "king's water". The name reflects the ability of aqua regia to dissolve the noble metals gold, platinum, and palladium. Note aqua regia will not dissolve all noble metals. For example, iridium and tantalum are not dissolved.

Also Known As: Aqua regia is also known as royal water, or nitro-muriatic acid (1789 name by Antoine Lavoisier)

Aqua Regia History

Some records indicate a Muslim alchemist discovered aqua regia around 800 AD by mixing a salt with vitriol (sulfuric acid). Alchemists in the Middle Ages tried to use aqua regia to find the philospher's stone. The process to make the acid was not described in chemistry literature until 1890.

The most interesting story about aqua regia is about an event that occurred during World War II. When Germany invaded Denmark, the chemist George de Hevesy dissolved the Nobel Prize medals belonging to Max von Laue and James Franck into aqua regia. He did this to prevent the Nazis from taking the medals, which were made of gold. He put the solution of aqua regia and gold on the shelf in his lab at the Niels Bohr Institute, where it looked like just another jar of chemicals. de Hevesy returned to his laboratory when the war was over and reclaimed the jar. The recovered the gold and gave it to the Royal Swedish Academy of Sciences so the Nobel Foundation to re-make the Nobel prize medals to give to Laue and Franck.

Storage

Do not store aqua regia.  Aqua regia quickly loses it effectiveness due to oxidation of its reactive components. Mix a fresh solution for each use.  Excess solutions should be neutralized with sodium bicarbonate and disposed via the drain, followed by flushing with copious amounts of water.

Disposal

After the material has cooled, the spent solution should be neutralized with sodium bicarbonate and disposed via the drain, followed by flushing with copious amounts of water. If the solution is contaminated with heavy metals (i.e. silver, chromium), the neutralized solution should be collected as hazardous waste.

Wohlwill process for refining gold. Although gold is typically an inert metal, it will dissolve in aqua regia due to the unique action of nitric and hydrochloric acid. Nitric acid is a powerful oxidising agent, capable of converting small amounts of gold to its ionic form, Au³⁺. Once this ionic form is present in the solution, the hydrochloric acid provides a source of chlorine anions which react with the gold cations to form tetrachloroaurate(III) anions. As the reaction with hydrochloric acid is an equilibrium reaction favouring the formation of chloroaurate anions (AuCl₄^-), the gold ions are removed from solution making room for more oxidation to occur. And as the solution is so acidic, the chloroaurate anions are swiftly protonated to form chloroauric acid. Using this method, it is possible to produce gold with a jaw-dropping purity of 99.999%. Due to its reactivity and strength, aqua regia it can also dissolve platinum  in a similar way.

Another common use for aqua regia is the deep cleaning the tubes used in nuclear magnetic resonance, or NMR, spectroscopy. It is very efficient at this as it is able to remove all traces of the paramagnetic element chromium, which can contaminate spectra and ruin research.