Aqua regia 62929 224932514 2008-07-11T01:50:54Z 68.13.243.82 /* Dissolving platinum */ [[Image:Aqua regia in NMR tubes.jpg|right|thumb|Freshly prepared aqua regia is colorless, but it turns orange within seconds. Here, fresh aqua regia has been added to these [[NMR tube]]s to remove all traces of organic material.]] '''Aqua regia''' ([[Latin]] for '''royal water''') is a highly corrosive, fuming yellow or red solution. The [[mixture]] is formed by freshly mixing concentrated [[nitric acid]] and concentrated [[hydrochloric acid]], usually in a volumetric ratio of 1:3 respectively. It is one of the few [[reagent]]s that dissolves [[gold]] and [[platinum]]. It was so named because it can dissolve the so-called royal, or [[noble metal]]s, although [[tantalum]], [[iridium]], and a few other metals are able to withstand it. ==Applications== Aqua regia is used in [[chemical etching|etching]] and in certain [[Analytical chemistry|analytic procedures]]. It is also used in some laboratories to clean [[laboratory glassware|glassware]] of [[organic compound]]s and metal particles. [[Image:John J Aqua Regia.JPG|right|thumb|Freshly prepared aqua regia to remove metal salt deposits.]] This method is preferred over the "traditional" [[chromic acid]] bath for cleaning [[NMR tube]]s, because no traces of paramagnetic [[chromium]] can remain to later ruin acquired spectra.<ref>Hoffman, R., [http://chem.ch.huji.ac.il/nmr/preparation/preparation.html How to make an NMR sample], [[Hebrew University]], 10 Mar 2005. Accessed 31 Oct 2006.</ref> (Relatedly, chromic acid baths are further discouraged because of the high toxicity of chromium and the potential for explosions). Aqua regia is itself very corrosive and has been implicated in several explosions as well due to mishandling and it should not be used unless gentler cleaning techniques such as the use of brushes, [[sonication]], detergents, or milder oxidisers are inadequate.<ref>[[American Industrial Hygiene Association]], [http://www2.umdnj.edu/eohssweb/aiha/accidents/explosion.htm Laboratory Incidents: Explosions], 8 Dec 2004. Accessed 31 Oct 2006.</ref> Due to the reaction between its components resulting in its [[#Decomposition of aqua regia|decomposition]], aqua regia quickly loses its effectiveness. As such, its components should only be mixed immediately before use. While local regulations may vary, aqua regia may be disposed of by carefully neutralizing with an appropriate agent—such as [[sodium bicarbonate]]—before pouring down the sink. If there is a large amount of metal in solution with the acid, it may be preferable to carefully neutralize it, and absorb the solution with a solid material such as [[vermiculite]] before discarding it with solid waste. This practice should not be used when EPA regulated or otherwise [[Heavy metals|toxic metals]] are present. ==Chemistry== ===Dissolving gold=== Aqua regia dissolves gold, even though neither constituent acid will 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 (Au<sup>3+</sup>). The hydrochloric acid provides a ready supply of chloride ions (Cl<sup>-</sup>), which react with the gold to produce chloraurate anions, also in solution. The reaction with hydrochloric acid is an equilibrium reaction which favors formation of chloraurate anions (AuCl<sub>4</sub><sup>-</sup>). This results in a removal of gold ions from solution and allows further oxidation of gold to take place, and so the gold is dissolved. In addition, gold may be oxidized by the free chlorine present in aqua regia. Appropriate [[chemical equations|equations]] are :Au ''(s)'' + 3 NO<sub>3</sub><sup>-</sup> ''(aq)'' + 6 H<sup>+</sup> ''(aq)'' → Au<sup>3+</sup> ''(aq)'' + 3 NO<sub>2</sub> ''(g)'' + 3 H<sub>2</sub>O ''(l)'' and :Au<sup>3+</sup> ''(aq)'' + 4 Cl<sup>-</sup> ''(aq)'' → AuCl<sub>4</sub><sup>-</sup> ''(aq)''. The oxidation reaction can also be written with [[nitric oxide]] as the product rather than [[nitrogen dioxide]]: :Au ''(s)'' + NO<sub>3</sub><sup>-</sup> ''(aq)'' + 4 H<sup>+</sup> ''(aq)'' → Au<sup>3+</sup> ''(aq)'' + NO ''(g)'' + 2 H<sub>2</sub>O ''(l)''. ===Dissolving platinum=== Similar equations can be written for platinum. As with gold, the oxidation reaction can be written with either nitric oxide or nitrogen dioxide as the nitrogen oxide product. :Pt ''(s)'' + 4 NO <sub>3</sub><sup>-</sup> ''(aq)'' + 8 H<sup>+</sup> ''(aq)'' → Pt<sup>4+</sup> ''(aq)'' + 4 NO<sub>2</sub> ''(g)'' + 4 H<sub>2</sub>O ''(l)'' :3Pt ''(s)'' + 4 NO <sub>3</sub><sup>-</sup> ''(aq)'' + 16 H<sup>+</sup> ''(aq)'' → 3Pt<sup>4+</sup> ''(aq)'' + 4 NO ''(g)'' + 8 H<sub>2</sub>O ''(l)'' The oxidized platinum ion then reacts with chloride ions resulting in the chloroplatinate ion. :Pt<sup>4+</sup> ''(aq)'' + 6 Cl<sup>-</sup> ''(aq)'' → PtCl<sub>6</sub><sup>2-</sup> ''(aq)'' Experimental evidence reveals that the reaction of platinum with aqua regia is considerably more complex. The initial reactions produce a mixture of chloroplatinous acid (H<sub>2</sub>PtCl<sub>4</sub>) and nitrosoplatinic chloride ((NO)<sub>2</sub>PtCl<sub>4</sub>). The nitrosoplatinic chloride is a solid product. If full dissolution of the platinum is desired, repeated extractions of the residual solids with concentrated hydrochloric acid must be performed. :Pt ''(s)'' + 2 HNO<sub>3</sub> ''(aq)'' + 4 HCl ''(aq)'' → (NO)<sub>2</sub>PtCl<sub>4</sub> ''(s)'' + 3 H<sub>2</sub>O ''(l)'' + 1/2 O<sub>2</sub> ''(g)'' :(NO)<sub>2</sub>PtCl<sub>4</sub> ''(s)'' + 2 HCl ''(aq)'' → H<sub>2</sub>PtCl<sub>4</sub> ''(aq)'' + 2 NOCl ''(g)'' The chloroplatinous acid can be oxidized to [[chloroplatinic acid]] by saturating the solution with chlorine while heating. :H<sub>2</sub>PtCl<sub>4</sub> ''(aq)'' + Cl<sub>2</sub> ''(g)'' → H<sub>2</sub>PtCl<sub>6</sub> ''(aq)'' === Decomposition of aqua regia === Upon mixing of concentrated hydrochloric acid and concentrated nitric acid, chemical reactions occur. These reactions result in the volatile products [[nitrosyl chloride]] and [[chlorine]] as evidenced by the fuming nature and characteristic yellow color of aqua regia. As the volatile products escape from solution, the aqua regia loses its potency. :HNO<sub>3</sub> ''(aq)'' + 3 HCl ''(aq)'' → NOCl ''(g)'' + Cl<sub>2</sub> ''(g)'' + 2 H<sub>2</sub>O ''(l)'' Nitrosyl chloride can further decompose into [[nitric oxide]] and chlorine. This dissociation is equilibrium-limited. Therefore, in addition to nitrosyl chloride and chlorine, the fumes over aqua regia contain nitric oxide. :2 NOCl ''(g)'' → 2 NO ''(g)'' + Cl<sub>2</sub> ''(g)'' == History == [[Image:Jabir ibn Hayyan.jpg|thumb|200px|right|[[Geber|Jabir ibn Hayyan]], medieval manuscript drawing, anonymous]] Hydrochloric acid was first discovered around the year [[800]] by the [[Alchemy and chemistry in Islam|Arab alchemist]], [[Geber|Abu Musa Jabir ibn Hayyan]] (Geber), by mixing [[sodium chloride|common salt]] with [[vitriol]] ([[sulfuric acid]]). Jabir's invention of gold-dissolving aqua regia, consisting of hydrochloric acid and [[nitric acid]], contributed to the effort of alchemists to find the [[philosopher's stone]].<ref name=Hassan>{{cite web |url= http://www.history-science-technology.com/Articles/articles%2072.htm |title=Technology Transfer in the Chemical Industries |accessdate=2008-03-29 |last=Hassan |first=Ahmad Y |authorlink=Ahmad Y Hassan |work=History of Science and Technology in Islam }}</ref> When [[Germany]] invaded [[Denmark]] in [[World War II]], the Hungarian chemist [[George de Hevesy]] dissolved the gold [[Nobel Prize]]s of [[Max von Laue]] and [[James Franck]] into aqua regia to prevent the Nazis from stealing them. He placed the resulting solution on a shelf in his laboratory at the [[Niels Bohr Institute]]. It was subsequently ignored by the Nazis who thought the jar—one of perhaps hundreds on the shelving—contained common chemicals. After the war, de Hevesy returned to find the solution undisturbed and precipitated the gold out of the acid. The gold was returned to the Royal Swedish Academy of Sciences and the Nobel Foundation presented new medals to Laue and Franck.<ref>{{cite web | publisher = The Nobel Foundation | url = http://nobelprize.org/nobel_prizes/medals/ | author = Birgitta Lemmel | title = The Nobel Prize Medals and the Medal for the Prize in Economics | date = 2006}}</ref> ==In art and entertainment== ===Literature=== * ''[[Cryptonomicon]]'', by [[Neal Stephenson]] - The fuel for the "Galvanick Lucipher" (a sort of specialized lantern) used by the butler Ghnxh on Qwghlm. Oddly, the mechanical fixings for the electric parts immersed in the aqua regia are described as being made of "hammered gold". *''[[The Crying of Lot 49]]'' by [[Thomas Pynchon]] - During ''The Courier's Tragedy,'' the faithful servant Ercole pours aqua regia into a steel box around the traitor Domenico's head. ==See also== * [[Aqua fortis]] * [[Aqua vitae]] * [[Chromic acid]] * [[Digger gold]] * [[Sulfuric acid]] * [[Nitric acid]] ==References== <references/> ==External links== * [http://jchemed.chem.wisc.edu/JCESoft/CCA/CCA3/MAIN/AQREGIA/PAGE1.HTM Chemistry Comes Alive! Aqua Regia] * [http://www.bartleby.com/65/aq/aquaregi.html The Columbia Encyclopedia: Aqua Regia] [[Category:Gold]] [[Category:Acids]] [[Category:Alchemical substances]] [[bs:Aqua regia]] [[bg:Царска вода]] [[cs:Lučavka královská]] [[da:Kongevand]] [[de:Königswasser]] [[et:Kuningvesi]] [[el:Βασιλικό Ύδωρ]] [[es:Agua regia]] [[fr:Eau régale]] [[ko:왕수]] [[hr:Zlatotopka]] [[id:Aqua regia]] [[is:Kóngavatn]] [[it:Acqua regia]] [[he:מי מלך]] [[lt:Karališkasis vanduo]] [[hu:Királyvíz]] [[ml:അക്വാ റീജിയ]] [[nl:Koningswater]] [[ja:王水]] [[no:Kongevann]] [[pl:Woda królewska]] [[pt:Água régia]] [[ro:Aqua regia]] [[ru:Царская водка]] [[simple:Aqua regia]] [[sk:Lúčavka kráľovská]] [[sr:Царска вода]] [[sh:Carska voda]] [[fi:Kuningasvesi]] [[sv:Kungsvatten]] [[vi:Nước cường toan]] [[tr:Kral suyu]] [[uk:Царська вода]] [[zh:王水]] [[kn:ರಾಜೋದಕ]]