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| {{Chembox
| | They call me Emilia. Her husband and her live in Puerto Rico but she will have to transfer 1 working day or another. What I adore performing is doing ceramics but I haven't produced a dime with it. For many years I've been working as a payroll clerk.<br><br>Feel free to surf to my homepage ... [http://www.friesboek.nl/groups/what-you-should-do-while-confronting-candida/ home std test] |
| | ImageFile = Aqua regia.svg
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| | ImageSize =
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| | Reference = <ref group="note">The information in the infobox is only accurate if the volume ratio of [[nitric acid]] to [[hydrochloric acid]] is 1:3.</ref>
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| | IUPACName = nitric acid hydrochloride
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| | OtherNames = aqua regis, nitrohydrochloric acid
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| | Section1 = {{Chembox Identifiers
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| | CASNo = 8007-56-5
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| | PubChem = 62687
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| | SMILES = [N+](=O)(O)[O-].Cl}}
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| | Section2 = {{Chembox Properties
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| | Formula = HNO<sub>3</sub>+3 HCl
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| | Appearance = red, yellow or gold fuming liquid
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| | Density = 1.01–1.21 g/cm<sup>3</sup>
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| | MeltingPt = −42 °C
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| | BoilingPt = 108 °C
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| | VaporPressure = 21 mbar
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| | Solubility = miscible in water}}
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| | Section3 = {{Chembox Hazards
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| | MainHazards =
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| | NFPA-H = 3
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| | NFPA-F = 0
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| | NFPA-R = 0
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| | NFPA-O = OX
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| | FlashPt =
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| | Autoignition = }}
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| }}
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| [[Image:Aqua regia in Davenport Laboratories.jpg|right|thumb|Freshly prepared aqua regia to remove metal salt deposits.]]
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| [[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.]]
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| '''Aqua regia''' (<small>Latin and Ancient Italian, lit.</small> "royal water"), '''''aqua regis''''' (<small>Latin, lit.</small> "king's water"), or '''nitro-hydrochloric acid''' is a highly corrosive mixture of [[acid]]s, a fuming yellow or red solution. The [[mixture]] is formed by freshly mixing concentrated [[nitric acid]] and [[hydrochloric acid]],<ref>The acid concentrations in water differ, and indicative values could be 65% w/v for nitric acid and 35% w/v for hydrochloric acid — that is, the actual HNO<sub>3</sub>:HCl mass ratio is less than 1:2,</ref> optimally in a volume ratio of 1:3. It was named so because it can dissolve the so-called royal or [[noble metal]]s, [[gold]] and [[platinum]]. However, [[titanium]], [[iridium]], [[ruthenium]], [[tantalum]], [[osmium]], [[rhodium]] and a few other metals are capable of withstanding its corrosive properties.<ref>''Encyclopædia Britannica Online''. "[http://www.britannica.com/EBchecked/topic/31021/aqua-regia Aqua regia]".</ref> | |
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| ==Applications==
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| Aqua regia is primarily used to produce [[chloroauric acid]], the [[electrolyte]] in the [[Wohlwill process]]. This process is used for refining highest quality (99.999%) gold.
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| Aqua regia is also used in [[Chemical milling|etching]] and in specific [[Analytical chemistry|analytic procedures]]. It is also used in some laboratories to clean [[laboratory glassware|glassware]] of [[organic compound]]s and metal particles. This method is preferred over the "traditional" [[chromic acid]] bath for cleaning [[NMR tube]]s, because no traces of paramagnetic [[chromium]] can remain to spoil spectra.<ref>Hoffman, R., [http://chem.ch.huji.ac.il/nmr/preparation/preparation.html How to make an NMR sample], [[Hebrew University]], 10 March 2005. Accessed 31 October 2006.</ref> While [[chromic acid]] baths are 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 due to mishandling.<ref>[[American Industrial Hygiene Association]], [http://www.aiha.org/insideaiha/volunteergroups/labHandScommittee/Pages/IncidentsExplosions.aspx Laboratory Safety Incidents: Explosions]. Accessed 8 September 2010.</ref>
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| Due to the reaction between its components resulting in its [[#Decomposition of aqua regia|decomposition]], aqua regia quickly loses its effectiveness (yet remains a strong acid), so its components are usually only mixed immediately before use.
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| While local regulations may vary, aqua regia may be disposed of by careful neutralization, before being poured down the sink. If there is contamination by dissolved metals, the neutralized solution should be collected for disposal.<ref>{{cite book | title = Prudent Practices in the Laboratory: Handling and Disposal of Chemicals | year = 1995 | publisher = National Academies Press | author = Committee on Prudent Practices for Handling, Storage, and Disposal of Chemicals in Laboratories, National Research Council | pages = 160–161 | url = http://www.nap.edu/catalog.php?record_id=4911 | format = free fulltext}}</ref><ref>{{cite web | publisher = Princeton University | title = Aqua Regia | work = Laboratory Safety Manual | url = http://web.princeton.edu/sites/ehs/labsafetymanual/cheminfo/aquaregia.htm}}</ref>
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| ==Chemistry==
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| ===Dissolving gold===
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| [[File:Golddust.jpg|thumb|right|Pure gold precipitate produced by the aqua regia chemical refining process]]
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| Aqua regia dissolves gold, 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 [[ion]]s (Au<sup>3+</sup>). The hydrochloric acid provides a ready supply of chloride ions (Cl<sup>−</sup>), which react with the gold ions to produce tetrachloridoaurate(III)ion [[anion]]s, also in solution. The reaction with hydrochloric acid is an equilibrium reaction which favors formation of chloroaurate 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. The gold dissolves to become [[chloroauric acid]]. In addition, gold may be dissolved by the free chlorine present in aqua regia. Appropriate [[Chemical equation|equations]] are:
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| :Au ''(s)'' + 3 {{chem|NO|3|−}}''(aq)'' + 6 {{chem|H||+}} ''(aq)'' → {{chem|Au||3+}} ''(aq)'' + 3 {{chem|NO|2}} ''(g)'' + 3 {{chem|H|2|O}} ''(l)'' and
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| :{{chem|Au||3+}} ''(aq)'' + 4 {{chem|Cl||−}} ''(aq)'' → {{chem|AuCl|4|−}} ''(aq)''.
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| The oxidation reaction can also be written with [[nitric oxide]] as the product rather than [[nitrogen dioxide]]:
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| :Au ''(s)'' + {{chem|NO|3|−}} ''(aq)'' + 4 {{chem|H||+}} ''(aq)'' → {{chem|Au||3+}} ''(aq)'' + NO ''(g)'' + 2 {{chem|H|2|O}} ''(l)''.
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| If the aqua regia solution only contains gold, solid [[tetrachloroauric acid]] may be prepared by boiling off excess aqua regia, and removing residual nitric acid by repeatedly heating with hydrochloric acid. That step reduces nitric acid (see [[#Decomposition of aqua regia|Decomposition of aqua regia]]). If elemental gold is desired, it may be selectively reduced with [[sulfur dioxide]], [[hydrazine]], [[oxalic acid]], etc.<ref name = ullgold>{{Ullmann | doi = 10.1002/14356007.a12_499 | title = Gold, Gold Alloys, and Gold Compounds | first1 = Hermann | last1 = Renner | first2 = Günther | last2 = Schlamp | first3 = Dieter | last3 = Hollmann | first4 = Hans Martin | last4 = Lüschow | first5 = Peter | last5 = Tews | first6 = Josef | last6 = Rothaut | first7 = Klaus | last7 = Dermann | first8 = Alfons | last8 = Knödler | first9 = Christian | last9 = Hecht | displayauthors=8}}</ref>
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| ===Dissolving platinum===
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| [[File:Platin loest sich in heissem Koenigswasser.JPG|thumb|left|Platinum being dissolved in aqua regia]]
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| 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.
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| :Pt ''(s)'' + 4 {{chem|NO|3|-}} ''(aq)'' + 8 H<sup>+</sup> ''(aq)'' → Pt<sup>4+</sup> ''(aq)'' + 4 NO<sub>2</sub> ''(g)'' + 4 H<sub>2</sub>O ''(l)''
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| :3Pt ''(s)'' + 4 {{chem|NO|3|-}} ''(aq)'' + 16 H<sup>+</sup> ''(aq)'' → 3Pt<sup>4+</sup> ''(aq)'' + 4 NO ''(g)'' + 8 H<sub>2</sub>O ''(l)''
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| The oxidized platinum ion then reacts with chloride ions resulting in the chloroplatinate ion.
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| :Pt<sup>4+</sup> ''(aq)'' + 6 Cl<sup>−</sup> ''(aq)'' → {{chem|PtCl|6|2-}} ''(aq)''
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| 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.
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| :2Pt ''(s)'' + 2HNO<sub>3</sub> ''(aq)'' + 8 HCl ''(aq)'' → (NO)<sub>2</sub>PtCl<sub>4</sub> ''(s)'' + H<sub>2</sub>PtCl<sub>4</sub> ''(aq)'' + 4 H<sub>2</sub>O ''(l)''
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| :(NO)<sub>2</sub>PtCl<sub>4</sub> ''(s)'' + 2 HCl ''(aq)'' <math>\rightleftharpoons</math> H<sub>2</sub>PtCl<sub>4</sub> ''(aq)'' + 2 NOCl ''(g)''
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| The chloroplatinous acid can be oxidized to [[chloroplatinic acid]] by saturating the solution with chlorine while heating.
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| :H<sub>2</sub>PtCl<sub>4</sub> ''(aq)'' + Cl<sub>2</sub> ''(g)'' → H<sub>2</sub>PtCl<sub>6</sub> ''(aq)''
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| Dissolving platinum solids in aqua regia was the mode of discovery for the most dense metals, [[iridium]] and [[osmium]], both of which are found in platinum ore and will not be dissolved by the acid, instead collecting on the base of the vessel.
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| As a practical matter, when platinum group metals are purified through dissolution in aqua regia, gold (commonly associated with PGMs) is precipitated by treatment with [[iron(II) chloride]]. Platinum in the filtrate, as hexachloroplatinate(VI), is converted to [[ammonium hexachloroplatinate]] by the addition of [[ammonium chloride]]. This ammonium salt is extremely insoluble, and it can be filtered off. Ignition (strong heating) converts it to platinum metal:<ref>{{cite journal|first1 = L. B.|last1 = Hunt|last2 = Lever |first2= F. M.|journal = Platinum Metals Review|volume = 13|issue = 4|year = 1969|pages = 126–138|title = Platinum Metals: A Survey of Productive Resources to industrial Uses|url = http://www.platinummetalsreview.com/pdf/pmr-v13-i4-126-138.pdf}}</ref>
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| :3 (NH<sub>4</sub>)<sub>2</sub>PtCl<sub>6</sub> → 3 Pt + 2 N<sub>2</sub> + 2 NH<sub>4</sub>Cl + 16 HCl
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| Unprecipitated hexachloroplatinate(IV) is reduced with elemental [[zinc]], and a similar method is suitable for small scale recovery of platinum from laboratory residues.<ref>{{cite journal | journal = Inorg. Synth. | title = Recovery of Platinum from Laboratory Residues | author1 = George B. Kauffman | author2 = Larry A. Teter | doi = 10.1002/9780470132388.ch61 | series = Inorganic Syntheses | year = 1963 | last3 = Rhoda | first3 = Richard N. | isbn = 9780470132388 | volume = 7 | pages = 232}}</ref>
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| ===Reaction with tin===
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| Aqua regia reacts with [[tin]] to form [[tin(IV) chloride]], containing tin in its highest oxidation state:
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| : 4 HCl + 2 HNO<sub>3</sub> + Sn → SnCl<sub>4</sub> + NO<sub>2</sub> + NO + 3 H<sub>2</sub>O
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| ===Decomposition of aqua regia===
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| 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.
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| :HNO<sub>3</sub> ''(aq)'' + 3 HCl ''(aq)'' → NOCl ''(g)'' + 2[Cl] ''(g)'' + 2 H<sub>2</sub>O ''(l)''
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| 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.
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| :2 NOCl ''(g)'' → 2 NO ''(g)'' + Cl<sub>2</sub> ''(g)''
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| Because nitric oxide reacts readily with atmospheric [[oxygen]], the gases produced also contain [[nitrogen dioxide]], NO<sub>2</sub>.
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| :2 NO ''(g)'' + O<sub>2</sub> ''(g)'' → 2 NO<sub>2</sub> ''(g)''
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| ==History==
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| [[File:Musaeum Hermeticum 1678 p 398 III. Clavis AQ27.tif|thumb|The fox in Basil Valentine's Third Key represents aqua regia, ''Musaeum Hermeticum'', 1678]]
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| Aqua regia first appeared in the work of medieval European alchemist [[Pseudo-Geber]], dating from the 14th century.<ref>[http://www.1911encyclopedia.org/Alchemy Encyclopædia Britannica 1911, ''Alchemy'']</ref> The third of [[Basil Valentine]]’s keys shows a dragon in the foreground and a rooster eating a fox eating a rooster in the background. The rooster symbolizes gold (from its association with sunrise and the sun’s association with gold), and the fox represents aqua regia. The repetitive dissolving, heating, and redissolving (the rooster eating the fox eating the rooster) leads to the buildup of chlorine gas in the flask. The gold then volatilizes in the form of gold chloride, whose red crystals were known as dragon’s blood. The reaction was not reported in modern chemical literature until 1890.<ref>{{cite book|last=Principe|first=Lawrence M.|title=The secrets of alchemy|year=2012|publisher=University of Chicago Press|location=Chicago|isbn=0226682951}}</ref>
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| [[Antoine Lavoisier]] called aqua regia nitro-muriatic acid in 1789.<ref>''Elements of Chemistry'', p. 116</ref> When [[Operation Weserübung|Germany invaded Denmark]] in World War II, Hungarian chemist [[George de Hevesy]] dissolved the gold [[Nobel Prize]]s of German physicists [[Max von Laue]] (1914) and [[James Franck]] (1925) in aqua regia to prevent the Nazis from confiscating them. The German government had prohibited Germans from accepting or keeping any Nobel Prize after jailed peace activist [[Carl von Ossietzky]] had received the Nobel Peace Prize in 1935. De Hevesy 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. They re-cast the medals and again presented them to Laue and Franck.<ref>[http://www.archive.org/stream/adventuresinradi01heve#page/27/mode/1up/search/medals "Adventures in radioisotope research"], George Hevesy</ref><ref>{{Cite web| publisher = The Nobel Foundation | url = http://nobelprize.org/nobel_prizes/about/medals/ | author = Birgitta Lemmel | title = The Nobel Prize Medals and the Medal for the Prize in Economics | year = 2006}}</ref>
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| == See also ==
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| * ''[[Aqua fortis]]''
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| * ''[[Aqua vitae]]''
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| * [[Digger gold]]
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| * [[Sulfuric acid]]
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| ==Notes==
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| {{Reflist|group=note}}
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| ==References==
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| {{Reflist|2}}
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| ==External links==
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| * [http://jchemed.chem.wisc.edu/JCESoft/CCA/CCA3/MAIN/AQREGIA/PAGE1.HTM Chemistry Comes Alive! ''Aqua Regia'']
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| * [http://www.periodicvideos.com/videos/mv_aqua_regia.htm Aqua Regia] at ''[[The Periodic Table of Videos]]'' (University of Nottingham)
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| * [http://www.youtube.com/watch?v=XoqU1GfIOkI Demonstration of ''Gold Coin Dissolving in Acid (Aqua Regia)'']
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| {{DEFAULTSORT:Aqua Regia}}
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| [[Category:Gold]]
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| [[Category:Alchemical substances]]
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| [[Category:Oxidizing mixtures]]
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| [[Category:Oxidizing acids]]
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| [[Category:Mineral acids]]
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