What is aqua regia ? Mention it's uses.
Answers
Answer:
Aqua regia (/ˈreɪɡiə, ˈriːdʒiə/; from Latin, lit. "regal water" or "king's water") is a mixture of nitric acid and hydrochloric acid,[note 2] optimally in a molar ratio of 1:3. Aqua regia is a yellow-orange (sometimes red) fuming liquid, so named by alchemists because it can dissolve the noble metals gold and platinum, though not all metals.
Aqua regia is primarily used to produce chloroauric acid, the electrolyte in the Wohlwill process for refining the highest quality (99.999%) gold.
Aqua regia is also used in etching and in specific analytic procedures. It is also used in some laboratories to clean glassware of organic compounds and metal particles. This method is preferred[by whom?] over the more traditional chromic acid bath for cleaning NMR tubes, because no traces of paramagnetic chromium can remain to spoil spectra.[1] While chromic acid baths are discouraged[according to whom?] 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.[2]
Due to the reaction between its components resulting in its decomposition, aqua regia quickly loses its effectiveness (yet remains a strong acid), so its components are usually only mixed immediately before use.
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.[3][4]
Dissolving gold[edit]
Pure gold precipitate produced by the aqua regia chemical refining process
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 ions (Au3+). The hydrochloric acid provides a ready supply of chloride ions (Cl−), which react with the gold ions to produce tetrachloroaurate(III) anions, also in solution. The reaction with hydrochloric acid is an equilibrium reaction that favors formation of chloroaurate anions (AuCl4−). 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 chlorine present in aqua regia. Appropriate equations are:
Au + 3 HNO
3 + 4 HCl
↽ − ⇀ {\displaystyle {\ce {<=>>}}}
[AuCl
4]−
+ 3 [NO
2] + [H
3O]+
+ 2 H
2O
or
Au + HNO
3 + 4 HCl
↽ − ⇀ {\displaystyle {\ce {<=>>}}}
[AuCl
4]−
+ [NO] + [H
3O]+
+ H
2O.
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). If elemental gold is desired, it may be selectively reduced with sulfur dioxide, hydrazine, oxalic acid, etc.[5] The equation for the reduction of gold by sulfur dioxide is:
2 AuCl−
4 (aq) + 3 SO
2(g) + 6 H
2O (l) → 2 Au (s) + 12 H+
(aq) + 3 SO2−
4(aq) + 8 Cl−
(aq).
Dissolving platinum[edit]
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−
3 (aq) + 8 H+ (aq) → Pt4+ (aq) + 4 NO2 (g) + 4 H2O (l)
3Pt (s) + 4 NO−
3 (aq) + 16 H+ (aq) → 3Pt4+ (aq) + 4 NO (g) + 8 H2O (l).
The oxidized platinum ion then reacts with chloride ions resulting in the chloroplatinate ion:
Pt4+ (aq) + 6 Cl− (aq) → PtCl2−
6 (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 (H2PtCl4) and nitrosoplatinic chloride ((NO)2PtCl4). 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:
2Pt (s) + 2HNO3 (aq) + 8 HCl (aq) → (NO)2PtCl4 (s) + H2PtCl4 (aq) + 4 H2O (l)
and
(NO)2PtCl4 (s) + 2 HCl (aq) ⇌ H2PtCl4 (aq) + 2 NOCl (g).
The chloroplatinous acid can be oxidized to chloroplatinic acid by saturating the solution with chlorine while heating:
H2PtCl4 (aq) + Cl2 (g) → H2PtCl6 (aq).
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.
Answer:
aqua regia is a compound of many acids which is also called kings water. it is used for purifying gold and other precious metals as it cleans away the top layer of the metal
Explanation:
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