Facts about Aqua regia.
Facts about Aqua regia
The name "Aqua regia" is a latin word, which means "royal water" or "regal water". Its name is "Aqua regia" because royal metals of the periodic table, such as gold and platinum, can dissolve in it. Aqua regia can dissolve noble metals such as gold and platinum, but it can't dissolve tantalum, iridium, and some other metals.
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| (Aqua regia solution in a beaker) |
Aqua regia is a very strong acid. It is a chemical composition of nitric acid (HNO3) and hydrochloric acid (HCl) in a 1:3 molar ratio.
About the Father of Aqua regia :-
Aqua Regia was discovered by "Abu Musa Jabir ibn Hayyan" (also known as "Jabir ibn Hayyan" and "Gaber"). He was a Persian alchemist. (He is also known as the father of chemistry). Geber was discovered aqua regia around the year 800AD, when he mixed common salt (NaCl) with vitriol [ Sulfuric acid (H2SO4) was known as "vitriol" in encient times ]. This was the way that the alchemist tried to find aqua regia at that time.
Formation and Decomposition of Aqua regia :-
The chemical reaction of concentrated HNO3 and HCl gives water and volatile products such as nitrosyl chloride (NOCl) and chlorine gas. So that the aqua regia appears smoky and yellow color.
HNO3(aq) + 3 HCl(aq) ➝ HOCl(g) + Cl2(g) + 2 H2O(l)
When volatile products escape from aqua regia, it loses its energy and nitrosyl chloride (NOCl) decomposes into nitric oxide & chlorine gas.
2 NOCl (g) ➝ 2 NO(g) + Cl2(g)
The smoke over the aqua regia is a combination of chlorine gas and nitrogen dioxide gas. Here nitrogen dioxide gas is produced from nitric oxide. After nitric oxide is formed, it reacts with atmospheric oxygen to give nitrogen dioxide.
2 NO(g) + O2(g) ➝ 2 NO2(g)
Reaction of Aqua regia :-
(1) Dissolving of Gold :-
When we add gold to an aqua regia solution, it gives chloroauric acid, nitrogen dioxide (or, nitric oxide), hydronium ion and water.
Au(s) + 3 HNO3(aq) + 4 HCl(aq) ⇌ [AuCl4]¯(aq) + 3 NO2(g) + [H3O]^+(aq) + 2 H2O(l)
Or,
Au(s) + HNO3(aq) + 4 HCl(aq) ⇌ [AuCl4]¯(aq) + NO(g) + [H3O]^+(aq) + H2O(l)
This is how gold dissolves in aqua regia solution.
(2) Dissolving of Platinum :-
Platinum also reacts with aqua regia. When platinum reacts with aqua regia it gives chloroplatinous acid (H2PtCl4), nitrosoplatinic chloride ((NO)2PtCl4) & water.
2 Pt(s) + 2 HNO3(aq) + 8 HCl(aq) ➝ (NO)2PtCl4(s) + H2PtCl4(aq) + H2O(l)
Again, (NO)2PtCl4 reacts with HCl and gives chloroplatinous acid & nitrosyl chloride.
(NO)2PtCl4(s) + 2 HCl(aq) ⇌ H2PtCl4(aq) + 2 NOCl(g)
Chloroplatinous acid can again be oxidised to chloroplatinic acid (H2PtCl6), when it is heated with chlorine gas.
H2PtCl4(aq) + Cl2(g) ➝ H2PtCl6(aq)
This is the process in which platinum dissolves into aqua regia.
(3) Reaction with Tin :-
Aqua regia also reacts with tin to give tin(IV)chloride, nitrogen dioxide, nitric oxide & water.
Sn + 4 HCl + 2 HNO3 ➝ SnCl4 + NO2 + NO + 3 H2O
(4) Reaction with Iron pyrite (FeS2) :-
When aqua regia reacts with iron pyrite, it gives nitric oxide, sulphuric acid, ferric chloride and water.
FeS2 + 5 HNO3 + 3 HCl ➝ FeCl3 + 2 H2SO4 + 5 NO + 2 H2O
Some Other Information About Aqua regia :-
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| (Chemical formula of Aqua regia) |
The chemical formula of aqua regia is HNO3 + 3 HCl. It looks as a red, orange or yellow fuming liquid. Its melting point and boiling point are 231K and 381K respectively. The IUPAC name of aqua regia is nitric acid hydrochloride. It is also known as nitrohydrochloric acid and royal water.
Use of Aqua regia (Application) :-
Aqua regia is mainly used in the extraction and purification of gold and platinum (it gives 99.99% of pure gold and platinum). It is also used in metal etching and analytical processes.
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