Aqua regia, a powerful blend of hydrochloric acid and nitric acid, is known for its ability to dissolve precious metals like gold and platinum. It gets its name from its capability to dissolve metals that are considered royal or noble. The aqua regia is made by mixing nitric acid and hydrochloric acid in a 1:3 ratio.
Making ProcedureÂ
1. First put on the appropriate safety equipment including gloves, safety goggles, and lab coat.
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2. To determine the quantity of hydrochloric acid, use a glass or plastic container. For safety reasons, it is important to pour the acid into the water instead of the reverse to prevent any hazardous splashing or potential heat production.
3. To achieve the desired strength of the mixture, you can adjust the ratio of nitric acid to hydrochloric acid by adding the appropriate amount of nitric acid to the hydrochloric acid.
4. The mix hydrochloric acid (HCL) and nitric acid (HNO3). The resulting mixture could have a yellow or orange hue and will release unpleasant fumes.
Note- This blend is an extremely potent acid and has the potential to cause severe harm if not handled correctly. Only skilled experts must utilize it within a suitable laboratory while taking appropriate safety measures.
PropertiesÂ
- Formula: HNO₃ + 3HClÂ
- Boiling Point: 108 °CÂ
- Melting point: -42 °CÂ
- Vapor pressure: 2.1KpaÂ
- Density: 1.21 g/cm³Â
- ChemSpider ID: 56437Â
- Solubility: Soluble in waterÂ
Reaction with Gold
Aqua regia, a potent acid, has the remarkable ability to dissolve gold. This unique property makes it a popular choice for purifying and analyzing precious metals. The process of the reaction between aqua regia and gold involves a series of distinct steps.
Hydrochloric acid in aqua regia reacts with gold to form gold chloride (AuCl3) and hydrogen gas (H2).Â
Au + 3HCl → AuCl3 + 3H2
Nitric acid present in aqua regia reacts with gold chloride to form nitrosyl chloride (NoCl) and regenerate hydrochloric acid:Â
AuCl3 + 4HNO3 → 3HCl + Au(NO3)4 + 4NO2
A single reaction can be written as, the net reaction between aqua regia and gold:Â
Au + 3HNO3 + 4HCl → AuCl3 + 3NO2 + 4H2O
The gold chloride that is produced can dissolve in water and is later separated from the solid residue through filtration. Following this, the gold is separated from the chloride solution using different techniques.
Aqua Regia Reaction with Platinum Equation
Platinum, just like gold, can be dissolved by aqua regia due to its noble metal properties. The reaction between platinum and aqua regia is quite similar to that of gold.
\[Pt + 4HNO_3 + 6HCl → H_2[PtCl6] + 4NO_2 + 4H_2O\]
In this reaction, hydrochloric acid and nitric acid in aqua regia react with platinum to form hexachloroplatinate(IV) acid, also known as chloroplatinic acid, and nitric oxide gas and water.