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What is Aqua Regia?

Aqua regia is a mixture of  nitric and hydrochloric acid concentrations, usually one portion of the former by volume to three portions of the latter. The alchemists gave this mixture its name (literally, "royal water") due to its ability to dissolve gold and other so-called noble metals.

In analytical procedures for the solution of certain iron ores, phosphate rocks, slags, nickel-chromium alloys, antimony, selenium, and some of the less soluble sulfides, such as those of mercury, arsenic, cobalt, and lead, Aqua regia, and other similar mixtures are used.

These metals are classified as noble metals, so the title 'royal water' was granted to the solution that could dissolve them. Aqua regia is not a single chemical, but rather a combination of two acids, hydrochloric acid (HCl) and nitric acid (HCl) (HNO3). The product is more effective in the case of aqua regia than the number of its pieces, which is what makes it so beneficial.

Here, will study aqua regia solution, aqua regia gold, aqua regia chemical name and aqua regia acid in detail.

Acid that Dissolves Gold

There can be several metals in either an elemental form or ionic form. The basic form, solid gold, is uncharged to illustrate this lack of charge, chemists add a superscript "0" to the chemical symbol: for gold, this would be Au0.   Anything called an oxidizer can cause electrons to be lost to the Au0 molecules, converting them into Au3+, a positively charged ion. Nitric acid is an example of a strong oxidizer which, when combined, can turn Au0 into Au3+. The positive gold ions then dissolve into the liquid solution and become a part of it. On its own, before the reaction enters balance, nitric acid can only dissolve a very tiny amount of the gold atoms into Au3+.

The hydrochloric acid separates into H+ and Cl- ions once the hydrochloric and nitric acids are combined in aqua regia. Due to the attraction of opposite ions, the Cl- ions can then respond to Au3+ to form AuCl4- (also called tetrachlorogold). Because the Au3+ is now part of the tetrachlorogold, the solution is removed. This disrupts the balance and enables the nitric acid to continue to dissolve more Au0 into Au3+. This is an example of the Le Chatelier Principle, which essentially shows that if a reaction's products are consumed, it allows the reaction to continue making more products. This is also known as aqua regia gold. This is one of the uses of Aqua Regia.

Aqua Regia Handling

  1. Glass (preferably Pyrex) containers should always be used. Some plastics are melted by aqua regia and most metals are corroded. 

  2. Never store solutions of aqua regia. Mix up only what you need, then after each use, destroy. 

  3. With the sash between you and the solution, mix the solution into a hood. Wear splash gloves, face shield, lab coat, and appropriate gloves for chemical splashes. 

  4. Always add the nitric acid to the hydrochloric acid slowly when preparing the aqua regia solution. 

  5. Toxic gases are released by dissolving metals in aqua regia, always working with aqua regia in a fume hood. 

  6. The solution of Aqua regia is very energetic and potentially explosive. It is very likely that it will get hot, over 100 0C. Handle with care.

  7. The exothermic reaction will be accelerated by adding any acids or bases to Aqua Regia or spraying it with water. 

  8. Till it cools, leave the hot aqua regia solution in an open container. 

  9. Never store Aqua Regia in a container that is closed. Over time, it will oxidize to form toxic nitrosyl chloride, chlorine gases, and nitrogen dioxide. This will create pressure in the container, probably causing an explosion to occur. 

  10. An explosion may occur by mixing aqua regia with organic compounds.

Did You Know?

Do not store aqua regia. Owing to the oxidation of its reactive components, aqua regia quickly loses its effectiveness. For each use, blend a fresh solution. With sodium bicarbonate, excess solutions should be neutralized and disposed of via the drain, followed by flushing with large amounts of water.

The spent solution should be neutralized with sodium bicarbonate after the substance has cooled and disposed of through the drain, followed by flushing with plentiful quantities of water. The neutralized solution should be collected as a toxic waste if the solution is polluted with heavy metals (i.e., silver, chromium).

FAQs (Frequently Asked Questions)

1. How hazardous is aqua regia?

The solution of aqua regia is very vigorous, very likely to become hot (> 100 oc), and potentially explosive. aqua regia solutions are highly corrosive. Corrosive materials can, through chemical act at the contact site, cause degradation of living tissue and can be solids, liquids, or gases.

2. Is aqua regia the most potent acid?

No acid is able to dissolve these metals on its own. The chemical burn hazards of two extremely corrosive strong acids are mixed in aqua regia, so it's one of the worst acids purely on that basis. However, the risk does not stop there, because aqua regia loses its potency quickly-remaining a powerful acid.

3. Why is aqua regia so powerful?

It is possible to describe an acid in many aspects. One way to describe it is something that increases the hydrogen ion concentration in the solution. Aqua regia is a mixture of two powerful acids, hydrochloric acid (HCl) and nitric acid (HNO3), which form an intensely acidic solution.