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Did You Know There Is Such A Thing As Gold Acid?

Illustration for article titled Did You Know There Is Such A Thing As Gold Acid?

If you want to find out what’s unusual about chloroauric acid, look at the “Au” in the middle. It indicates that this is an acid made using gold. We’ll tell you why people make this acid, and how it can hurt you.


Gold is tough to make into an acid because it’s tough to dissolve. For a long time, no one believed it could be dissolved at all. Gold symbolized immortality because it couldn’t be degraded or corroded. Eventually alchemists found a way to corrode it.

Aqua regia is a mixture of nitric acid and hydrochloric acid. It delivers a one-two punch. The nitric acid sets gold atoms loose, and rips three electrons off of each of them. The hydrochloric acid supplies four negatively charged chlorine atoms and a hydrogen atom. The resulting mixture, when boiled down, results in solid crystals of chloroauric acid.

Illustration for article titled Did You Know There Is Such A Thing As Gold Acid?

This is not something you want to mess with. It’s fitting that something that pretty to look at will go for your eyes. Traces of the acid are extremely corrosive to the eyes, but they’ll attack any part of the body they come in contact with. Incautious people can inhale the fumes from the acid. Some people even ingest it. Not only does the acid damage the tissues in the digestive system but the gold can impair kidney function.

So why make gold acid? Mostly chloroauric acid is a midpoint in the gold recovery process. When companies recover gold from old computer equipment, this is the stuff process they use, corroding gold until it forms a solid precipitate, and then separating the gold out from the chlorine and the hydrogen. So as cool as gold acid sounds (and I am hoping a Bond villain uses it at some point), it’s only a temporary by-product.

Top Image: April Nobile / ©, Vial: W. Oelen

[Source: Hydrogen tetrachloroaurate, The Formula for Aqua Regia]


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An article about aqua regia and not even an aside on how it saved two Nobel prizes from the Nazis? For shaaaaame.…

...By the time the Nazis arrived, both awards had liquefied inside a flask that was then stashed on a high laboratory shelf....

Back in Denmark, de Hevesy did a remarkable thing. He reversed the chemistry, precipitated out the gold and then, around January, 1950, sent the raw metal back to the Swedish Academy in Stockholm. The Nobel Foundation then recast the prizes using the original gold and re-presented them to Mr. Laue and Mr. Franck in 1952.