Gold Coin Dissolving in Acid (Aqua Regia)


Warning: This reaction produces toxic gases and uses corrosive acids. It should be performed in a fume hood with gloves. Greetings fellow nerds. In this video we’re going to dissolve a gold coin in acid. Here is the coin. It’s a 1/20th troy ounce canadian maple. Now we add 10mL of concentrated 12M hydrochloric acid. By itself the acid does not react with the gold so we add another 1mL of concentrated 15M nitric acid. The mixture is gently heated to speed up the reaction. Eventually the mixture will turn yellow and bubble as the gold starts dissolving. We showed in a previous video that gold will not dissolve in either hydrochloric acid or nitric acid alone. What’s happening here is that the nitric acid is first oxidizing the surface of the gold. Then the chloride ions in the hydrochloric acid reacts with the gold ions to form a complex ion that dissolves away into solution. The nitric acid then further oxidizes the surface and the process repeats. Other oxidants also work but nitric acid is the easiest to work with. The bubbles you’re seeing are nitrogen dioxide gas along with some nitrosyl chloride, chlorine and nitrogen monoxide. This mixture of hydrochloric and nitric acid is also known by the name of aqua regia. Aqua regia does not destroy all metals though. I showed in a previous video that ruthenium is totally immune to aqua regia. Hmm, looks like the reaction is slowing down, I’m going to add another 1mL of nitric acid. Overall what we’re producing in this reaction is chloroauric acid. There is a famous story among chemists: During world war II hungarian chemist George de Hevesy dissolved the gold Nobel Prizes of German physicists Max von Laue and James Franck in aqua regia to prevent the Nazis from finding them. This deep orange solution was what they would have seen on the shelf. All the gold atoms are still there as ions, and they can easily be returned to metal with the proper reducing agent. Looks like the reaction is complete. We have destroyed a gold coin and converted it to chloroauric acid using aqua regia. Leaving it for a few weeks in a desiccator bag we can dry it and produce this solidified form of chloroauric acid. Thanks for watching.

52 thoughts on “Gold Coin Dissolving in Acid (Aqua Regia)

  1. It was found by aqua regia Abu Musa Jabir bin Khayyam. And he is a Muslim.(Türkish) Kral suyunu Cabir Bin Hayyam bulmuştur. Müslüman simyager.

  2. AQUA RGIA was actually prepared by Abu Mūsā Jābir ibn Hayyān (c. 721 – c. 815) and he was a Muslim lived and died in Kufa city/ IRAQ. At the time of his discovery, he named this new acid in Arabic "The royal water الماء الملكي".

  3. It seems to me that it would be easier to dissolve the coin if you did a couple of things. First, use a 1g Maple instead of a 1/20oz. Maple. It's a smaller, thinner coin. Gold is very malleable so you could hammer the shit out of it on an anvil until you get a much thinner coin. It might be too much work to make a foil out of it, but the much larger and thinner piece of gold could be folded up and put into solution. Maybe the whole reaction could be done at room temperature so you wouldn't have to watch it all the time.

  4. 0:50 – The reaction mechanism is wrong! There is formed an atomic chlorine. Which also reacts with gold.

  5. can someone clear my doubt ? in my textbook it is said that 3 parts of conc.hcl and one part of conc.nitric acid to prepare aqua regia …is it wrong?

  6. I smelt with lead, then remove the lead by cupel. Left with a mixed metal button. End result need the gold. I need to remove other metals first, then AR for the gold.Any idea's on how? Thank's

Leave a Reply

Your email address will not be published. Required fields are marked *