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.