Gold doesn't dissolve in acid...then it does...then it comes back...

The most potentially expensive demonstration that I've ever done was to take my gold wedding ring (not pure gold, 14K, I think) and placing it in concentrated hydrochloric acid. The activity series says that nothing should have happened, and - thankfully because I certainly hadn't cleared the demo with my wife first - nothing did. That's because I used only hydrochloric acid.

Using hydrochloric acid and nitric acid, though. Agua regia (royal water) will dissolve gold, producing - as the video above shows - chloroauric acid.

To see that gold really is non-reactive in each of the acids (and in molten NaOH, even) alone, check out the video after the jump.

I've also added a video showing how the gold can be recovered from the chloroauric acid.





...now, let's see how to get the gold back out of the acid...