Make Gold from Chloroauric Acid

Warning: This demonstration uses corrosive acids and produces toxic gases. This should be performed with gloves in a fume hood. Greetings fellow nerds. In this video we’re going to make elemental gold from chloroauric acid by reduction with sodium metabisulfite. But first I need to crush your expectations We’re not making gold from nothing. These atoms of gold are already present in the chloroauric acid as ions. Chloroauric acid itself is made from gold or gold containing reagents. It is not possible to chemically make an element like gold from substances that do not already contain atoms of it. Our objective here is to explore the chemistry of gold and demonstrate a particular step in its refining. So here is the original vial of solidified chloroauric acid we made in a previous video containing 1.5 grams of elemental gold. Now our reducing agent will be 4 grams of sodium metabisulfite. And we’ll be dissolving that in 10mL of water. About 2mL of water is added to the chloroauric acid to dissolve it. Now the sodium metabisulfite is added in drop by drop. There we go. Already you can see the reaction starting. What’s happening is the sodium metabisulfite is reacting with the chloroauric acid to produce elemental gold, hydrochloric acid and sodium bisulfate. That brown precipitate you’re seeing is actually the gold. It doesn’t look like common gold because the particles of gold produced here are so small and rough that they don’t reflect light in the way smooth bulk gold does. Okay let me speed this up until all the sodium metabisulfite is added and all the gold has settled. And here we are about an hour later with most of the extremely fine gold dust settled to the bottom. We vacuum filter the mixture and there is our gold. We wash it a few times with water to ensure all the chemicals are gone and then let it dry. And here is the gold transferred to a vial. It’s actually quite crumbly when dry and some hard shaking will break up the sponge into a powder. To get the shine of common gold we have to melt it down. Now I can’t do that myself since I don’t have a torch hot enough for it but I know another youtube channel called indeeditdoes who will do it for me. So here is his sample of 1.5g of gold made in the same way as I did and now he’s heating it with a powerful oxy-propane torch that can heat the gold well past its melting point of 1064 degrees celsius. It takes several minutes to adequately heat the gold but eventually it will liquefy and coalesce into one solid bead of gold. And there it is. A cool way to make small nuggets of gold is to directly pour the molten gold into a tall container of water. As it falls it cools and solidifies into tiny shiny nuggets of gold. And here they are after drying. So there you have it. We have made elemental gold from chloroauric acid. Thanks for watching. And if you want to see more about the practical side of gold refining, check out the channel indeeditdoes. He's got a lot of videos about gold refining and just precious metal recovery in general. In this video we'll look at the chemical resistance of gold. In this video we're going to dissolve a gold coin in acid.