As it heats the zinc will diffuse into the copper, forming brass on the surface that looks like gold.Įventually it will wear off but the results are rather impressive. Simply wash the coin and place it on a hotplate heated to about 300 Celsius. The most amazing trick is to turn it into gold. This is thermodynamically more favorable than pure separate metals and thus serves as the driving force.Īnyway, whatever the specific chemical reason, we've now deposited zinc onto copper. The silvery color you're seeing on the penny is actually a type of white brass, not pure zinc. Coinage metals (copper, silver, and gold) are often found as important components of most catalysts and are known for their high activity and important properties. Others state that it's an alloy of zinc metal and copper on the surface. Keywords: copper silver gold catalysis selectivity Catalysts are materials that allow important reactions to be more selective, faster and require less energy.
#THE COINAGE METALS COPPER SILVER AND GOLD FREE#
What is the driving force? I've searched the literature and there doesn't seem to be a consensus among scientists, some claim it's a surface free energy issue with zinc having a lower potential on copper than in free solution (at high concentration). Overall we're going from zinc metal to zinc metal and at first it seems like we're missing something about thermodynamics. Now the smart physical chemist might wonder how this can possibly work. The zinc ions in solution now redeposit form a thin layer of zinc metal. The zinc metal dissolves and releases electrons that go into the copper and give it a negative charge. They must touch the zinc in order for this reaction to work. The solution is heated to a boil and copper pennies, that have been thoroughly washed/cleaned, are dropped in. Zinc metal was obtained from our video on getting useful materials from batteries: Then we drop in several cut strips of zinc metal. This can be made by simply mixing hydrochloric acid with zinc metal and waiting until the fizzing stops. If you don't have zinc sulfate or can't make it, you can also use zinc chloride.
Zinc sulfate was made back in our video on making a copper sulfate and Obviously it's a chemistry trick but still impressive.įirst we get 30g of zinc sulfate and dissolve it into 100mL of water. In a display of alchemy we turn copper pennies into silver and finally to gold.
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