Electroplating: Copper-plating Nails and Cleaning Pennies

We talked about electrolysis and electroplating, and we wanted to try zinc-plating a penny as described here, here, and here. The hard part is getting the zinc for dissolving in your solution. We tried using the zinc casing from our dissected battery, but for some reason that didn't work. We could have tried to track down some hydrochloric acid and copper sulfate to use instead, but that seemed like too much trouble when we could demonstrate the concept another way.

So, first we cleaned pennies to show how copper oxide (that greenish stuff, like rust but called "verdigris," that forms on old copper) dissolves in a vinegar and salt solution. (Instructions are here.) You can clean pennies by dipping them in the solution, like this:

A half-dipped penny---you can see the difference between cleaned and uncleaned!

If you leave the pennies soaking in this solution for awhile, they get all shiny and clean. Then, if you remove them from the solution and DON'T rinse them with water, the copper quickly begins to oxidize again and the greenish-blue verdigris starts to form. You can see it clearly on these pennies above. Interestingly, this is the same chemical reaction that forms malachite and azurite!

After you've soaked the pennies, many of the copper ions have left the outside of the pennies and have become suspended in your solution. So, once the pennies are out, you can put in some small steel nails or paper clips. After awhile, the suspended copper ions (positively charged) will attach themselves to the (now negatively charged, from sitting in the solution and giving up some of their positive ions) steel nails. If you leave them in long enough, your steel nails and paper clips will end up plated with a thin layer of copper! It looks really pretty.

(unplated paper clip on the left, for comparison)

The longer you leave them in, the brighter and more noticeable the copper plating will become! These were left in for a few days.

This isn't truly electroplating, because there was no electric current in the solution to help facilitate the process. But you can see how electroplating works based on this---the current just pushes the ions off the anode and makes the object to be plated into a cathode, so it will attract those ions. Very cool!