Everybody realizes that as coins, like pennies, stay in circulation the "look" older - but what is really happening? This is a question that also begs us to ask - can an old penny be restored to look new? The answer is yes, with a nice little chemistry experiment.
Here's what you need.
What to do.
Put the teaspoon of salt in the glass bowl and add the vinegar. Stir until you can't see the salt anymore (because it has dissolved into the vinegar). Once you've done this, you are ready to clean pennies. While on TV we cleaned only a couple of pennies, you can do interesting things if you clean a bunch of them - try 25 or 30 pennies and watch them all get clean.
Once you've cleaned a large number of pennies you can do a couple of extra experiments.
Add-on #1. This experiment is designed to see what happens if you let the chemistry experiment continue. Take half of the pennies you cleaned and rinse them with a lot of water (and put them someplace to dry, like on a paper towel.) Take the other half and put them somplace to dry, but do not rinse them. You will have to wait for a while - maybe an hour or two (which is why we couldn't do this part on TV) - to see any difference between the two groups of pennies, but the difference is pretty amazing by that time.
Add-on #2. The "other" part of the experiment - the vinegar and salt solution that was used to "clean" the pennies is also useful for an additional experiment. In this experiment, take a clean nail (you might want to use steel wool to "clean" the outside of it) and place it in the vinegar and salt solution AFTER you have finished cleaning the group of pennies. It will take a little while but look at the nails and see what's happening as they sit in this solution.
Some Links
Copper Caper - a nice site about this experiment from the Exploratorium.
Exloring Acid Rain - An extra experiment you can do with your new "clean" pennies.
Adding pH to the Experiment - This site adds Cabbage indicator to the experiment to study the role of acid vs. base