Cleaning Pennies

This is a simple observation experiment you can do on your own.  No adults needed!

Your Materials For This Science Experiment & Steps Combined

1. Ketchup
Soak your pennies in ketchup to clean them like new. Well, after you wash the ketchup off, that is. The salt and acetic acid in vinegar do the trick.

2. Hot Sauce
Hot sauce, like Tabasco or taco sauce, also will remove the oxides off pennies. As in ketchup, salt and vinegar are both in hot sauce.

3. Coke
Coke and off-brand colas will quickly remove the tarnish. Just don't drink the coke afterward. Coke contains phosphoric acid that cleans the oxides.

4. Citrus Juice
Try a variety of citrus juices to see which works best or simply let your pennies soak in lemon juice. Citric acid works similarly to the other acids.

5. Pencil Eraser
Use a common pencil eraser on your pennies to remove the oxides like mistakes on paper. This takes more work than the others, however. The friction does the work.

6. Vinegar and Salt
Make a solution of vinegar and salt and let the pennies soak. The acid in vinegar, like in citrus, is what really takes the tarnish away.

Here's what's happening:

The oxygen in the air and the copper in the pennies form an oxide that coats the pennies and makes them look dirty. The acids (usually vinegar - acetic acid) break the copper oxide free from the penny. As we have seen experimentally, acid alone does not clean as well as acid and salt. It appears, the salt breaks down somewhat, freeing chlorine ions into the solution.

The chlorine ions bond with the copper in solution forming some sort of copper chloride, allowing the acid to break more of the copper oxide free from the penny.

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