Chemistry For Pennies (Literally)

           

Supplies:

Three dirty old pennies | Measuring spoons

Vinegar | Lemon juice | Ketchup | Salt

Clean, new steel nails

Three small non-metal cups (small, recycled plastic containers are great)

Craft sticks for stirring | Paper towel | Pencil

 

Pour a tablespoon of vinegar into a small plastic cup. Add one-fourth teaspoon of salt. Stir until the salt dissolves. Put the first penny into this solution. What do you see? Leave the penny in there for five minutes. Then take it out and let it dry on the paper towel. Write "vinegar" underneath it.

 

The reason pennies get dull is that the copper in them gradually reacts with the air to form "copper oxide." Pure copper is bright and shiny, but the oxide that comes from contact between copper and oxygen is a dull, brown color.

 

Do NOT throw out the vinegar-salt solution. Instead, lean a steel nail against the side of the plastic container so that the metal is half in, and half out of the vinegar-salt solution. Leave the nail there for 10 minutes. You may see some bubbles! That means a chemical reaction is taking place. Is the nail in two tones now? That's because the copper that the vinegar removed from the penny has now shifted to the surface of the nail.

 

Now try the penny-shining test in another container with a tablespoon of lemon juice and a quarter-teaspoon of salt, and a third container with the same quantities of ketchup and salt. There's a lot of acid in lemon juice as well as in the tomatoes that are the main ingredient of ketchup. Rinse the craft stick you use for stirring with water in between stirring tasks.

 

Leave the two other pennies in the lemon juice and ketchup solutions for five minutes. Remove. Place them on the paper towel, labeling them underneath as "Lemon Juice" and "Ketchup," so you can remember which is which.

 

Which type of acid worked best? Why do you think?

 

If you have an old toothbrush around, polish your pennies even more with a little more vinegar, lemon juice or ketchup, and some salt. The friction (FRIC-shun) from rubbing the toothbrush bristles should make the pennies even shinier.