Dirty Pennies

Students prepare to oxidize pennies!Background Information

Have you ever seen a penny that was so dirty it was black or green instead of copper? The pennies are dirty from being used, but there is more causing them to dull. It’s a chemical reaction called oxidation! Pennies slowly react with air and they oxidize. That is why older pennies are dull and green, while new pennies are shiny. But this isn’t permanent, you can clean them and make them shiny again!




Materials Needed

  • A few dull, dirty pennies

  • 1/4 cup white vinegar

  • 1 teaspoon salt

  • A glass or clear bowl

  • 2 clean steel nails

  • A clean steel screw

  • Paper towels

Initial Investigation

  1. Put the salt and vinegar in the bowl. Stir until the salt dissolves.

  2. Dip one penny halfway into the liquid. Hold it there for about 10 seconds, then pull it out. What do you see?

  3. Talk with your group about what happened. Described what happened in your note book.


  1. Dump all the pennies into the liquid. You can watch them change for the first few seconds. After that you won't see anything happen.

  2. After 5 minutes, take half of the pennies out of the liquid. Put them on a paper towel to dry.

  3. Take the rest of the pennies out of the liquid. Rinse them really well under running water, and put them on a paper towel to dry.

  4. Write "rinsed" on the second paper towel.

  5. Put a nail and a screw into the liquid. Lean another nail against the side of the bowl so that only part of it is in the liquid

  6. After 10 minutes, take a look at the nails. Are they a different color than they were before? Is the leaning nail 2 different colors? If not, leave the nails in the bowl and check on them again in an hour or so.

  7. What's happening to the screw? You may see lots and lots of fizzing bubbles coming from the threads. Is the screw changing color? Leave it in the liquid for a while and see what happens.

  8. After about an hour, look at the pennies on the paper towels. What's happened to the ones you rinsed? What's happened to the others?

  9. What color is the paper towel under the unrinsed pennies?

This experiment was originally published by the Exploratorium

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