Cleaning Pennies Activity

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Updated on Mar 12, 2014

Has your kid ever looked at a collection of change in a jar or on the kitchen counter and asked why some coins are darker than others? Chances are you replied that some coins are older than others. The scientific truth is that copper atoms in the penny are attracted to oxygen atoms in the air which interact and form copper oxide. Some pennies look dull and dirty because they are covered with this infamous copper oxide. Our cleaning copper coins experiment is a great way to show your kid how to get those dingy pennies looking nice and new again.

What You Need:

  • 20 dull and dirty pennies
  • ¼ cup white vinegar
  • 1 teaspoon salt
  • A clear shallow bowl (not metal)
  • Paper towels
  • Spoon

What You Do:

  1. Put the salt and vinegar into the bowl and stir until it dissolves.
  2. Put the pennies into the bowl for about 5 minutes. Watch them when they first go in. What do you see?
  3. Take half the pennies out and place them on a paper towel.
  4. Take the second half out and rinse them off very well. Place them on a paper towel and mark it as being “rinsed.”
  5. Wait about an hour and then check back on your two piles. What differences does your child see between the two? Record the differences and make some guesses about why they are different. The rinsed pennies should be bright and look brand new.

What Happened? When the vinegar and salt dissolve the copper oxide they make it easier for the copper atoms to join with the oxygen in the air and the chlorine in the salt. If the pennies are not rinsed it allows a chemical reaction to occur that produces a greenish-looking compound called malachite.