STEM Lab: Why the Statue of Liberty is Green

By Jen Anderson March 18, 2015

Did you know that you can clean your money? Make your dirty pennies bright and shiny with a little chemistry!

What You Need:

  • Old dirty pennies (at least 10)
  • Table salt
  • White vinegar
  • Bowl of water
  • Paper towels for drying

What You Do:

  1. Put all your pennies in a non-metal bowl and cover them with salt.
  2. Pour white vinegar on top.
  3. Rub the mixture over the pennies with your fingers. You can also just let them sit for a minute or so.
  4. Remove half the pennies from the vinegar and rinse them in a bowl of water, then dry them with a paper towel.
  5. Remove the rest of the pennies from the salt/vinegar mix and put them directly on a dry paper towel without rinsing them in water. Let these sit for about an hour while you have a snack, go for a bike ride, or play a board game.

The Science Behind the Fun:

Pennies get dingy and dirty because the copper reacts with oxygen in the air to form copper oxide. The salt/vinegar mix works to remove it.

The pennies that didn't get rinsed off should develop a blue-green layer. When it isn't rinsed away, the salt/vinegar mix speeds up the formation of copper oxide, which is a blue-green color. This is the same reaction that makes the Statue of Liberty appear to be green!