President's Day Science Fun

You might think that there isn't a way to celebrate President's Day with science projects, but you'd be wrong.  Everyday, you are likely to encounter the face of Abraham Lincoln or George Washington...on a coin!  Here are some fun and easy science activities that use coins.

Green and Clean Pennies
Supplies
4 or more pennies (some from before 1982)
Vinegar
Salt
2 small, non-metal bowls
Paper Towel

Process
1. Put a piece of the paper towel in the bottom of each bowl.
2. Place two pennies in each bowl.
3. In the first bowl, pour in a little bit of vinegar to soak the paper towel.  Allow the bowl to sit for an hour.
4. In the second bowl, pour in some vinegar and salt.  Swirl the bowl to dissolve the salt.  The vinegar and salt dissolve the outer layer of dirt on the pennies.  It should take about 30 seconds for them to start to shine.  Flip them over and wait another 30 seconds.
5. Remove the pennies from the second bowl, rinse them with water, and let them dry.  You now have two clean, shiny pennies!
6. After an hour, the pennies in the first bowl should be starting to turn green.

What is happening?
In the first bowl, the vinegar speeds up a chemical reaction that happens between pennies and oxygen called oxidation.  When copper oxidizes, it turns a greenish color, forming a compound called malachite.  There is more copper in pennies created before 1982, so the reaction is more visible.

In the second bowl, the vinegar and salt create a chemical reaction that dissolves the copper oxide (the dirty spots) and some of the copper on the outside of the penny, giving you a shiny penny.

Flowers and Copper
Supplies
Fresh flowers
2 glass cups
Water
1 penny from before 1981
Toothpaste

Process
1. Prepare your coin.  Use a small bit of toothpaste to clean the coin by rubbing the toothpaste onto the penny and letting it sit for three minutes.  Rinse the toothpaste off.
2. Trim your flowers to fit the two cups.
3. Put about an inch of water into each container.  Make sure the same amount of water is in each cup.
4. Place flowers in each container.  One container is the "control".  This container will not have a coin in it, so that we can see what happens to the flowers with no intervention.  The other container is the "variable".  Put your penny at the bottom of the variable container.  Keep both containers in the same place.
5. Observe what happens to the flowers over the next seven days.

What is happening?
Copper has antibacterial properties, which can potentially keep flowers fresh longer by killing germs that would break the flowers down faster!

Coin Power
​Supplies
6-8 pennies
6-8 nickels
Strip of aluminum foil
Paper towels
¼ cup white vinegar
1 tablespoon of salt
Multimeter (voltage tester)
Small LED pin light (optional)
Small bowl
Small plate

Process
1. In a small bowl, combine the salt and vinegar and stir until the salt is dissolved.
2. Cut the paper towels or paper napkins into small squares slightly smaller than the coins. You will need at least 20 squares.
3. Dip the squares into the vinegar and salt mixture.
4. Place a dry paper towel on a plate. Take a strip of aluminum foil that's about 1 inch x 3 inches and fold it lengthwise in thirds. Place the foil on the paper towel. Then layer the coins and the paper on top of the foil in a pattern: first a penny, then paper, then a nickel. Repeat the pattern until you run out of paper squares. The stack should have a penny on the bottom and a nickel on the top. The paper squares should not overlap or hang over the edge of the coins.
5. Test the voltage of the battery. Touch the black lead to the strip of the aluminum foil and touch the red lead to the nickel on the top of the stack. Set the multimeter to a low voltage of direct current.

What is happening?
Nickels are made of a mixture of metals, including zinc. Pennies are made from several metals, including copper. Both zinc and copper conduct electricity. When two different metals are connected by an electrolyte (in this experiment, it's the vinegar and salt solution), a chemical reaction occurs at the surface of the metals. The metals are the electrodes. When these electrodes are connected by a wire, they create an electrical current.

For more fun coin activities, check out the U.S. Mint's kid webpage!