National Engineers Month

	Activities by Grade	K - 2		5 - 8
		3 - 4		9 - 12

Polishing Pennies

How can you make an old penny shine again?

What you need:

• 6 old, dull pennies
• 5 paper cups
• lemon juice
• milk
• cola
• apple juice
• water
• 5 plastic spoons
• paper towel

Directions:

1. Put a penny in each cup.
2. Pour some lemon juice into the first cup.  Make sure that the penny is completely covered.
3. Wait a few minutes. Then remove the penny. What does it look like?  Record your observations on the chart in the box under "lemon juice."
4. Rub the penny on a paper towel.  What happens?
5. Try it again using the other liquids!  To one cup add milk.  To the next cup add cola.  To the next cup add apple juice, and to the last cup add water.  Use the same amount of each liquid.
6. Wait about 5 minutes. Then take a look. Which pennies are shiny?  Which liquids make the pennies shine the most?

Observations

More:

Keep experimenting to find the best way to polish a penny!  What happens if you use a different liquid, like soap or vinegar?  (Ask an adult to help you choose a liquid to test.) Or, what happens if you put a penny in a liquid for a longer period of time, like a day or a week?  Choose one thing to change (that’s the variable), and make a prediction.  Then test it!

Engineering Scoop:

A new penny is partly made from bright, shiny copper.  But after a while, it loses its shine.  Why?  Because the copper mixes with oxygen in the air and makes a coating of copper oxide.  When you put a penny in lemon juice, the dull coating of copper oxide goes away. That's because lemon juice is an acid.  Acids can dissolve copper oxide. Which other liquids did you find make a penny shiny?

© 2001 WGBH Educational Foundation