3. Pour vinegar over the pennies so that the paper towel is fully saturated.
Leave the experiment out for a few days, adding more vinegar as the paper towel began to dry out and flipping the pennies over occasionally. The longer you wait, the more green they become!
Question to Spark Curiosity & Critical Thinking
What happened to the pennies over time? What is your theory as to why this happened?
Can you think of any other chemical reactions you’ve seen in everyday life?
What’s Going On
A chemical reaction as occurred! (A chemical reaction is the combination of two reactants to form something entirely new.) A penny is made of copper. The vinegar on the paper towel helps the copper in the penny easily react with the oxygen in the air to form a blue-green colored compound called malachite.
This is similar to why the Statue of Liberty (which is covered with a layer of copper) has turned greenish-blue. The statue would naturally turn greenish-blue due to exposure to the oxygen in the air. However, because some rain has acid from pollution in it, the rain speeds up the reaction (just as the vinegar caused the reaction with the penny).
Want to go even further?
Even more activities to inspire creativity and critical thinking for various ages.
- Try a similar experiment: Fill a cup with 1/4 cup vinegar and 1 teaspoon salt. Stir. Add some pennies and let them sit for 5 minutes. Take them out and rinse them. What happened?
- Make a volcano using baking soda and vinegar.