science experiment: Emerald City Pennies
Courtesy of Bedon's Discovery Workbook
Do you know the story of The Wonderful Wizard of Oz? When Dorothy, the Scarecrow, the Tin Man, and the Cowardly Lion arrive in the wizard's Emerald City, they find that everything's green: the houses. the streets, the clothing the people wear-even the pennies are green! You can make real pennies turn green, and you don't need to borrow Dorothy's green eyeglasses to do it. All it takes is a little vinegar and a little patience.
What you need:
-2 clean, shiny pennies
-vinegar, about 1/4 cup
1. Draw and color a picture of the pennies. What color crayons or markers come closest to the color of the real coins?
2. Fold the paper towel in half, and then fold it in half again to make a square.
3. Put the folded paper towel in the bottom of the bowl.
4. Slowly pour the vinegar into the bowl until the paper towel is completely soaked. (Make sure there is no puddle of extra vinegar sitting on top of the paper towel)!
5. Put the pennies on top of the wet paper towel and leave them there overnight.
6. The next day, take the pennies out of the bowl. Did they change on both sides or just one side?
7. Draw and color the pennies the way they look now. What color crayons or markers do you need this time?
The main ingredient in pennies is a metal called copper. It's copper that gives pennies their reddish-brown color. Vinegar contains a chemical called acetic acid. When acetic acid touches copper, something new is created-a green-blue chemical called carbon acetate. In science, we call this kind of change a chemical reaction. The chemicals in the vinegar and in the copper react (change) when they are combined, making carbon acetate on the pennies.
Did you notice that the top of the pennies changed color, but not the bottoms? That's because this chemical reaction can only happen if something else is available-oxygen from the air around us. The tops of the pennies are exposed to the air and so oxygen is available to be part of the chemical reaction. The bottoms of the pennies don't change because they don't have enough oxygen next to them to make the reaction possible.