Turning pennies green is a way to teach children the basics of chemical reactions. Unlike some chemical reactions, the process of turning a penny green is a fairly quick one, which a child can easily monitor the progress of. This helps keep children interested, even younger ones. This makes a good science experiment for those working on science class presentations, teachers trying to introduce students to chemistry, and Girl and Boy Scout leaders preparing an educational lesson.
Place a penny into each small paper cup, if you're going to give one to each student. If you're just trying to turn a lot of pennies green, spread them evenly onto a foil-lined brownie pan.
Sprinkle salt onto the top of each penny, using about a half teaspoon per penny.
Pour vinegar onto the salt-covered pennies. Use enough to cover the pennies completely.
Examine the pennies periodically. In about a week, they should all be green.