Materials:
Old, Grungy Pennies, glass jar, and vinegar
Procedure:
Put the pennies in the jar. Pour in the vinegar. Make sure the pennies are completely covered. Wait for about 15 minutes.
The pennies were grungy because of a Chemical Reaction of the copper and oxygen which formed Copper Oxide. Vinegar is an acid. It reacts to the Copper Oxide, making a new chemical, Copper Acetate. The old, grungy pennies after about 15 minutes should now look shiny and new.