Polishing Pennies

In this experiment, learners try different liquids to see which ones clean pennies best. Liquids to try include water, lemon juice, cola, vinegar, and dishwashing detergent. Suggested extensions include trying vinegar with table salt, vinegar with cream of tartar, salt, and dishwashing detergent, tomato ketchup, and water and baking soda. Learners should find that acidic liquids are better cleaners, since they react with the copper under the "dirty" outer layers of copper oxide, allowing the "dirty" parts to be rubbed away. This activity could be combined with a lesson about the Statue of Liberty, which is made of copper and shows signs of copper oxide on its surface.