Pennies tend to turn brown because their copper becomes oxidised over time. Because this "tarnish" is not the same as dirt, cleaning pennies with regular soap and water is not likely to work. Juice is actually a good cleaning agent, due to its acid content. While all experiments that seek to determine which juice best cleans pennies are the same at their root, there are some variations that make good projects for school.
Overnight Experiment With Different Juices
This straightforward experiment determines which juice works best for cleaning pennies. Fill roughly five different glasses with different kinds of juice. You can use apple, orange, grapefruit, peach or any other fruit juice. Drop an oxidised penny in each glass and leave it overnight. Remove the pennies from the glasses and rinse them with water. Which penny is the cleanest? Why do think this juice best cleaned the penny?
Overnight pH Experiment With Different Juices
This project is a variation on Section 1. Before you put the pennies into the glasses, dip a piece of pH paper into each juice. Which juice is the most acidic? Which is the most alkaline? Record the results in a chart. Do you think the most acidic juice will be the best cleaning agent? Put the pennies in the glasses overnight. See which penny is cleanest and compare to your hypothesis. Did the most acidic juice clean the best? If so, what does that tell you? If not, what can you conclude about the role of acid in cleaning copper?
Measure Cleaning Time With Juice
Take three pennies and lay them on a surface. Choose three acidic juices such as lemon, orange and grapefruit. Place a drop of the first juice on the first penny, a drop of the second juice on the second penny and a drop of the third juice on the third penny. Observe the pennies and see which starts to change colour first. Measure the acid levels of the juices with pH paper. Did the most acidic juice clean the fastest?
Cleaning Pennies With Other Liquids
This experiment works well in conjunction with any of the experiments above, particularly if you have found that acid is not the best cleaner. Drop pennies in different liquids overnight, but go beyond juice. Try vinegar, cola, sugary drinks, low-acid tomato juice, ketchup, soy sauce, bleach or anything else. Which liquids worked best? Do these liquids have something in common? What can you conclude?