Most people ask what type of juice cleans pennies because they or their child are performing a science experiment about the difference between acids and bases. The simple answer is that more acidic juices will clean pennies well and basic juices will have a much lesser effect. However, the simple answer is not particularly interesting. It is far more rewarding to find out exactly what works and what doesn't.
All modern day pennies have a copper coating on the outside, and those dated before 1982 are made of pure copper. The copper comes in contact with the oxygen in the air and forms a chemical bond with it. The result is the compound, copper oxide. Copper oxide has a cloudy gray or green appearance which makes pennies look dirty over time. Soap and water will not wash this substance off because it is not water soluble. Instead, it is necessary to alter the chemical bonds by adding an acid to the mix. This acid will react with the oxide and dissolve it off of the penny's surface.
So What Type of Juice Cleans Pennies?
Some juices will have almost no effect on pennies, while others will clean off the copper oxide completely, revealing a shiny penny that looks just like new. More basic juices include grape juice and apple juice. At the acidic end are tomato juice, grapefruit juice, orange juice, lime juice and lemon juice. Berry juices lie somewhere in the middle. The peak performer will be pickle juice, which is not a juice at all but in fact very highly acidic vinegar. Most experimenters find that lemon juice will be a strong second runner up.
How to Test
Since it's always more fun to find out firsthand than to simply read an article, why not conduct the experiment? All that's needed is about a cup of each of the above juices, a mason jar for each juice, PH paper and 18 oxidized pennies. It's okay to substitute other juice types if the exact ones mentioned are not available.
Once the materials are ready, follow these steps:
- Pour each juice into a mason jar and label it with a piece of tape.
- Dip a piece of PH paper into each jar. The bluer it turns, the more basic the juice. The redder it turns, the more acidic. Set the papers aside to dry and then label each.
- Drop two pennies into each jar and seal it tightly.
- Let the pennies sit in their respective juices overnight. Refrigerating the jars is optional.
- Check the results the next day and compare them to each juice's PH.
- Rank the appearance of each penny from one to five and see how it corresponds to acidity.
PH paper is simply paper treated with a substance capable of distinguishing acidity. It's available at stores that sell scientific supplies and can also be ordered online.
After figuring out what type of juice cleans pennies, pull the pennies out of the jars, rinse them under warm water and set them on a paper towel to dry. Then glue the pennies and the corresponding PH paper to a board to present the results to others.
While this experiment is a good way to teach kids about chemistry it is not a good way to clean pennies that are collector's items. In fact, cleaning old coins in any way can severely reduce their sale value. A better thing to do in this situation is to take the pennies to a professional restorer. This person may be able to "fix" the pennies without changing their chemical makeup.