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Have you ever wondered how to clean pennies? Cleaning copper pennies can be a lot of fun for kids! You can turn them from a dull brown to bright and shiny.
I decided to turn it into science experiment to test a few different substances and see what works best to clean old brown pennies. I remember accidentally doing this one time with a packet of hot sauce from Taco Bell when I was in high school. That’s where this experiment idea came from! My friends & I thought it was so cool that the penny got so shiny.
Why Do Pennies Turn Brown?
Pennies are made of copper. When copper is exposed to oxygen it will corrode (turn brown) because of chemical reactions. The brown coating is called patina. These are copper oxide molecules and they actually protect the metal underneath. Over time, copper transitions from its shiny brown color to a darker brown shade.
How to Clean Pennies:
If you are genuinely wanting to know how to clean pennies, I have learned that the combination of vinegar and salt will get them really clean and shiny. Especially if you scrub the pennies with that combination a bit. But for the sake of this experiment, we wanted to try some different substances to see what would work best for us. I let my kids help pick the different things to test.
We filled some cups with a small amount of different substances in our kitchen to see which one would get our dirty pennies the cleanest. I had my kids each take a guess at which thing would get the pennies the cleanest. They were way off, so it was fun to see which really did get them clean. We let the pennies soak for a time, then put them on a paper towel to dry. Next wipe or scrub the penny clean with paper towels.
Substances We Tested for Cleaning Pennies
When experimenting with how to clean pennies, we tested a variety of items, here are some ideas:
Lemon or lime juice
Put some of each substance in a a bowl or cup, enough to cover the penny, then allow it to sit for a time. We left ours for 30 minutes.
We took them out and wiped each one off on a paper towel. You can see the surface of the pennies change and become shinier. You can then rinse them with running water and set them on a towel to dry.
Vinegar and lemon juice both work really well for cleaning pennies. But, ketchup was the clear winners for our pennies, with soy sauce next, maybe with a little more time they would have gotten a little bit cleaner.
This is a fun experiment to try with younger kids! My kids of all ages were interested in the results, though. So if you want to do it with older kids, just go deeper with the science!
Use my Scientific Method Worksheets to extend this!
See even more STEM projects for kids.
Now just for the sake of preserving history, here is our original image from the first time we tried this experiment about 10 years ago. 🙂