Here’s a simple chemistry project for kids to explore – make old pennies shiny and clean again with salt and vinegar!
Why do pennies look dull and brown as they age? Well, the copper in pennies reacts with the oxygen in the air to form a new molecule – copper oxide. This is the tarnish on the surface of a penny. Kids will be impressed with this simple science demonstration that makes pennies clean again!
You will need:
- Dull, brown pennies
- A paper plate
- A small bowl
- Paper towels
- A dropper
Before trying to clean the pennies with salt and vinegar, have your kids try to wash them with soap and water. Soap and water won’t clean the pennies because oxidation is a chemical change. Washing pennies with water is a physical change. The pennies will need a chemical reaction to make them shiny again!
We tried shaking salt onto the pennies and then squirting vinegar on them with a dropper.
It was amazing to watch the pennies turn copper colored again wherever the salt and vinegar touched them!
Why does this work? The salt and vinegar (acetic acid) dissolve the copper oxide. Pretty neat!
We also tried putting salt and vinegar in a bowl, stirring it up, and then dipping the pennies in the solution. We tried dipping a penny halfway in the solution to see if we could get it to be half shiny and half dull…
And it worked!
So cool! And it was really amazing how quickly the chemical reaction dissolved away the tarnish!
We rinsed our pennies afterward because the salt and vinegar is kind of sticky, and I found out later after reading this article that we could have observed another neat chemical process if we had NOT rinsed them.
Have fun exploring!
Here’s another post with chemistry ideas: Colorful Chemical Reactions
Mea Jul 2, 2016
Catsup works too- same principal I'm sure :)
Learned that working at A&W jn high school.
Lindsey Jun 8, 2022
I don’t know if it’s the case with a U.S Penny but in the UK a 2p coin (copper) when wet will create a chemical reaction with limescale on taps to dissolve the limescale residue and leave your faucet (tap) like new!
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