We love simple STEM activities for kids that you can do at home. One summer, we completed 31 STEM activities for kids all in the same month! For one of our 31 days of STEM activities, of course, we had to learn how to turn a penny green as a science experiment.
I love science experiments for kids that are easy but have impressive results like this how to turn a penny green science project, plus kids get to learn why pennies turn green at the same time!
You’ll also want to check out the ultimate list of summer STEM activities and the ultimate list of summer science experiments.
Why is the Statue of Liberty Green? Science Project
We’ve all seen the statue of liberty, and she is quite green these days. But originally, she was bright orange and a shiny copper! The green stuff covering the statue of liberty is called malachite, and it is a result of copper being exposed to salt, acid, and weather.
You can recreate Liberty’s transformation from copper to green with pennies. Read on to learn how to turn a penny green.
Why Do Pennies Turn Green?
Pennies are largely made of copper, which means they oxidize just like many other metals.
However, rather than rusting, pennies simply get covered in a coating of green that can be polished off. Turning a penny green does not eat holes into the penny.
When you add vinegar and salt to pennies, it dissolves the top copper-oxide layer of the penny. This causes the copper atoms to mix with oxygen in the air and chlorine in the salt.
This creates a blue-green substance known as malachite. It’s chemistry in action!
However… our penny experiment actually took much longer than we expected! Our hypothesis was that since pennies have a bit less copper now, perhaps that is why they took longer to react.
The other hypothesis was that it was user error. For more fun chemistry science experiments, try making classic borax slime, making salt crystal feathers, and making fizzing rainbows!
What Kids Learn when Turning Pennies Green
Kids learn a lot when learning how to turn pennies green. They learn about chemical reactions, mixing atoms, how malachite is made, the principles of corrosion, and a whole lot more!
If you’d like more simple science activities, try the color mixing flower, salt crystal feathers, the flower discovery table, or rainbow slime!
How to Turn a Penny Green Science Project Materials
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- Salt
- Vinegar
- Shallow tray
- Paper towels
- Pennies (we used a mix of old and new to see if there was a difference in when or how they would turn green)
Morton Morton Salt, 26 ozBounty Select-a-Size Paper Towels, White, 12 Huge Rolls
Member’s Mark Distilled White Vinegar Jug, 1 gal
Lakeshore Easy-Clean Craft Trays – Set of 4
How to Make a Penny Green
Soak a paper towel in vinegar and line the bottom of your tray.
Place the pennies onto the paper towel. Sprinkle the pennies with salt.
When possible, it’s best to mix several elements of STEM together, using elements of science, technology, engineering, and math all at once. You’ll maximize the learning of children and help them understand how all the elements of STEM activities work together.
How Long Does it Take for a Penny To Turn Green?
In the wild, so to speak, pennies turn green with exposure to oxygen and an acid (which can be from fingers, food, the weather, and a bunch of other stuff). But in this controlled environment, you can speed up the process using salt, vinegar, and some air.
Allow the pennies to sit until they start to turn green.
This could take as little as 24 hours, but in our case, it took over 2 weeks.
However, we did have the pennies soaking in a deep solution at first. When we changed it out for a vinegar-soaked paper towel, the pennies turned green the next day.
I think our original set-up didn’t get enough oxygen, which is essential for turning a penny green.
