Clean Coins: A Quick STEM Activity for Preschool

by Meghan

Sharing is caring!

Our preschool is teaching the kids about money this month with it’s no cost fundraiser, Coin Wars. So we have had coins sorted and lying around all month, waiting to be donated. To reinforce what the girls were doing at school, we have been playing and learning with the coins at home too with quick STEM activities for preschool, like this Clean Coins Experiment.

What liquid will clean coins best? A simple science experiment for preschoolers to introduce the scientific method - ask a question, make a guess, test, and review your results. | Preschool | STEM | STEAM | Science Project | Money | Kids Activities |

Simple and Quick STEM Activities for Preschoolers

Preschoolers have a natural curiosity about the world around them… just ask any mom of a three year old how many questions a day she gets! You can leverage this interest for learning, and even introduce the basic tenets of the scientific method. Last week, our simple preschool STEM activities tested the surface tension of water with drops on a coin. This week, we are seeing what liquids best remove tarnish from old coins.

Question: What cleans coins the best?

For this simple and quick STEM activity for preschoolers, we tested the cleaning power of four everyday liquids on old pennies to see which one left coins the cleanest. We used water, vinegar, soda and lemonade.

Hypothesis: Which liquid do you think will clean coins best?

Before we started, I asked the girls which liquid they thought would get the dirty coins the most clean. Big M, my 5 year old said vinegar “because you use it for cleaning things.” She’s an observant one!

My 3 year old, Lil’ M, said “water because we take a bath in it.” Neither of them thought soda or lemonade would clean anything because “they have sugar and leave things sticky.” Love to see how these little scientific minds think!

Conduct an Experiment

With our question formed and guesses made, it was time for the simple science experiment. For this experiment, you only need a few simple supplies.


4 glass cups (you can use plastic, those some liquids may damage plastic when left to sit overnight)
12-16 pennies
Safety goggles

The girls put 3-4 coins in 4 small glasses. Then, they added one of the liquids to each glass. They took turns pouring the liquids in the glasses – and of course, wore their safety goggles as they poured.

They closely observed the glasses to see if they could see any ‘science happening’. They noticed bubbles forming on the coins in the soda glass.

We left the coins to soak in the cups overnight.


The next morning we drained the cups, rinsed off the coins and made our final observations.

Collect Data and Form Conclusion

After carefully observing all 4 sets of coins from the different cups, the girls agreed that the vinegar cleaned the coins best.

Why? The ‘dirt’ on coins comes from oxidation – the impact of oxygen from the air reacting with the metal, copper, of the penny, forming copper oxide, the black tarnish you see on the coins before cleaning them. Acids, like vinegar, help breakdown the copper oxide on the surface of the coin, removing it and leaving them shiny again.

More Quick STEM Activities for Preschool

Want to make them really shine? Try adding salt to your acids (vinegar, lemonade, lemon juice or orange juice). Want to turn your copper pennies green? Try this cool science experiment from Little Bins for Little Hands. For a simpler preschool STEM activity with coins, try our Drops on a Coin activity to test surface tension and fine motor skills. Stay tuned for more simple fun with coins coming up this week!

For more awesome quick STEM activities for preschool, be sure to follow our Preschool and STEM for Kids – Science boards on Pinterest.

Love it? PIN THIS!

What liquid will clean coins best? A simple science experiment for preschoolers to introduce the scientific method - ask a question, make a guess, test, and review your results. | Preschool | STEM | STEAM | Science Project | Money | Kids Activities |


Sharing is caring!


More to love on Playground Parkbench


President's Day Preschool - Never a Doll Moment February 28, 2021 - 5:02 pm

[…] to the science table where a coin cleaning experiment was performed on them. These directions from Playground Parkbench are great. Our “science mom” went a step further and explained that substances like […]


[…] Cleaning Coins from Playground Parkbench […]

19 STEM Activities For Kids You Can Do At Home - Perfection Pending June 28, 2018 - 2:57 pm

[…] Clean Coins […]

SCIENCE for Preschoolers - Cleaning Pennies - Sixth Bloom- Lifestyle, Photography & Family Blog June 1, 2018 - 2:20 pm

[…] love how Playground Parkbench tried four different liquids to see which cleaned the BEST!  I think for a bit older kids (elementary age) this would be a […]

The Best STEM Activities for Kindergarten October 27, 2017 - 5:07 am

[…] Cleaning Coins from Playground Parkbench […]

Teaching Money: 20+ Kids Activities Beyond Counting Coins March 16, 2017 - 11:38 am

[…] For Kids […]

Cool Science for Kids with Pennies March 10, 2017 - 4:47 pm

[…] For Kids […]


Leave a Comment

* By using this form you agree with the storage and handling of your data by this website.