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Polishing Pennies Experiment

Polishing Pennies Experiment - TheHomeschoolScientist.com

When pennies are made, the copper on their surface is bright and shiny. Over time, the copper oxidizes and becomes dull and dark. Sometimes they even turn green. In this polishing pennies experiment, we will test different liquids to determine if any of them can make the dull pennies shiny again.

The Experiment

1.  Choose 3 dark, aged pennies and one new shiny penny to compare them to. Make a note of the color of each.

2.  Pour 3 different liquids into small cups. We used vinegar, ketchup and milk. You might consider lemon juice or soda. Place one penny into each liquid.

 3.  After 5 minutes, remove the pennies and make a note of the color.

4.  Put the pennies back and wait another 10 minutes. Remove the pennies and make a note of the color.

5.  Wipe each penny with a cloth and, once again, make a note of the color.

What Happened

Acids found in various liquids react with the copper oxide and cause it to dissolve revealing the shiny copper underneath. All the liquids we tried in our experiment contain an acid in varying forms and strengths. Try this experiment at home with various liquids to see which acid polishes pennies the best. Use this printable to record your findings.

Polishing Pennies Experiment Printables





  1. This looks like a great activity, but bear with me, I’m a little cloudy on the chemistry principle that this is illustrating. Acid removes oxidation, yes, but why? Is this because it affects the bonding or charge or something like that? Can you elaborate on the broader concept or chemistry rule?

    • Acids in solution ionize into charged ions. When we measure the pH of a solution, we are actually measuring the H+ ions in that solution. These H+ atoms are what react with the copper oxide forming a copper salt and water. The chemical formula looks like this:

      copper oxide + acid => copper salt + water
      CuO (s) + H2 —> Cu (s) + H2O

      Does that help?

  2. I love that you included the chemical formula in the comment to answer her. When I was in high school I used to love working on chemical formulas.

    I’m such a nerd.

    Thanks for linking up to Science Sunday!

  3. Yeah thats cool and all, but my 4th grade year my class did something different. Why not do something different than that? If you want to make a penny a lot more shiny to see it’s copper color then you should use vinegar and salt! I call that “Shiny Penny”. You put the penny or pennies inside with the vinegar and salt, you mix it for 5 minutes then you soak it for 10. BAM! Look at the results ! Try it out. You’ll be amazed!!!!


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