Experiments for Kids: Copper-based Precipitates

Amy Hawthorne

by Amy Hawthorne

4th November 2014

You may have come across Part 1 in our series of chemical reactions that kids can enjoy, and hopefully your children have tried out the simple experiment showing the production of heat and gas.

Today’s experiment to help get children safely learning about – and enjoying – chemistry is all about copper-based precipitates you can find on everyday objects.

Experiment 2: Green Pennies and Copper Plated Nails

A chemical reaction can happen with anything; ions, single elements or compounds. You can even see chemical reactions through visual processes such as a colour change or formation of a precipitate.

In today’s two-step chemical reactions for kids, we will examine the precipitates that form on pennies and nails, giving them that old, dirty colour.

Pennies get dirty over time as the copper slowly reacts with air and forms various copper compounds, giving it that greenish or blackish colour. In the first step, the salt and vinegar solution can dissolve this copper oxide, leaving behind shiny new pennies. It’s possible to replace vinegar with other acidic solutions, such as lemon juice.


The dullness you see on old pennies is caused by a variety of copper-based precipitates


  • Dirty pennies
  • Old iron nails
  • ¼ cup vinegar (acetic acid)
  • 1 teaspoon of salt (sodium chloride)
  • Glass or plastic container
  • Paper towel
  • Water

Method 1

  1. Mix the salt and vinegar in a bowl, and ensure the salt is completely dissolved.
  2. Dip some pennies in this solution and wait a few minutes. Take half the pennies out and simply place them on a paper towel to dry naturally.
  3. Rinse the other half thoroughly in water and allow them to dry.
  4. Come back to your experiment in a few hours to see the difference. If you can’t see any difference, try leaving the pennies in the solution for longer.

You’ll see that leaving the residue of salt and vinegar has turned those pennies dull again very fast. The ones that you rinsed in water should still be shiny. (They will eventually turn green, but this takes more than just a few hours.)

This dullness is caused by a variety of copper-based precipitates, including copper carbonate (from reaction with air), copper chloride (from reaction with salt) and copper acetate (from reaction with vinegar). You can try using just vinegar or just dissolved salt and see what difference it makes.

Method 2

  1. Very important: Keep the salt and vinegar solution for this part of the experiment.
  2. Place iron nails into the solution.
  3. Leave for a few hours.

Nails should now have a copper plating and if you’re lucky, it may even be covered in bubbles! This is hydrogen gas released from the reaction between the copper acetate dissolved in the solution (from your pennies) and the iron.

If it doesn’t work, repeat step 1 with more pennies.

If you’ve been successful with this experiment, please do send us some photos so we can share them! Also, look out for another instalment of chemical reactions for kids, which will be uploaded next week.

See More from ‘Chemical Reactions for Kids’

Experiment 1: Heat and Release of Gas
Experiment 3: Splitting Water (Electrolysis)
Experiment 4: What Factors Affect a Reaction?


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