Chemical Reaction – Penny Cleaner

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Everything in the universe is made of teeny tiny particles called atoms. Some things are made up of just one kind of atom. A penny is made up entirely of copper atoms. Atoms can join together to make molecules. When penny is exposed to oxygen in the air, the copper atoms of the penny and the oxygen atoms in the air combine, a chemical reaction takes place that make a molecule called copper oxide – that is the dirty stuff that you see on the penny.  This “stuff” is often referred to as “tarnish.” When you soak the pennies in taco sauce, another chemical reaction takes place. Try this experiment to watch this chemical reaction.

You Will Need:

• Dirty Pennies
• Taco Sauce
• Vinegar
• Tomato Paste
• Salt
• Water
• Small Plates
• Masking Tape

Put some tarnished pennies in a small dish and pour taco sauce over them. Let the taco sauce sit for a few minutes and then wash the taco sauce off the pennies. How do the pennies look now? If you look at the ingredients in the taco sauce you will notice that the main ingredients are tomato paste, vinegar and salt. Which ingredient affected the tarnish on the pennies? To find out, you need to test different combinations of the ingredients. First, try to polish the pennies with just tomato paste, just salt and just vinegar. How do the pennies look? Then, try polishing the pennies in different combinations of the ingredients: tomato paste + salt, vinegar + salt and tomato paste + vinegar.  Which combination worked best?

Here are some websites that will give you good directions for this experiment and an explanation of the chemical reaction that creates the tarnish and then takes it away again:

• Exploratorium: Copper Caper
• PBS Kids: Fetch Copper Cleanup

Here are some books that will help you see other chemical reactions that polish tarnish from pennies or silver.

• Google Preview – Science Experiments That Surprise and Delight: Taco Sauce Penny Cleaner (pages 60-63)
• Science Rocks!: Spruce Up Silver (pages 41-42)
• Google Preview -  Science Experiments That Fizz and Bubble: Not Quite the Midas Touch (Pages 20-21)
• Mythbusters Science Fair Book – Can Cola Shine a Penny? (Pages 13-14).

Words to Know:

Chemical Reaction – A change in which a substance (or substances) is changed into one or more new substances.

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