Taco Sauce Penny Cleaner

Test your scientific inquiry as you learn about the cleaning power of kitchen chemistry

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It’s one of those things you hear about but wonder if it’s true. Can you use taco sauce to clean the tarnish off of a penny? Believe it or not, taco sauce does a great job of cleaning pennies, but how does it work? Which ingredients in the taco sauce really do the cleaning? Eight year old Jack Spangler tackled these questions as part of his science fair project and made a surprising discovery.


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Here's What You'll Need

  • Dirty pennies (try to collect tarnished pennies that all look the same)
  • Taco sauce
  • Vinegar
  • Tomato paste
  • Salt
  • Water
  • Small plates
  • Masking tape or sticky note

Let's Try It

  1. Let’s start with the hypothesis of this experiment: Taco sauce is a great penny cleaner. If this is true, then we can use the scientific method to determine the science behind this saucy secret.

  2. Place several tarnished pennies on a plate and cover them with taco sauce. Use your fingers to smear the taco sauce all over the top surfaces of the pennies. Remember to wash your hands . . . and don’t lick your fingers because dirty pennies are gross.

  3. Allow the taco sauce to sit on the pennies for at least 2 minutes.

  4. Rinse the pennies in the sink and look at the difference between the top sides of the pennies that touched the taco sauce and the bottom sides. It’s no myth—taco sauce does the trick.

  5. For an easy-to-see comparison, use another tarnished penny and cover only half of the surface of the penny with taco sauce. Don’t smear the sauce around with your finger this time—you want a nice dividing line between the two sides. Let the penny and sauce
    combo sit for a few minutes and rinse. It’s a cool half-and-half penny.

  6. Since the hypothesis is true, which of the ingredients in taco sauce is responsible for its cleaning power? Let’s find out . . .
    The list of ingredients on the packet of taco sauce reveals four substances to test: vinegar, tomato paste, salt, and water.

  7. Place two equally tarnished pennies on each of four different plates. Use masking tape or a sticky note to mark each plate with the taco sauce ingredient you are testing (vinegar, tomato paste, salt, or water).

  8. Cover the pennies with the various ingredients, smear them around with your fingers, and allow the pennies to sit for at least 2 minutes. Be sure to wash your hands.

  9. Rinse the pennies from each test plate with water. Which ingredient cleaned the pennies the best?

  10. None of the individual ingredients do a good job of cleaning the dirty pennies. In fact, the results are less than impressive. Maybe two or more of the ingredients work together to react against the copper oxide (the tarnish) on the penny. Let’s find out . . .
    Place two equally tarnished pennies on each of three different plates. Make three signs that say “Tomato Paste + Vinegar,” “Salt + Vinegar,” and “Tomato Paste + Salt.”

  11. Cover the pennies with each of the mixtures, smear them around with your fingers, and give the ingredients at least 2 minutes to react. Wash your hands.

  12. Rinse the pennies under water. Now what do you notice?

  13. And the winner is . . . VINEGAR + SALT! But why?

How Does It Work

The clear winner is the mixture of vinegar and salt. Neither vinegar nor salt by itself cleaned the pennies, but when they were mixed together something happened. The chemistry behind the reaction is somewhat complicated but very interesting. When the salt and the vinegar are mixed together, the salt dissolves in the vinegar solution and breaks down into sodium and chloride ions. The chloride ions then combine with the copper in the penny to remove the tarnish or copper oxide from the surface of the penny. It is also well known that a mixture of lemon juice and salt does a good job of removing tarnish from metals and works very well on pennies. By themselves, the salt and vinegar do very little in the way of removing the coating of copper oxide on the penny, but together these ingredients make a great cleaning agent.

So, the secret in taco sauce is the combination of the ingredients. Someone might argue that tomato paste is slightly acidic and may contribute in a small way to removing the copper oxide coating, but the real “power ingredients” are salt and vinegar.

Science Fair Connection

The “Taco Sauce Penny Cleaner” is a great example of a science fair project. First, you ask a question—does taco sauce really clean pennies? You find that it does and then you ask another question—what is it in the taco sauce that causes it to clean pennies? You run multiple tests and isolate one variable at a time to see if the vinegar, the tomato paste, the salt, or the water is the real cleaning agent for the pennies. Guess what? Nothing cleans the penny. Now what do you do? You ask another question—could a combination of ingredients cause the cleaning action? Again, you isolate the variables and eventually reach the conclusion that a combination of vinegar and salt cleans the pennies.

The “Taco Sauce Penny Cleaner” experiment clearly shows scientific inquiry in motion—ask a question, run some tests, ask another question, run some tests, ask another question, run some tests, and eventually come to some conclusions. Good science fair projects should leave you with more questions than they answer. What do you still wonder about? How could you extend the experiment to try to find some more answers? Did this activity cause to you wonder about something else entirely? Could you create a new experiment based on your new questions?

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