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Amber cleans a copper coin with salt and vinegar

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With a 1/4 cup white vinegar and 1 teaspoon salt, you can transform dirty copper pennies into bright and shiny coins. In this short demonstration video, young Amber cleans copper coins with 3 teaspoons of ordinary table salt in half a glass of vinegar.

coin in salt and vinegar
What’s happening here? From this American Chemical Society pdf:

“Pennies are copper-plated zinc coins, with about 2.5% of copper (Cu) per coin. It is the Cu that gives the reddish color to the penny…

“Most pennies that have been around for a while have dark spots of a compound called copper oxide. Copper oxide forms when the copper is oxidized by its reaction with oxygen in the air. Copper oxide dissolves in water, but it usually takes a long time.

“The combination of vinegar (a weak solution of acetic acid), and table salt (sodium chloride) helps to dissolve the copper oxide, and also forms the blue copper(II) ion, which is soluble in water. The penny becomes shiny again!”

the coin exposed to salt and vinegar

“Over time, you should observe that the pennies that were in the vinegar solutions reacted with oxygen in the air and formed a blue-green copper oxide compound, which is the same substance that we see on old copper statues and copper roofs.”

Watch this next: How are coins made at The Royal Mint?

Then watch more copper videos and these science activities:
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How to write invisible ink messages
Ten easy science experiments for kids at home
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• Microwave cupcakes in a mug, an easy chemistry experiment

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