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Chemistry for kids - clean copper pennies

Activity

Clean up your copper pennies (or any copper object)

We recently came across a two-inch souvenir copper penny we bought a long time ago, and found it had tarnished badly. We'd been successful before in soaking old pennies in cola to restore their shine. The tarnish is a coating of copper that has combined with the oxygen in the air. The phosphoric acid in the cola bonds with the copper to remove the coating. But the Coke just didn't do it for us this time - too much tarnish.

These web sites suggest that acid + salt make a more powerful remover:

http://www.cruftbox.com/cruft/docs/cleaningcopper.html
http://pbskids.org/zoom/activities/sci/polishingpennies.htm

So we soaked the big penny in a bowl of lemon juice mixed with a big spoonful of salt. This is a much more interesting experiment than the cola version, because you can see bubbles released and the color of the lemon juice darkening as the chemical reaction proceeds. The cola's color and fizz make all that invisible. But even left soaking overnight, the penny wasn't new and shiny again.

So this morning we tried hot sauce - the main ingredients are vinegar and salt. Wow did it work - we could see the penny brighten before our eyes.

Cautions: If you try this experiment, make sure to protect your skin and eyes - those hot peppers can pack a nasty sting. Also, the penny's surface is a little pitted now - but we're not sure if it was already like that or if the cleaning did it. We don't recommend experimenting on anything valuable.

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