Here is a chemical reaction that is easy and fun to do – cleaning pennies with vinegar and salt! All you need are some dull, dirty pennies, salt, and vinegar. We put our pennies on a paper plate to work with them.
I asked the boys to try cleaning their pennies with soap and water first. They scrubbed, but were not able to get the pennies any cleaner! I explained that pennies get their dull color when the copper in them reacts with oxygen in the air to form copper oxide. Sometimes, pennies even get a greenish hue from the copper oxide.
Since the copper oxidizing is a chemical change and not a physical change (like simply getting dirt on something), soap will not wash it off. It takes a chemical reaction! The acetic acid in the vinegar reacts with the copper oxide and dissolves it.
The boys were impressed with the results!