This is an easy and fun experiment that doesn’t require any special equipment. Just collect some dirty pennies and get your kids to drop them into a bowl of vinegar with about a teaspoon of salt in it. Watch them go from dull to shiny in seconds! Visit Exploratorium and scroll down to the blue box at the bottom of the page to help you explain to your kids why this experiment works.
Next, take the pennies out of the vinegar. Rinse some of them off, and leave others un-rinsed. Lay them out to dry and come back in about an hour. Are the un-rinsed pennies starting to turn green?
Try this experiment with different types of acidic solutions. Lemon juice, orange juice, and ketchup are all good choices – let your kids think up some others! Do any of these work as well as the vinegar and salt solution?