What you need:
• Paper towels
What you do:
• Fold a paper towel into fourths.
• Put the towel in the bowl.
• Slowly pour vinegar into the bowl until the paper towel is completely soaked. (There shouldn’t be a puddle of extra vinegar sitting on top of the paper towel.)
• Put pennies on top of the wet paper towel.
• Wait overnight and observe.
Explanation: The main ingredient in pennies is a metal called copper.It’s copper that gives pennies their reddish-brown color. Vinegar contains a chemical called acetic acid. When acetic acid touches copper, something new is created – a green-blue chemical called carbon acetate. In science, we call this kind of change a chemical reaction. The chemicals in the vinegar and in the copper react (change) when they are combined, making carbon acetate on the pennies.
The tops of the pennies changed color, but not the bottom. That’s because this chemical reaction can only happen if oxygen from the air around us is available. The tops of the pennies are exposed to the air and so oxygen is available to be part of the chemical reaction. The bottoms of the pennies don’t change because they don’t have enough oxygen next to them to make the reaction possible.