What You Need:
- Bar of Ivory soap (available at any superstore)
- Various bars of another brand of soap
- Deep bowl of water
- Paper towel
- Microwave oven
- Ask a parent or adult to help you with this experiment
- Fill the bowl with water.
- Drop the bars of soap in the bowl of water. Notice how all of the bars of soap sink except for the Ivory brand soap.
- Remove the Ivory soap from the water and break it in half to see if there are any pockets of air hiding in the middle of the bar. But there are no pockets of air, so how does the soap float?
- ¸Place the bar of Ivory soap in the centre of a paper towel and place the whole thing in the centre of the microwave oven.
- Cook the bar of soap for 2 minutes. Don't take your eyes off the bar of soap as it begins to expand and erupt into beautiful puffy clouds.
- Allow the soap to cool for a minute or so before touching it.
- The soap will be puffy but rigid.
Ivory soap is one of the few brands of bar soap that floats in water. Ivory soap floats because it has air pumped into it during the manufacturing process. When you place this soap in the microwave, it actually starts to pop like a marshmallow. The air bubbles in the soap contain water. When the water is heated in the microwave, it vaporises and forms bubbles and the heat causes trapped air to expand. This effect is actually a demonstration of Charles' Law. Charles' Law states that as the temperature of a gas increases, so does its volume. When the soap is heated, the molecules of air in the soap move quickly, causing them to move far away from each other. This causes the soap to puff up and expand to an enormous size. This is the only brand of soap that will form rigid soap suds, while the others simply melt in the microwave.