About the chemical reaction
The yeast in this demonstration acts as a catalyst (a helper). It speeds up the chemical reaction – the breaking down of the hydrogen peroxide into water and oxygen. The hydrogen locks onto the yeast and the yeast split it into water and oxygen, without being chemically changed itself. The oxygen produced combines with the dishwashing liquid to create the foam. So each of those little bubbles is filled with oxygen. Because this is an “exothermic reaction” (heat producing), it turns some of the water into steam. When you run your hands through the foam, you can feel the heat created! The foam produced is just water, soap, and oxygen so you can clean it up with a sponge or allow it to soak into the grass. This experiment is often called “Elephant’s Toothpaste” because it looks like toothpaste coming out of a tube.
If you want to take this a step further and turn the demonstration into an experiment, you could ask some questions such as:
- What happens if you add the dry yeast without mixing it with water?
- Does the amount of yeast you add affect the amount of foam produced?
- How does the size of the bottle affect the amount of foam produced?
- What happens if you change the amount of hydrogen peroxide?
You will need:
- An empty plastic bottle
- 120 ml Hydrogen Peroxide (between 3 & 6 percent concentration – no more than that)
- Dishwashing Liquid
- Food Colouring
- Dry Yeast
- Hot Water
- Stand the bottle on a tray (or out on the grass in the garden).
- Using the funnel, pour the hydrogen peroxide into the bottle & add a few drops of food colouring & dishwashing liquid.
- Mix the yeast with hot (but not boiling) water in a bowl.
- Using the funnel pour the yeast mixture into the bottle & quickly stand back!
- The liquid will start bubbling before producing a foam that will spurt from the neck of the bottle.