What you need:
- 125 ml 6% hydrogen peroxide (also labelled 20Vol), available from pharmacies
- 1 sachet dry yeast powder
- lukewarm water
- dishwashing detergent
- food colouring (not cochineal)
- empty soft drink bottle
- plastic tray or tub
- dishwashing gloves
- safety glasses
What to do:
- Empty a full sachet of dry yeast into a cup.
- Add four tablespoons of water and stir until mixed.
- Use a funnel to pour the hydrogen peroxide into the empty soft drink bottle.
- Add a large squirt of dishwashing liquid. Swirl to mix the detergent into the hydrogen peroxide.
- Add ten or fifteen drops of food colouring and swirl the bottle to mix the food colouring into the solution.
- Use the funnel to pour the yeast mixture into the bottle. Do this over the tray or tub as it’s messy.
- The foamy “toothpaste” should rush up out of the bottle.
Be sure to wear gloves and safety eyewear while handling the hydrogen peroxide. Don’t eat the ingredients or the “toothpaste”.
Yeast produces catalase which causes the hydrogen peroxide to break down into liquid water and oxygen gas. The oxygen then makes bubbles in the detergent which foam up out of the bottle. Catalase is a catalyst in the reaction: it makes the reaction go faster but isn’t used up.