Many have heard of this experiment or seen it on videos but here is how you can do it in on your own without the highly caustic 30% hydrogen peroxide.
Materials:
• Empty water bottle
• 3% hydrogen peroxide (1/2 cup)
• Dish Soap (approximately 1 Tablespoon)
• Dry yeast (1 packet – 2 teaspoons)
• Warm water (6 Tablespoons – 1/3 cup)
• Glass to mix yeast solution
• Spoon to stir yeast solution
• Measuring cups
• Tablespoon
• Teaspoon
• Tray or container for water bottle to sit in
• Food Coloring (optional)
CAUTION: Hydrogen peroxide (even 3%) can be dangerous. Adult supervision is necessary. The foam that forms is not toothpaste and should not be used for that purpose. The resulting solution is safe to touch if you use yeast as the catalyst (however the food coloring may stain you, your clothes, table, etc.). Often potassium iodide gets used for this reaction and if that catalyst is used, the resulting foam will stain your skin.
Experiment:
Pour the warm water from the faucet into the glass and add the dry yeast. Stir the solution with the spoon. This solution should set for about 5 minutes while you add the hydrogen peroxide to the water bottle along with the dish soap. Add food coloring at this point if desired. Swirl the bottle to mix the ingredients. Once the yeast solution has sat for 5 minutes, pour the yeast into the water bottle and watch what happens.
What’s happening?
Hydrogen peroxide has the chemical formula H2O2. This is very similar to the much more stable water molecule, H2O. The hydrogen peroxide has an extra oxygen atom that makes it fairly unstable. The warm water will activate the yeast which has an enzyme in it called catalase that catalyzes (speeds up) the decomposition of H2O2 into H2O and O2. The oxygen molecule that is released is a gas and the gas gets caught up in the soap and causes bubbles to form. The faster the reaction, the faster the bubbles will form and the greater the foaming of the “toothpaste”. You may have noticed some steam being released. This is due to the heat that is generated when the hydrogen peroxide decomposes.
Extension:
Normally when you see this demonstration done it is performed with much higher concentrations of hydrogen peroxide (30%). This is highly caustic and will burn your skin if you get it on you. You can dilute your 3% peroxide to see how this would affect the reaction. You can add more or less yeast as well. The size of the opening on the container will affect how high the bubbles shoot out. If you go with a smaller opening you will want to do this experiment outside so that the soap won’t spray (and stain) your ceiling (see https://www.youtube.com/watch?v=Kou7ur5xt_4)
References
https://www.thoughtco.com/kid-friendly-elephant-toothpaste-demo-604164
https://www.youtube.com/watch?v=j2m7odcvqMA
To view past “ChemShorts for Kids” activities, go to:
https://chicagoacs.org/ChemShorts.
