Elephant Toothpaste: Catalysts and a Lot of Foam

Set the expectation first, because this is where most families end up disappointed. The volcanoes in the viral videos use 30 to 35 percent hydrogen peroxide, which causes severe chemical burns on contact and has no business in a kitchen. This elephant toothpaste experiment uses the 3 percent brown-bottle peroxide from a pharmacy, and what you get is a column of warm foam that rises 20 to 40 centimetres over about half a minute and fills a baking tray. That is genuinely impressive, it is safe with goggles, and the chemistry it teaches is identical. Everyone wears eye protection, including you.

Key Takeaways

• You’ll decompose 3 percent hydrogen peroxide with yeast, trapping the oxygen as foam with dish soap.
• It teaches catalysis: a catalyst speeds up a reaction without being used up, and this one is among the fastest enzymes known.
• Best for ages 8 to 14. Goggles are required, not suggested, for everyone at the table.
• The usual mistake is water that’s too hot for the yeast, which kills the enzyme and kills the reaction.
• The foam is not a play material afterwards. It holds leftover peroxide, soap and yeast.

What You’ll Need

Item	How much	Where to get it	If you don’t have it
3% hydrogen peroxide, the brown pharmacy bottle	100 mL	Any pharmacy, first-aid aisle	There is no substitute. Do not use 6%, 9% or 12% hair developer, and never 30–35% “food grade” peroxide sold online
Dried active yeast	1 sachet, about 7 g	Baking aisle	Fresh yeast at roughly three times the weight. Baking powder will not work
Warm water, about 40 °C	45 mL, 3 tbsp	Tap	It must be warm, not hot. Above about 55 °C the enzyme stops working
Washing-up liquid	1 tbsp	Kitchen sink	Any liquid soap or shampoo
Food colouring	5–10 drops	Baking aisle	Skip it; it stains and adds nothing chemically
Empty plastic bottle, narrow neck	1, 500 mL	Recycling	Do not use glass. A plastic funnel helps
Deep baking tray or washing-up bowl	1, as big as you have	Kitchen	Do it outside on paving
Safety goggles	1 pair per person	Hardware shop	Do not run this without them
Disposable gloves	1 pair	Kitchen drawer
Measuring jug, tape measure, phone stopwatch	1 each	Kitchen

Nothing here is food, and nothing from this experiment is eaten or tasted.

Time: prep 10 min, experiment 10 min, cleanup 15 min Cost: a bottle of peroxide and a sachet of yeast Mess level: do this outside, or in a sink, in a tray. The foam overflows by design

Do the Experiment: The Elephant Toothpaste Experiment

Step 1 - Goggles on, tray down, bottle in the tray

Everyone at the table puts goggles on before any bottle is opened, adults included, because children copy what they see. Stand the plastic bottle in the middle of the deep tray. If you’re indoors, put the tray in the sink. Decide now where the foam will go.

What you should see: nothing yet. This step exists because peroxide in an eye is a genuine injury and the foam travels further than anyone expects.

Step 2 - Charge the bottle with peroxide and soap

Pour 100 mL of 3 percent hydrogen peroxide into the bottle, using a funnel if you have one. Add one tablespoon of washing-up liquid and a few drops of colouring. Swirl gently, do not shake, and leave the cap off. The cap stays off for the rest of the experiment, permanently.

What you should see: a coloured liquid with no bubbles. If it’s already fizzing gently, that’s a trace of metal or dust catalysing it, which is harmless and a good hint about what’s coming.

Step 3 - Wake the yeast in warm water and wait a full minute

In a cup, stir the whole 7 g sachet of yeast into 45 mL of water at about 40 °C. That is warm to a fingertip, not hot. Stir for 30 seconds until there are no dry lumps, then leave it for a minute. Temperature matters more than anything else in this experiment.

What you should see: a beige, slightly frothy slurry. If the water was hot enough to be uncomfortable on your finger, you may have denatured the catalase and the reaction will be weak or absent. Cool water is slow; hot water is fatal.

Step 4 - Pour the yeast in all at once and step back

Have your child predict the foam height out loud first, and write the number down. Then pour the whole yeast mixture into the bottle in one go and take a step back. Start the stopwatch.

What you should see: a two-to-four-second pause, then foam climbing the neck and erupting. With 3 percent peroxide expect a steady column rising 20 to 40 cm above the bottle over 20 to 60 seconds, then slowing. It keeps producing foam for several minutes afterwards. Touch the outside of the bottle, not the foam: it is noticeably warm, because the reaction releases heat.

Step 5 - Measure the foam and work out the gas

Scrape the foam into a measuring jug and read the volume. Then do the arithmetic with your child: 100 mL of 3 percent peroxide contains about 3 g of hydrogen peroxide, which is 0.088 moles, which decomposes to 0.044 moles of oxygen. At room temperature one mole of gas occupies about 24.5 litres, so complete decomposition releases roughly 1.1 litres of oxygen.

What you should see: a foam volume of several litres, because each bubble is mostly gas with a thin soap film. The measured volume should be in the same ballpark as the calculated gas volume plus the original liquid, and the discrepancy is a good discussion: foam collapses, and not all the peroxide decomposes in the first minute.

What’s Actually Going On

Hydrogen peroxide is unstable. The reaction 2 H₂O₂ → 2 H₂O + O₂ releases energy, which means the bottle in your hand is thermodynamically determined to turn into water and oxygen eventually. The reason a pharmacy bottle lasts months is kinetics: the reaction has a high activation energy, so at room temperature it happens extremely slowly. That is also why peroxide is sold in brown bottles, since light speeds it up.

A catalyst provides a different route with a lower activation energy, so the same reaction runs far faster, and the catalyst comes out of it unchanged. Conklin and Kessinger’s demonstration of catalytic peroxide decomposition in the Journal of Chemical Education in 1996 is the classroom reference for exactly this.

The catalyst in your bottle is catalase, an enzyme that essentially every oxygen-tolerant organism carries because peroxide is a toxic by-product of ordinary metabolism. Catalase is extraordinarily fast. Chelikani, Fita and Loewen’s 2004 review in Cellular and Molecular Life Sciences describes catalases as among the most efficient enzymes known, turning over enormous numbers of peroxide molecules per second per active site. The yeast is simply a convenient bag of catalase, and this is worth being precise about: the yeast is not fermenting anything and is not eating the peroxide. Only one of its enzymes is doing the work.

That also explains the temperature rule in Step 3. Catalase is a protein with a specific folded shape, and that shape is what makes the active site work. Heat it past roughly 55 °C and it unfolds irreversibly, which is denaturation. Dead yeast contains denatured catalase and produces almost nothing, which makes a beautiful control: boil a second sachet, cool it, and run the experiment again with it.

The soap is not a reactant at all. It is a visualiser. Without soap you get a bottle that fizzes, warms up and releases oxygen quietly into the air, and you learn almost nothing from watching it. The soap lowers the liquid’s surface tension so the escaping oxygen gets trapped in thin films instead of bursting at the surface, and each bubble is mostly gas. That is why a litre of oxygen becomes several litres of foam.

Now the honest comparison with the videos. Foam volume scales with the amount of peroxide, and 30 percent peroxide holds ten times as much per millilitre as 3 percent, so the same 100 mL would release around 11 litres of oxygen instead of 1.1. That is the entire difference between your tray and a column that hits the ceiling, and it is why that version is not a home experiment: PubChem’s record lists concentrated hydrogen peroxide as causing severe skin burns and eye damage. The chemistry is identical at either concentration. The injury risk is not.

One more correction, because it’s common: this is not a volcano and it has nothing to do with the baking soda and vinegar reaction. That one is an acid-base reaction producing carbon dioxide, and both reactants are consumed. Here a single compound falls apart and the yeast is unchanged at the end. If you’ve done our vinegar and baking soda chemistry, running both and asking what is different is a better lesson than either alone.

How to Explain It to Your Kid

Ages 5–8: a helper that doesn’t get used up

They should be watching from behind goggles rather than pouring, at this age. The framing: the liquid in the bottle really wants to break into water and air, but it’s slow, like a very lazy change. The yeast is a helper that shows it a shortcut. The helper doesn’t get used up and doesn’t become part of the answer; it just makes it happen fast. Then the soap catches the air so you can see how much there was.

Ages 9–12: catalyst, enzyme and a measured volume

Introduce catalyst and enzyme, and do the Step 5 measurement properly. Then run the yeast-amount series: quarter, half and a full sachet with everything else identical, measuring foam height each time. More catalyst makes it faster but not bigger, because the amount of peroxide sets the total gas. Discovering that distinction, rate versus yield, is the single most valuable idea in the whole experiment.

Ages 13+: activation energy, denaturation and stoichiometry

Give them the full account: a thermodynamically favourable reaction with a kinetic barrier, a catalyst offering a lower-energy path, and an enzyme whose tertiary structure creates the active site and is destroyed by heat. Then the stoichiometry from Step 5, properly written out. The investigation worth running: a temperature series on the yeast water at 20, 30, 40, 50 and 60 °C, measuring time to peak foam. You should see a rise to an optimum and then a collapse, which is the classic enzyme activity curve, measured at home.

The question to ask: “If we doubled the yeast, would we get twice as much foam? What about if we doubled the peroxide? Answer both before we test either.”

Why Teaching This Early Pays Off

Catalysis is one of the most consequential ideas in chemistry and one of the least intuitive. Something that makes a reaction go faster while not being consumed violates a child’s sensible expectation that if something does work, it gets used up. Catalytic converters, enzymes in digestion and essentially all of biochemistry run on the same idea.

The rate-versus-yield distinction is the second payoff and arguably the bigger one. Students routinely confuse “faster” with “more” in chemistry exams, and the yeast series makes the difference physical: more catalyst, same total foam, shorter time.

The teaching structure that works is Predict-Observe-Explain, described by White and Gunstone in Probing Understanding. Ask for the foam-height prediction before the yeast goes in, every time. Alfieri and colleagues’ 2011 meta-analysis is the relevant caution: spectacular demonstrations are exactly the ones children watch without learning from unless an adult is asking questions. One eruption teaches nothing; three eruptions with different yeast amounts and a table of numbers teaches catalysis.

Before You Start: What Parents Should Know

Best age	8 to 14. An adult pours the peroxide; the child can pour the yeast and do all measuring. Below 8, watching from behind goggles is the right role
Supervision	Constant and hands-on from start to finish, including cleanup
Real hazards	Concentration is the whole safety story. Use only 3% hydrogen peroxide, the brown bottle sold for first aid. PubChem’s record for hydrogen peroxide classifies the concentrated substance as causing severe skin burns and eye damage, and the 30–35% grades used in viral videos do precisely that on skin contact. 3% still stings, still temporarily whitens skin, and is a real eye irritant, so goggles for everyone and gloves for whoever pours. Next: never put the cap on the bottle at any point, because the gas has to go somewhere. Use a plastic bottle, never glass. Keep it away from any flame, because the foam is oxygen-enriched and oxygen makes fires burn harder. Finally, the foam is not a play material: it contains unreacted peroxide, soap and yeast, so no hands in it, no handprints on the wall, and hands washed properly before anyone touches their face
Don’t	Don’t substitute a stronger peroxide to make it bigger. Hair developer at 6, 9 or 12 percent and “food grade” 35 percent peroxide sold online are both available and both cause injuries that 3 percent does not. If the 3 percent version looks too small, add a second bottle of 3 percent rather than one bottle of something stronger. Don’t cap it, don’t use glass, and don’t do it near a candle

When It Doesn’t Work

• Almost nothing happened. Nine times out of ten the yeast water was too hot and the catalase is denatured. It needs to be warm to a fingertip, around 40 °C, and never uncomfortable. Remake the yeast with cooler water.
• A slow weak froth instead of a column. Either not enough soap, or old peroxide. Peroxide decomposes slowly in storage, especially once opened, and a bottle that has been in a bathroom cabinet for two years may be mostly water. Buy a fresh bottle; they cost very little.
• Lots of bubbles but no column. Soap problem. One tablespoon in 100 mL is right, swirled in rather than shaken, because pre-foaming the liquid wastes it.
• It erupted sideways and missed the tray. The bottle wasn’t vertical or the neck was too wide. A narrow-necked 500 mL bottle gives a tall column; a wide jar gives a slow spill. And if it went off before you were ready, something metallic or dusty was in the bottle: rinse bottles with clean water first.

Take It Further

Separate rate from yield. Four runs with identical peroxide and soap but a quarter, half, three-quarters and a full sachet of yeast. Measure time to peak and final foam volume for each: time should fall sharply, volume should barely change. This contains the distinction most chemistry students get wrong.

Prove the catalyst survives. After a run, let the foam collapse, pour off the liquid, and add a second 50 mL of fresh 3 percent peroxide to the same bottle without adding more yeast. It goes again, weaker but unmistakably: a catalyst that still works after the reaction is the definition made visible.

Change the catalyst entirely. Try raw liver or raw potato instead of yeast, both rich in catalase, and compare each with its boiled version. The boiled one does almost nothing: denaturation demonstrated with a vegetable, and it connects to the enzyme work in our fermentation science guide.

What to Watch For Over the Next 3 Months

• Week 4: they notice peroxide fizzing on a graze: the same reaction, catalysed by catalase in their own cells.
• Month 2: the word “catalyst” appears in the right sense, often about a car exhaust or enzymes in biology.
• Month 3: worth encouraging: why peroxide exists in our bodies at all if it’s toxic. The answer runs through oxidative metabolism.

Frequently Asked Questions

Can I use stronger peroxide to make it bigger, just once?

No. The 30 to 35 percent grades sold online cause severe skin burns and eye damage on contact, and salon developers at 6 to 12 percent are also well beyond what belongs in a kitchen demonstration. If you want more foam, use more 3 percent peroxide. Two bottles of 3 percent is twice the foam at the same risk level.

Why yeast rather than potassium iodide?

Both are genuine catalysts, but iodide performs best with higher peroxide concentrations, while yeast is a sachet from the baking aisle, makes the enzyme story available and gives you the boiled-yeast control.

Is the foam safe to touch?

Treat it as not for touching. It contains unreacted 3 percent peroxide, soap and yeast, and 3 percent peroxide stings, temporarily whitens skin and irritates eyes. If a child does get it on their hands, rinse with plenty of water and keep hands away from faces. To dispose of it, dilute with lots of water and rinse it down the drain, then wash the tray.

What should we do if peroxide gets in an eye?

Rinse immediately with plenty of clean running water for several minutes, keeping the eye open, and seek medical advice. This is precisely why goggles are listed as required rather than recommended, and why adults wear them too.

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About the author

Ricky Flores is the founder of HiWave Makers and an electrical engineer with 15+ years of experience building consumer technology at Apple, Samsung, and Texas Instruments. He writes about how kids learn to build, think, and create in a tech-saturated world. Read more at hiwavemakers.com.

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Sources

1. National Center for Biotechnology Information. “Hydrogen peroxide, CID 784: GHS classification and physical properties.” PubChem. https://pubchem.ncbi.nlm.nih.gov/compound/784
2. Conklin, A. R., & Kessinger, A. (1996). “Demonstration of the catalytic decomposition of hydrogen peroxide.” Journal of Chemical Education, 73(9), 838. https://doi.org/10.1021/ed073p838
3. Chelikani, P., Fita, I., & Loewen, P. C. (2004). “Diversity of structures and properties among catalases.” Cellular and Molecular Life Sciences, 61(2), 192–208. https://doi.org/10.1007/s00018-003-3206-5
4. White, R. T., & Gunstone, R. F. (1992). Probing Understanding. Falmer Press, London.
5. Alfieri, L., Brooks, P. J., Aldrich, N. J., & Tenenbaum, H. R. (2011). “Does discovery-based instruction enhance learning?” Journal of Educational Psychology, 103(1), 1–18. https://doi.org/10.1037/a0021017
6. National Research Council. (2012). A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas. National Academies Press. https://doi.org/10.17226/13165