Elephant toothpaste
01 // Question
How does the amount of yeast added change how fast and how high the foam rises?
Yeast contains catalase, an enzyme that speeds up hydrogen peroxide breaking apart without being used up itself.
02 // Variables
Independent
Amount of yeast added- 1 teaspoon
- 2 teaspoons
- 3 teaspoons
Dependent
Foam height and reaction speed- Peak foam height and mean/range across three trials, cm
- Observed plateau time across three trials, seconds at 10-second checks
03 // Hypothesis
IF the amount of yeast added to the hydrogen peroxide mixture increases, THEN foam may rise sooner or reach a greater height, up to a point, BECAUSE a larger amount of yeast supplies more catalase, while bubble size and foam drainage also affect the measured height.
04 // Procedure
1. Measure the base
For each of nine runs, add 120 mL of 3% household hydrogen peroxide and 60 mL dish soap to the same open 600 mL bottle. Set it in a tray; food coloring is optional.
2. Prepare one yeast amount
For each fresh run, stir its labeled 1, 2, or 3 teaspoon yeast portion into exactly 60 mL warm, not hot, water. Keep water volume and temperature the same; change only yeast amount.
3. Add yeast and time
Pour the yeast mixture into the bottle and start timing at once. Keep the bottle open and stand back as foam rises.
4. Record the foam
Record height every 10 seconds until it is unchanged or lower at two consecutive checks. Keep the raw readings, greatest height, and observed plateau time for each run.
5. Repeat each amount
Run three fresh trials at 1 teaspoon, three at 2 teaspoons, and three at 3 teaspoons. Rinse and fully dry the bottle between runs; calculate each condition's mean and range.
Materials // Prepare the bench
- 3% hydrogen peroxide
- active dry yeast
- warm water
- dish soap
- narrow plastic bottle
- tray
- measuring cup
- spoon
- goggles
- gloves
05 // Data table
| Yeast | Peak height · trials 1 / 2 / 3 (cm) | Mean peak (cm) | Range (cm) | Plateau time · trials 1 / 2 / 3 (s) | Mean time (s) |
|---|---|---|---|---|---|
| 1 teaspoon | ____ / ____ / ____ | ____ | ____ | ____ / ____ / ____ | ____ |
| 2 teaspoons | ____ / ____ / ____ | ____ | ____ | ____ / ____ / ____ | ____ |
| 3 teaspoons | ____ / ____ / ____ | ____ | ____ | ____ / ____ / ____ | ____ |
Formula 2 H2O2 → 2 H2O + O2 (catalase speeds up this decomposition without being consumed)
06 // What to expect
Compare the three trials at each yeast amount using their mean peak height, range, and mean observed plateau time. More yeast may make foam rise sooner or reach a greater height, but the foam column is only a proxy: bubble size and drainage affect height too. The pattern can level off when another ingredient limits the reaction, so do not assume a fixed result.
The reaction releases heat as hydrogen peroxide decomposes, so the bottle or foam may feel warm. Keep it on a tray and do not touch or taste the foam.
07 // Lab notes
- Use only 3% hydrogen peroxide — the kind sold as a household antiseptic, not a stronger lab or salon-grade solution.
- Wear goggles and do this over a tray; the foam is warm and can overflow quickly once the reaction starts.
08 // Remember
A catalyst doesn't get used up. It just makes a reaction that was always going to happen go faster.
09 // What the foam does and does not measure
Hydrogen peroxide breaks down into water and oxygen. Yeast contains catalase, which speeds that reaction, and soap traps some of the released oxygen in bubbles. The foam column is therefore a visible sign that gas is being produced and captured. Its height is not a direct measurement of the oxygen volume: bubble size, soap amount, bottle shape, and how quickly foam drains all change the column.
For a fair test, pick one variable such as yeast amount, yeast-water temperature, or peroxide volume. Keep the bottle, peroxide concentration, soap volume, mixing order, and observation time the same. Use a tray under the bottle and mark a ruler beside it if comparing foam height. Run a no-yeast control if the lesson is about the catalyst; it shows what happens to the same peroxide mixture without the added yeast.
10 // Read the reaction as a timed process
Start the timer at the same event in every trial, such as when the yeast mixture enters the bottle. Record foam height at regular intervals instead of only writing the maximum. A time series can show whether one condition produces foam faster, reaches a higher peak, or collapses sooner. Those are different outcomes. For example, a tall early peak followed by rapid drainage is not the same result as a shorter foam that remains stable.
Warm water can increase yeast activity over a moderate range, but very hot water can damage yeast proteins and reduce activity. The expected pattern is not 'hotter always makes more foam.' If temperature is the variable, use measured water temperatures and avoid hot-water handling by students unless teacher procedures allow it. Use only standard 3% peroxide for this classroom version; concentrated peroxide can cause serious injury and is not an appropriate substitution.
11 // Safety, cleanup, and useful follow-up
Wear goggles, keep the bottle on a tray, and do not seal the reaction vessel. Gas must be able to escape; a sealed bottle can build pressure. Keep the foam away from eyes and mouths, and wash hands after cleanup. If peroxide contacts skin or eyes, follow the product label and school safety procedure. The familiar nickname does not mean the foam is toothpaste or safe to ingest.
If a trial makes little foam, check that the yeast was active, the peroxide was fresh, and the yeast mixture was not too hot. Confirm that the same amount of soap was added and the timer started consistently. For a stronger follow-up, measure oxygen with teacher-approved gas collection apparatus or compare mass before and after in an open setup; explain how escaping gas affects the measurement. Do not infer reaction rate from foam height alone without naming the foam-stability limits.
12 // Distinguish reaction speed from foam stability
A taller foam column can result from faster oxygen production, smaller bubbles, or foam that drains more slowly. Foam height is a useful classroom proxy, not a direct measurement of oxygen volume or reaction rate. Record height at the same fixed times in every trial and note when the column begins to collapse. If temperature is the tested factor, measure the yeast-water mixture before combining it with peroxide, while keeping the other amounts and mixing steps constant.
Use only the dilute classroom procedure and keep the bottle open to the air. Concentrated peroxide is not a safe upgrade. Place the setup in a tray, wear splash goggles, and have an adult manage cleanup and disposal. The nickname is playful; the foam is not toothpaste and must never be touched to the mouth or tasted.
13 // Make the yeast comparison repeatable
Prepare a fresh yeast mixture for each run, using the assigned yeast amount in the same 60 mL of warm water at the same measured temperature. Measure the same peroxide and soap amounts into the same bottle, and start the timer as the yeast mixture enters it. Record every 10-second height reading until the height is unchanged or lower at two consecutive checks; this makes the peak and observed plateau rule repeatable.
Run three fresh trials at each yeast amount. Record every peak height and plateau time, calculate mean and range for each outcome, and keep individual readings visible so an unusual run does not hide the spread. Rinse and fully dry the bottle between runs. Change only yeast amount in this investigation; test temperature or peroxide concentration in a separate comparison.
14 // Questions people ask
Is elephant toothpaste dangerous?
The classroom version made with 3% hydrogen peroxide is low risk with goggles and gloves, but it does get warm and can overflow fast, so keep it on a tray. A stronger, lab-grade version made with 30% hydrogen peroxide is significantly more hazardous and is a demonstration for trained adults, not a student experiment.
What is the catalyst in the elephant toothpaste experiment?
The catalase enzyme in yeast is the catalyst. It speeds up the breakdown of hydrogen peroxide into water and oxygen gas without being consumed itself, which is why a small amount of yeast can process a large volume of peroxide.
Why does the bottle feel warm afterward?
The decomposition of hydrogen peroxide into water and oxygen releases energy as heat, making this an exothermic reaction. Do not touch the foam; use that warmth only as an observation.
Why run three trials for each yeast amount?
Foam height and stopping time vary with yeast freshness, bubbles, drainage, and small timing differences. Keep all three readings, then compare each amount's mean and range instead of drawing a conclusion from one run.
15 // Keep going
Can you explain the investigation?
Elephant toothpaste · Student Data Sheet
Question: How does the amount of yeast added change how fast and how high the foam rises?
Hypothesis: If the amount of yeast added to the hydrogen peroxide mixture increases, then foam may rise sooner or reach a greater height, up to a point, because a larger amount of yeast supplies more catalase, while bubble size and foam drainage also affect the measured height.
Materials
- 3% hydrogen peroxide
- active dry yeast
- warm water
- dish soap
- narrow plastic bottle
- tray
- measuring cup
- spoon
- goggles
- gloves
Safety before starting
- Use only 3% household hydrogen peroxide, splash goggles, a tray, and adult supervision. Never substitute concentrated peroxide; keep the solution and foam out of eyes and mouths.
- Do not seal the reaction bottle. The foam may feel warm; let the adult manage the setup and cleanup, then wash hands.
Lab notes
- Use only 3% hydrogen peroxide — the kind sold as a household antiseptic, not a stronger lab or salon-grade solution.
- Wear goggles and do this over a tray; the foam is warm and can overflow quickly once the reaction starts.
Variables
Independent: Amount of yeast added · Dependent: Foam height and reaction speed
Keep constant: 120 mL of 3% hydrogen peroxide · 60 mL dish soap · same open 600 mL bottle · 60 mL yeast water at the same temperature · three fresh runs per yeast amount
Procedure
- Measure the base: For each of nine runs, add 120 mL of 3% household hydrogen peroxide and 60 mL dish soap to the same open 600 mL bottle. Set it in a tray; food coloring is optional.
- Prepare one yeast amount: For each fresh run, stir its labeled 1, 2, or 3 teaspoon yeast portion into exactly 60 mL warm, not hot, water. Keep water volume and temperature the same; change only yeast amount.
- Add yeast and time: Pour the yeast mixture into the bottle and start timing at once. Keep the bottle open and stand back as foam rises.
- Record the foam: Record height every 10 seconds until it is unchanged or lower at two consecutive checks. Keep the raw readings, greatest height, and observed plateau time for each run.
- Repeat each amount: Run three fresh trials at 1 teaspoon, three at 2 teaspoons, and three at 3 teaspoons. Rinse and fully dry the bottle between runs; calculate each condition's mean and range.
Record your observations
| Yeast | Peak height · trials 1 / 2 / 3 (cm) | Mean peak (cm) | Range (cm) | Plateau time · trials 1 / 2 / 3 (s) | Mean time (s) |
|---|---|---|---|---|---|
Formula: 2 H2O2 → 2 H2O + O2 (catalase speeds up this decomposition without being consumed)
Answer key and expected pattern
Compare the three trials at each yeast amount using their mean peak height, range, and mean observed plateau time. More yeast may make foam rise sooner or reach a greater height, but the foam column is only a proxy: bubble size and drainage affect height too. The pattern can level off when another ingredient limits the reaction, so do not assume a fixed result.
The reaction releases heat as hydrogen peroxide decomposes, so the bottle or foam may feel warm. Keep it on a tray and do not touch or taste the foam.
Remember: A catalyst doesn't get used up. It just makes a reaction that was always going to happen go faster.