ChemixaLEARN CHEMISTRY

Elephant toothpaste, small and safe

Objective: decompose hydrogen peroxide with a yeast catalyst and trap the released oxygen in soap foam. You will use only small amounts of household 3% peroxide, observe the rate change the catalyst causes, and explain the reaction equation.

Safety:

Use ONLY household 3% hydrogen peroxide and small quantities; never use stronger peroxide. An adult must supervise the entire activity. Wear safety glasses; keep the foam away from eyes and do not touch your face. The foam is warm, so let it cool before handling.

Materials

  • Small plastic bottle (250 mL or less)
  • 3% hydrogen peroxide (household brown bottle)
  • Dish soap
  • Packet of active dry yeast
  • Warm water
  • Small cup
  • Tray to catch overflow
  • Safety glasses

Procedure

1

Measure the peroxide

Stand the small bottle on a tray and pour in about 60 mL of 3% hydrogen peroxide.

2

Add soap

Add a squirt of dish soap and swirl gently to mix.

3

Activate the yeast

In a separate cup, stir one packet of yeast into two tablespoons of warm water until mostly dissolved.

4

Add the catalyst

Pour the yeast mixture into the bottle and step back.

5

Observe and feel

Watch the foam rise, note how fast it starts, and carefully feel the warmth of the bottle from the side.

6

Clean up

Once finished, rinse everything down the drain with plenty of water.

What to observe

  • Foam begins rising within seconds of adding the yeast mixture.

  • The foam column is warm to the touch.

  • No foam forms in a control bottle without yeast.

  • The reaction slows and stops as the peroxide is used up.

Why it happens

Hydrogen peroxide naturally decomposes into water and oxygen gas, but very slowly: 2H2O2 -> 2H2O + O2. Yeast contains an enzyme called catalase that speeds this reaction enormously without being used up, which is the definition of a catalyst. The oxygen gas gets trapped by the dish soap into thousands of bubbles, producing the foam column. The reaction also releases heat, so the foam feels warm. Because you use small amounts of household 3% peroxide, the reaction is vigorous but manageable; the large-scale version with concentrated peroxide is dangerous and must never be attempted at home.

Try variations

  • Run a control with no yeast to prove the catalyst matters.

  • Try warm versus cool peroxide and compare foam speed.

  • Add food coloring before the yeast for a striped foam column.