Hydrogen Peroxide and Yeast Chemical Reaction: A Simple Guide

If you mix hydrogen peroxide with yeast, the yeast acts as a catalyst to speed up the decomposition of hydrogen peroxide into water and oxygen gas. This is a common and safe classroom demonstration of a catalyzed chemical reaction. The hydrogen peroxide and yeast chemical reaction produces a fast-forming foam of oxygen bubbles, which is simply soapy water trapping the released gas.

What Happens During the Reaction

The reaction is a decomposition, meaning one chemical breaks down into simpler substances. Hydrogen peroxide (H₂O₂) naturally breaks down into water (H₂O) and oxygen gas (O₂), but the process is very slow. Yeast contains an enzyme called catalase, which speeds up this decomposition dramatically without being consumed itself.

When you add yeast to hydrogen peroxide, the catalase in the yeast grabs onto the hydrogen peroxide molecules and helps them split apart. The reaction happens almost instantly, releasing a large volume of oxygen gas. If you add a little dish soap to the hydrogen peroxide beforehand, the oxygen bubbles get trapped in the soap, creating a thick, expanding foam. This is often called “elephant toothpaste” because of the way it pushes out of the container.

The chemical equation for the reaction is:

2 H₂O₂ → 2 H₂O + O₂

The yeast (catalase) is written above the arrow to show it is a catalyst, not a reactant that gets used up.

Why the Reaction Works So Fast

The Role of Catalase

Catalase is a biological enzyme found in nearly all living organisms, including humans. Its job is to break down hydrogen peroxide, which is a harmful byproduct of metabolism, into harmless water and oxygen American Chemical Society. A single catalase enzyme can process millions of hydrogen peroxide molecules per second. This makes it one of the most efficient enzymes known.

The Role of Concentration

The speed and intensity of the reaction depend heavily on the concentration of the hydrogen peroxide. Household hydrogen peroxide is typically a 3% solution in water. At this concentration, the reaction with yeast is vigorous but manageable, producing a warm foam that rises quickly. Higher concentrations, like 6% or 12%, produce a much more dramatic and hotter reaction. Concentrations above 30% are dangerous and should never be used for home experiments, as they can cause chemical burns and can decompose explosively when heated Wikipedia.

The Role of Temperature

The reaction rate is also affected by temperature. Warm water (around 30-40°C or 86-104°F) activates the yeast and catalase, making the reaction faster. Cold water slows the reaction down. Boiling water will denature (destroy) the catalase enzyme, stopping the reaction completely.

A Simple Experiment You Can Try

This experiment is safe to do at home with adult supervision, using common household materials.

What you need:

• A clean 16-ounce (500 ml) plastic soda bottle
• 1/2 cup (120 ml) of 3% hydrogen peroxide (from a pharmacy)
• 1 tablespoon (15 ml) of dish soap
• 1 packet of dry active yeast
• 3 tablespoons (45 ml) of warm water
• A funnel
• A shallow pan or tray to catch the foam

Steps:

1. Use the funnel to pour the hydrogen peroxide into the bottle.
2. Add the dish soap and gently swirl the bottle to mix.
3. In a separate small cup, stir the yeast into the warm water. Let it sit for about 30 seconds to activate.
4. Pour the yeast mixture into the bottle and step back.

A thick, warm foam will quickly rise out of the top of the bottle. The foam is non-toxic and can be cleaned up with water. The bottle will feel warm to the touch because the reaction releases energy as heat.

Safety and Practical Considerations

Standard 3% hydrogen peroxide is safe for household use, but it can irritate skin and eyes. Wear safety glasses or goggles to protect your eyes from splashes. If you get hydrogen peroxide in your eyes, flush them with plenty of water for several minutes American Academy of Ophthalmology. Avoid contact with clothing, as it can act as a bleach.

The foam produced is mostly water, soap, and oxygen. It is non-toxic and can be rinsed down the drain with water. The leftover liquid in the bottle is mostly water and inactive yeast. You can pour it down the drain as well.

While the reaction produces water and oxygen, the leftover mixture contains unconverted hydrogen peroxide and soap. Never drink the foam or the liquid left in the bottle.

Key Takeaways

• The reaction is a decomposition of hydrogen peroxide into water and oxygen, catalyzed by the enzyme catalase in yeast.
• Household 3% hydrogen peroxide is safe for this experiment; higher concentrations require professional handling.
• The reaction produces heat and a large volume of oxygen foam when dish soap is added.
• Catalase is a highly efficient enzyme that makes the reaction happen almost instantly.
• Always wear eye protection and avoid contact with skin when handling hydrogen peroxide.