EXPERIMENT 5.2.1

PURPOSE:

To observe an exothermic reaction that produces a large amount of foam, and understand the role of catalysts in chemical reactions.

MATERIALS:

• 250 mL flask
• 75 mL 30% hydrogen peroxide
• 2 tablespoons dishwashing soap
• Food coloring (your choice of color)
• 1 packet of active dry yeast
• Warm water
• Measuring cup
• Sink or outdoor area (for mess containment)
• Safety goggles

BACKGROUND INFORMATION:

Elephant Toothpaste is a fun demonstration of an exothermic reaction (one that releases heat) and catalysis. In this experiment, hydrogen peroxide (H₂O₂) rapidly decomposes into water (H₂O) and oxygen gas (O₂) when catalyzed by the yeast. The yeast contains an enzyme called catalase that speeds up this decomposition reaction.

The dishwashing soap traps the oxygen gas produced during the reaction, creating a large amount of foam that looks like toothpaste being squeezed from a tube (hence the name "Elephant Toothpaste"). The reaction is exothermic, meaning it releases heat, which is why the bottle feels warm after the reaction.

The chemical equation for this reaction is: 2H₂O₂ → 2H₂O + O₂

QUESTIONS:

1. Why does this reaction foam more than the reactions in Experiment 5.2?

2. What is the role of yeast in this reaction?

3. Why does the bottle feel warm after the reaction?

HYPOTHESES:

Write your predictions about what will happen in this experiment and why.

PROCEDURE:

1. Put on safety goggles.
2. Rinse out the 250 mL flask.
3. Place the flask in a sink or take it outside (this will get messy!).
4. Add 75 mL of 30% hydrogen peroxide to the flask.
5. Add 2 tablespoons of dishwashing soap to the flask.
6. Add a few drops of food coloring of your choice.
7. In a separate measuring cup, mix a packet of active yeast with a little warm water.
8. Let the yeast sit in the water for about 5 minutes to activate.
9. Once the yeast is activated, quickly pour it into the flask with the hydrogen peroxide mixture.
10. Step back and observe what happens!
11. After the reaction slows down, feel the outside of the flask. It should feel warm.

VIDEO DEMONSTRATION:

Watch this video demonstration of the elephant toothpaste experiment to see the procedure in action.

OBSERVATIONS:

CONCLUSION:

Based on your observations, answer the following questions: