The Decomposition of Hydrogen Peroxide

Introduction

Something decomposes when it breaks down into its component parts. 

The chemical formula for hydrogen peroxide is H₂O₂.  It looks pretty similar to the chemical formula for water, which is H₂0, except that hydrogen peroxide has an extra "O", an extra oxygen.  Hydrogen peroxide is not a very stable compound, so, it is always decomposing to water and oxygen, but under normal conditions, the decomposition goes very slowly.  In this reaction, yeast catalyzes the decomposition, making the reaction go much more quickly.  If you add a little dishwashing detergent, you get foam!  If you add food coloring, you get colored foam!

Safety

• Make sure you have an adult helping you.
• Do this experiment in the sink!

Supplies

• An empty 20 oz soda bottle (or any tall skinny clear container)
• Hydrogen peroxide (you can get 3% at the grocery store, or 8% at a beauty supply store)
• Active yeast
• Warm water
• Liquid dish soap
• Food coloring - optional - but it does make a nice color!

Directions

1. Mix ~4 oz of hydrogen peroxide with ~2oz of liquid dish soap and a few drops of food coloring.   Add this mixture to the soda bottle and place it in the sink.
2. In a separate container, mix one packet of active yeast with warm water, still and let sit for ~ 5 minutes.
3. When you are ready, pour the yeast mixture into the soda bottle (a funnel might be helpful) and watch the reaction!

Observations

• How much foam is produced, and how quickly?
• Does it matter if you use lukewarm water to activate the yeast or cold water?
• What happens if you add more or less soap? 
• What happens if you don't add any soap?

What's Happening?!?

Hydrogen peroxide (H₂O₂) decomposes into water and oxygen gas, but normally the reaction is so slow as to be imperceptible.

2H₂O₂2H₂O + O₂(g)

What happens when you pour hydrogen peroxide onto a cut? It bubbles! That's because there is something in your bodily fluids that catalyzes the decomposition. A catalyst is a substance that speeds up a reaction, without being consumed itself.

In this experiment we use a 3% hydrogen peroxide solution. The production of oxygen gas is made more noticeable by adding some dish soap, which makes the foam. The reaction is catalyzed by the active yeast added to the container. The yeast changes the mechanism, or pathway, by which the reaction occurs. The rapid production of bubbles of oxygen gas, along with the dish soap, quickly creates a large quantity of foam.

Have questions?  email us!

Experiment furnished by Angela Howard of the Society of Women Engineers.