Supplies
Empty plastic bottle
3 percent hydrogen peroxide solution, available at nearly any drug or grocery store
One packet of active yeast was found in the baking section of the grocery store
Liquid dish soap
Warm water
Food coloring (to make the reaction look pretty)
Preparation
Set up in a sink or go outdoors. You will want to do the experiment in a location where it will be easy to clean up all the foam afterward.
Stand away from the bottle once you add all the chemicals for the reaction. Hydrogen peroxide can irritate the skin and discolor clothing, even in low concentrations.
Steps
Carefully pour ½ cup hydrogen peroxide into the plastic bottle and add a big squirt of dish soap. Swirl gently to mix.
Add 2 to 3 drops of food coloring to the solution. (If you want to give your foam stripes, put the drops on the edge of the bottle’s mouth, but do not mix them in.)
In a separate container, mix 1 tablespoon of yeast and 3 tablespoons of warm water. Wait about 5 minutes for the yeast to activate.
Pour the yeast solution into the bottle with hydrogen peroxide.
Step back and watch foam squeeze out like a tube of elephant-size toothpaste!
Why It Works
You might be familiar with hydrogen peroxide as an antiseptic used to clean cuts and scrapes, which it does by killing bacteria. But what is it? It is a liquid made from hydrogen atoms and oxygen atoms (its chemical formula is H2O2). It is available in different strengths, or concentrations. You usually find it in a 3 percent concentration (although higher concentrations are available, they are more dangerous and must be handled carefully). It also breaks down when exposed to light, which is why it usually comes in dark brown bottles.
When hydrogen peroxide breaks down, it turns into oxygen (O2) and water (H2O). Normally this breakdown happens very slowly. But you can make that reaction happen faster! How? By adding a catalyst. Yeast is an organism that contains a special chemical called catalase that can act as a catalyst to help break down hydrogen peroxide. Catalase is present in almost all living things that are exposed to oxygen, and it helps them break down naturally occurring hydrogen peroxide.
This means that if you mix yeast with hydrogen peroxide, the hydrogen peroxide will rapidly break down into water and oxygen gas. The oxygen gas forms bubbles. These bubbles would usually escape from the liquid and pop quickly. But adding a little dish soap provides additional surface tension, allowing the bubbles to get trapped and creating lots of foam. This foam looks like a giant squeeze of toothpaste—almost big enough for an elephant!
You probably saw lots of bubbles and foam in this activity. What makes the foam appear? When the hydrogen peroxide comes into contact with the yeast it starts breaking down into water and oxygen. Oxygen is a gas and therefore wants to escape the liquid. The dish soap that you added to your reaction, however, traps these gas bubbles, forming a foam. The reaction continues as long as there is some hydrogen peroxide and yeast left. Once one of them runs out it stops making new foam. If you tried the activity without dish soap, the reaction probably will still made bubbles—but not foam.
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