Watching a child's face light up as they observe a new science experiment always puts a smile on my face. Unfortunately, many believe that such activities are difficult, costly, or otherwise impossible to incorporate into lesson plans. Elephant toothpaste is a fantastic example of a quick, exciting reaction that only requires five ingredients.
When all the ingredients are mixed into a bottle, they become very foamy and often bubble out the top of the container. This earned the activity the name Elephant Toothpaste - the foam resembles toothpaste being squeezed out of a tube, but there's so much foam that only an animal as large as an elephant could use it!
I used a small tea bottle for my experiment, so if a one-liter soda bottle is used, double each ingredient. Let's get started!
Ingredients:
1/4 cup 3% hydrogen peroxide (higher concentrations will produce larger reactions)
1 tbsp dish soap
1 tbsp active dry yeast
1/4 cup warm water
Food coloring (optional)
Equipment:
1 bottle
Funnel
Tablecloth
Directions:
Set the bottle on the tablecloth to make clean-up easier. Put the funnel into the bottle so the ingredients can be poured in.
Put the dry yeast in a separate bowl, then pour the warm water on top. Stir it around until the solution can be poured. If too viscous, add more water.
Pour the hydrogen peroxide and dish soap into the bottle using the funnel. Squeeze a few drops of food coloring in as well. Swirl the solution around so it all mixes.
Pour the yeast solution into the bottle and watch the reaction!
This solution can be safely poured down a drain or wiped up with a wet cloth. Be careful! The food coloring may stain hands and clothing, and the hydrogen peroxide may irritate the skin if higher concentrations are used.
To Make An Experiment:
This activity is truly a demonstration rather than an experiment, for an experiment will follow the scientific method. Here are ideas for expanding upon the activity:
Use different concentrations of hydrogen peroxide (20-Volume, 7%, etc.) How does the speed of the reaction change? Are there more or less bubbles? Why did this change occur?
Change the amount of dish soap. What happens to the foam? Was this expected or did it come as a surprise?
Do the same experiment without any dish soap. What happened?
The Science:
Did you know that yeast is a living creature? This powdery substance is a type of fungus that we use to bake bread and brew drinks. It needs to eat just like all organisms do, and will assist in breaking down the hydrogen peroxide.
Hydrogen peroxide is made of two important elements - hydrogen and oxygen. When split by the yeast, it will break into water and oxygen gas. When gas is released, it makes bubbles. To make the foam appear, we want to trap these bubbles inside the liquid so they can't escape and rejoin the atmosphere. To do this, we add dish soap.
The dish soap increases the surface tension of the water. In other words, it makes the water stick to itself more than it did before, preventing the oxygen from leaving. Since gas takes up more volume than liquid, the foam expands when the liquid hydrogen peroxide produces gaseous oxygen. This reminds many of squeezing toothpaste out of a tube!
Some may notice that the bottle grows warm after the yeast is added. This is because the reaction is exothermic - heat is produced as energy leaves the hydrogen-oxygen bonds found in hydrogen peroxide.
Did your students and children enjoy this activity? Sixteen more are available for download as PDFs.