You may not know it, but the Elephant’s Toothpaste experiment is the perfect kinetics and heat flow lab for your chemistry students. In the Elephant’s Toothpaste experiment, oxygen is rapidly removed from hydrogen peroxide using yeast as the catalyst. The addition of some dish soap to this reaction results in a foamy mess. The foam quickly rises out of the reaction container and can resemble a giant tube of toothpaste, hence the name, Elephant’s Toothpaste.
Lab Set Up
The set up is pretty easy. I like to do everything in an Erlenmeyer flask (because it’s my favorite glassware) due to it’s lovely shape and narrow neck. You’ll also need a beaker to prep your second solution.
- In the beaker, add a tablespoon of active dry yeast and about 30 mL of warm water. Then stir well until most of the yeast is mixed in. The yeast may get lumpy, and this can be pretty stinky, just FYI.
- In a Erlenmeyer, mix about 100 mL of 30 or 40 volume hair developer. This is hydrogen peroxide, but stronger than the drugstore stuff. Gently swirl in some dish soap. You don’t want to make bubbles. You could add a few drops of food coloring to make this more interesting. Take the temperature for some calculations later.
- Put your Erlenmeyer in some kind of tray to capture all the spill over. I have sinks that are built into my lab counters, so we squeegeed the mess into the sink.
- Pour the beaker contents into the Erlenmeyer and quickly take the temperature. The temperature will rise. This happens because the peroxide releases energy upon removal of the oxygen, which is absorbed by the soapy foam.
Chemistry Applications
The measurements will look endothermic because it is hard to distinguish the system from the surroundings – it’s actually exothermic.
You can repeat with different amounts of reactants and gauge temperature differences, do a reaction without the yeast to show the need for the catalyst, or just do a second time to ensure data was properly collected.
My kids LOVE this experiment, and I will say, it looks great on an Instagram boomerang!
Calculations
We will do some thermodynamics calculations to determine the amount of heat energy exchanged during the reaction. We use the specific heat capacity equation to figure out how much heat energy is moving around during two trials of the experiment. If you’re looking for some other heat flow labs, check out this blog post.
Conceptual
If you are choosing to do this experiment before teaching kinetics, you could also use it in your thermodynamics unit. It’s clear that the reaction heats up. Oftentimes you can even see the steam! Students also are asked to determine what the elephant’s toothpaste lab would look like and what kind of data would be collected if the reaction were endothermic or exothermic before beginning.
Lastly, the students sketch a potential energy diagram of their findings, and write a really great conclusion paragraph.
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