Elephant’s Toothpaste
DESCRIPTION:
Hydrogen peroxide is decomposed quickly in liquid soap with the help of a catalyst to
create a large volume of foam that grows out of a graduated cylinder. The soap bubbles
contain oxygen.
2H2O2
KI
2H2O
+ O2
TOPICS COVERED:
- decomposition reactions
- catalysis
- exothermic reactions
- evolution of a gas
- color change
- chemical change
- activation energy
MATERIALS NEEDED:
- 100-mL graduated cylinder
- 10-mL graduated cylinder
- 30% H2O2 solution
- 2 M KI
- dish soap
- food coloring (optional)
- tray to contain the foam in
PROCEDURE:
1. Place the 100-mL graduated cylinder in the tray
2. Add ~ 3 mL of dish soap to the graduated cylinder
3. Add 10 mL of H2O2
4. Add food coloring, and swirl to stir
5. Measure out 5 mL of KI in the 10-mL graduated cylinder
6. Add the KI to the large cylinder
ADDITIONAL COMMENTS:
Without food coloring the foam takes on a yellow brown color. Adding more peroxide will
increase the volume of foam (increase the amount of soap too.) Adding more/less KI will
increase/decrease the reaction rate. This reaction can also be done in a 100-mL
volumetric flask, but the flask is more difficult to rinse completely than the graduated
cylinder. Baquacil (a pool oxidizer) can be used instead of 30% H2O2.
http://sites.jmu.edu/chemdemo
JMU Department of Chemistry and Biochemistry
SAFETY:
The 30% H2O2 used in this demonstration is a strong oxidizing agent which can damage
the eyes, skin and respiratory tract, so wear gloves and always wear safety goggles.
REFERENCES:
“Elephant’s Toothpaste." Steve Spangler Science. Accessed 25 Jan 2010.
<http://www.stevespanglerscience.com/experiment/hydrogen-peroxide-eruption>.
STORY:
- For elementary students we typically begin by asking students what kind of pets they
have, then say that we have a pet elephant. Our pet elephant is so big that he needs a
lot of toothpaste which gets expensive, so we make our own.
- For older students we typically explain that when you are in college you are always
broke, so you don’t want to have to spend money on basic things like toothpaste.
Instead we make toothpaste for ourselves and in this case, it’s enough for the entire
hall.
http://sites.jmu.edu/chemdemo
JMU Department of Chemistry and Biochemistry