Q: How does the type of container you use affect the Elephant Toothpaste demonstration?

I’ve written before about the elephant toothpaste demonstration, in which the decomposition of concentrated hydrogen peroxide is sped up using a catalyst to create fast-forming foam.  When this reaction is performed for a show or in a lab, the demonstrator usually uses a graduated cylinder, beaker, or Erlenmeyer flask- all common chemistry laboratory glassware.

(Left to right) Beaker, graduated cylinder, Erlenmeyer flask

Creative containers can add some extra fun.

For example, my college group would sometimes use soda pop bottles for demonstrations off campus.  Because the bottles were plastic, they were easily transportable and wouldn’t break like the glassware.  But the real reason we liked to use pop bottles was that the foam would shoot out higher with the bottles than the glassware.  With beakers and graduated cylinders, the base of the container is the same size as the opening at the tops.  An Erlenmeyer flask has a narrower neck than the base, but we found that pop bottles had even narrower necks than our flasks.  In the elephant toothpaste demonstration, as the foam builds up, it is forced out of the container.  With the smaller openings in the pop bottles, the foam was pushed out quickly to make room for more foam.  The increased pressure in the bottle caused the foam to burst out like a geyser.

One time, when we were practicing the demo with a 2-liter bottle, the foam was forced out so powerfully that it hit the ceiling in our lab.  There was still a stain on the ceiling tile several years later.  (We were never able to recreate the experience- partly because our faculty advisor banned us from trying.)

If we were running this demo in October, we would sometimes add pumpkins to the mix.  By running the reaction in a carved pumpkin, the foam is pushed out through the face openings.  Because foam usually slipped out through the mouth first, we would call this demo “puking pumpkins.”

We were such an imaginative patch.  (Get it?  Like a pumpkin patch?  … OK, I’m not that funny.)

Keep calm and science on.


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