Elephant toothpaste on the David Letterman show – by Rajeev Goel

The following wonderfully fun post is shared by Rajeev Goel, the creator of Our Science Fair which I referenced in yesterday’s post about organizing a science fair.

A couple of weeks ago — Nov. 12 to be exact — David Letterman had Kid Scientists on his Late Show. This is something he does once every few months, and in this case, the Kid Scientists were his first guest on the show, coming on even before his A-list movie star, Amanda Peet. I applaud The Late Show for doing this, and I just think it’s an amazing idea. I love the fact that ordinary school kids are getting their chance at five minutes of fame. In a world where science isn’t considered the most glamorous of professions, these kids are basically selling scientific exploration as being fun, cool, and something to aspire to. It’s also noteworthy that the kids chosen to be on the program are diverse in terms of gender and race. On Nov. 12, he had a boy and two girls, one of whom was Asian Indian.

Many would agree that the first girl, “Heather”, had the most exciting demonstration. The video of her demo is here:

For the curious among you, I thought I would break down her demonstration.  It can be tough to follow everything she says on air, since things move along fairly quickly.
First, she says that she has two beakers of cyalume.  Cyalume is another name for the chemical “diphenal oxalate”.  But really only the red beaker contains cyalume, and in fact, it’s a mixture of cyalume and a special fluorescent dye.  The chemical formula for cyalume is:
The other beaker, the one with the clear liquid, contains a hydrogen peroxide solution:
12-year old Heather says that when you “mix the two together, they will undergo chemiluminescence.”  She proudly and patiently explains to Mr. Letterman that “chemiluminescence is when the chemicals will give off cool light due to the excitations in the electrons.”  The chemical reaction that takes place is as follows (from Wikipedia):
Wikipedia explains further:
By mixing the peroxide with the phenyl oxalate ester (aka, diphenal oxalate), a chemical reaction takes place; the ester is oxidized, yielding two molecules of phenol and one molecule of peroxyacid ester (1,2-dioxetanedione). The peroxyacid decomposes spontaneously to carbon dioxide, releasing energy that excites the dye, which then relaxes by releasing a photon. The wavelength of the photon—the color of the emitted light—depends on the structure of the dye.

Once they have their bright yellow glowing liquid, Heather asks Mr. Letterman to pour it into the giant graduated cylinder, which appears to already contain about half a liter of liquid dishwashing soap.  Then, she asks him to add the manganese dioxide:

Since manganese dioxide is actually a black powder, I can only assume that the black liquid in the measuring cup is actually a water-based manganese dioxide solution.  When Mr. Letterman adds this to the giant cylinder, the crowd goes wild.  As Heather explains, “The manganese dioxide will act as a catalyst and break down the hydrogen peroxide into water and oxygen gas.  The oxygen gas bubbles will get caught in the soap, and it will also get very hot.”  The chemical reaction is as follows:

As you can see, the manganese dioxide is not actually part of the equation.  That’s because it’s only a catalyst, and doesn’t actually get consumed as part of the chemical reaction.  Anyway, resulting the water and oxygen gas (and heat) all get mixed up in the dishwashing soap causing it to create enormous amounts of suds, enough to overflow the giant graduated cylinder.

Sometimes this demonstration is known as “elephant toothpaste” (for obvious reasons), and you can find numerous examples on the web of this experiment being performed by kids in their school chemistry labs.  For example, check out this video.

Well, I hope that helps clear things up, and now you know enough to try this out yourself, assuming you can get a hold of the chemicals.  If you do, please follow all appropriate safety precautions … these chemicals are dangerous, and the chemical reactions produce a lot of heat.
 
Please leave a comment if you enjoyed this post.  Teachers and science fair coordinators:  don’t forget to get your free science fair website at OurScienceFair.com.
 
Rajeev Goel

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