Mentos-Diet Coke Reaction

Thursday, June 12, 2008

Tara Gidus, MS, RD, CSSD, LD/N

Have you heard about this experiment that some people have done with Mentos and Diet Coke? If you put a Mentos into a bottle of Diet Coke, it causes a geyser type reaction, causing the Diet Coke to shoot up with a powerful force. I have heard people talk about this and claim that it proves that Diet Coke is bad for you. I don't see how it proves that anything is bad for you, but simply that a reaction happens.

Some students at Appalachian State University actually studied why the reaction happens. They just published their results in the June 2008 issue of the American Journal of Physics. Here is what they found:

"In an opened container of soda, carbon dioxide gas bubbles out over the course of minutes or hours until the concentration of carbon dioxide left in the soda is proportional to the carbon dioxide in the surrounding air. This de-fizzing reaction is slow because the surface tension of the liquid is very high, which keeps the gas bubbles trapped.

But when a Mentos is dropped in the beverage, it breaks the surface tension and as it falls the candy’s surfactant coating further reduces the surface tension of the liquid. The candy’s rough surface also provides growth sites for the gas, making it easier for carbonation to escape as a foam geyser.

The geyser also occurs when sand, salt or lifesavers were added to the Diet Coke, but the mass lost and volume traveled is much less spectacular."

I will be able to sleep better tonight now knowing why this reaction happens, how about you? If you do decide to try this experiment at home, use caution when you drop it in and run for cover. The liquid can explode nearly 30 feet!

Photo courtesy of oatmeal2000

Labels: Tara Gidus

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