05.28.08
Diet coke and Mentos
I know you love watching the videos and maybe you’ve tried it yourself…
Now someone has studied the reaction.
From the Chronicle of Higher Education:
Diet Coke and Mentos: Why the Reaction?
By JJ HERMES
It’s been well documented, both by David Letterman and in thousands of YouTube videos, that combining Mentos breath mints with Diet Coke produces a thrilling eruption. But why?
Tonya S. Coffey, an assistant professor of physics and astronomy at Appalachian State University, had her sophomore-level physics students answer that question, and she has published their findings in the June 2008 issue of the American Journal of Physics.
The students measured how far different concoctions sprayed and how much mass they shed in the reaction. They mixed Diet Coke and Fruit Mentos, Diet Coke and Wint-O-Green LifeSavers, Diet Coke and rock salt, and a dozen other combinations.
Ms. Coffey also trained a scanning-electron microscope and an atomic-force microscope on the mints, observing the minute patches of surface roughness that contribute to the explosive reaction.
The students confirmed that the ingredients most responsible for the physical reaction are potassium benzoate and aspartame, which reduce the amount of work required to form bubbles in the carbonated soda. Those bubbles help carbon dioxide rapidly escape in the do-it-yourself eruptions. They also found that, while Mentos cause Diet Coke to spray twice as far as do LifeSavers, both mints cause about as much soda to leave the bottle.
“We were very low budget,” says Ms. Coffey, who now faces a different problem. Since her students have figured out why the Diet Coke-Mentos cocktail is so volatile, she says, “I’ve got to think of a new experiment” for them.
