Diet Coke and Mentos eruption
The numerous small pores on the candy's surface catalyze the release of carbon dioxide (CO2) gas from the soda, resulting in the rapid expulsion of copious quantities of foam. Although any carbonated beverage will produce a similar effect, the reaction was popularized using Diet Coke for seemingly producing the best results.
When the Mentos come into contact with the Diet Coke, a reaction causes the rapid formation of foam.
MythBusters concluded that the potassium benzoate, aspartame, and CO2 gas contained in the Diet Coke, in combination with the gelatin and gum arabic ingredients of the Mentos, all contribute to the formation of the foam.
The structure of the Mentos is the most significant cause of the eruption due to nucleation. MythBusters reported that when fruit-flavored Mentos with a smooth waxy coating were tested in carbonated drink there was hardly a reaction, whereas mint-flavored Mentos (with no such coating) added to carbonated drink formed an energetic eruption, supporting the nucleation-site theory. According to MythBusters, the surface of the mint Mentos is covered with many small holes that increase the surface area available for reaction (and thus the quantity of reagents exposed to each other at any given time), thereby allowing CO2 bubbles to form with the rapidity and quantity necessary for the "jet"- or "geyser"-like nature of the effusion.
This hypothesis gained further support when rock salt was used as a "jump start" to the reaction. A paper by Tonya Coffey, a physicist at Appalachian State University in Boone, North Carolina, confirmed that the rough surface of the Mentos candy helps speed the reaction. Coffey also found that the aspartame in diet soda lowers the surface tension and causes a bigger reaction, but that caffeine does not accelerate the reaction.
- "Mentos and Soda". MythBusters. Season 4. Episode 14. August 9, 2006. Discovery Channel.
- "Mythbusters: Diet Coke and Mentos MiniMyth". Discovery Channel.
- Muir, Hazel (June 12, 2008). "Science of Mentos-Diet Coke explosions explained". New Scientist. Retrieved 2009-09-20.
- Coffey, Tonya Shea (June 2008). "Diet Coke and Mentos: What is really behind this physical reaction?". American Journal of Physics 76 (6): 551–557. doi:10.1119/1.2888546.
- "Most Mentos and soda fountains". Guinness World Records. 2010-10-17. Retrieved 2011-05-27.
- Baur, John E. & Baur, Melinda B. (April 2006). "The Ultrasonic Soda Fountain: A Dramatic Demonstration of Gas Solubility in Aqueous Solutions". Journal of Chemical Education 83 (4): 577–580. doi:10.1021/ed083p577. (registration required)