Adding Mentos candies to a bottle Diet Coke (or any carbonated beverage) causes a stream of fizzy fluid to jet out of the container. The rough surface of Mentos candies is thought to contain innumerable nucleation sites that catalyze rapid degassing of dissolved CO2 from the beverage: CO2(aq) → CO2(g) It is argued that beverage surface tension as well as beverage/candy additives affect the degassing process, but the action of these variables during the nucleation process and fountains produced remains unclear. Using a various kinetic experiments, we have explored the role of food & beverage additives, ambient pressure, and beverage CO2 concentration in this experiment. These investigations have provided insight on the role of additives, mechanisms of bubble formation, foam production, and degassing. Our results indicate that the degassing kinetics (and therefore fountain heights achieved) are affected by beverage additives but not food additives. Perhaps unexpectedly, beverage CO2 concentration affects the speed of degassing. Interestingly, fountain heights are affected by ambient pressure. Contrary to popular claims, our results suggest that beverage surface tension does not play a major role in the fountaining effect. Our results fit with a simple theoretical model which postulates that degassing occurs as CO2(aq) diffuses into pre-existing gas cavities on Mentos candies that are introduced into beverages. Furthermore, the data are in good agreement with a simple kinetic mechanism for foam production and decay. The experimental protocols described herein have been used in outreach events, high school chemistry courses, university courses for non-science majors, general chemistry courses, physical chemistry courses, and research projects for undergraduates. Thus, the theory and experiments presented may be tailored to match the chemical sophistication of a wide variety of audiences.

Possible mechanism of bubble formation and growth in the Diet Coke and Mentos experiment

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.