Ethanol as a Probe for the Mechanism of Bubble Nucleation in the Diet Coke and Mentos Experiment

Abstract

The Diet Coke and Mentos experiment involves dropping Mentos candies into carbonated beverages to produce a fountain. This simple experiment has enjoyed popularity with science teachers and the general public. Studies of the physicochemical processes involved in the generation of the fountain have been largely informed by the physics of bubble nucleation. Herein, we probe the effect of ethanol addition on the Diet Coke and Mentos experiment to explore the impact that beverage surface tension and viscosity have on the heights of fountains achieved. Our results indicate that current descriptions of the effects of surface tension and viscosity are not completely understood. We also extend and apply a previously reported, simplified version of Brunauer–Emmett–Teller theory to investigate kinetic and mechanistic aspects of bubble nucleation on the surface of Mentos candies in carbonated beverages. A combination of this new theory and experiment allows for the estimation that the nucleation sites on the Mentos candy that catalyze degassing are 1–3 mm in size, and that between 50,000 and 300,000 of these sites actively nucleate bubbles on a single Mentos candy. While the methods employed are not highly sophisticated, they have potential to stimulate fresh investigations and insights into bubble nucleation in carbonated beverages.

How Many Bubbles Are in the Foam Produced during the Candy-Cola Soda Geyser?

“…This analysis yielded an estimate of 50 000−300 000 sites on a Mentos candy that actively nucleate bubbles sites, consistent with previous estimates from experiments conducted with Mentos and Diet Coke. 8 Based on the mass (about 2.7 g) and previously measured smooth surface area (8 cm 3 ) 6 of a Mentos candy, this translates to 19 000−110 000 nucleation sites g −1 and 6300−38 000 nucleation sites cm −2 . Interestingly, it was noted that the foam (and therefore gas volume) decayed much more slowly in Diet Coke than in Coca-Cola, indicating a more stable foam in the former as compared to the latter.…”

“…Mentos candies have been demonstrated to have pores with a radius of curvature of 2 μm, well above the critical limit. 7,8 Equation 4 may be rearranged to provide insight into the [CO 2 ] that must be exceeded (also known as the critical concentration, or [CO 2 *]) to support degassing from pores with a particular radius of curvature (r): 13−15…”

“…8 Experimental measurements have allowed for the estimate that each Mentos candy provides between 50 000 and 300 000 catalytic sites that actively nucleate bubbles. 8 Furthermore, nucleation sites in champagne and beer have been reported to release bubbles at a frequency of between 5 and 30 bubbles per second. 16,17 Therefore, it is no surprise that the addition of several Mentos candies to a bottle of fresh soda results in a fountain of foamy bubbles that sprays out of the bottle.…”

“…Because this experiment is simple to carry out and yields remarkable results, it has been popular among the general public for quite some time. The experiment has also found widespread use in science classrooms because it connects to a variety of physicochemical concepts including chemical kinetics and reaction mechanisms, 1−8 acid−base chemistry, 3 surface science, 5−9 bubble nucleation and coalescence, 1,4,7−9 inquiry-based learning, 10,12 gases, 1,11 solubility, 1,8,11 safety in the laboratory, 12 and atmospheric science. 7 Science teachers have employed a variety of techniques to quantify various aspects of the kinetics of this reaction, and these methods have been useful in elucidating various factors involved in the generation of the fountain.…”

“…When Mentos candies are dropped into a bottle of a carbonated beverage, a frothy fountain jets out that reaches a few meters high. It is well established that this stream of foam results when nucleation sites on the Mentos candies catalyze the rapid degassing of CO 2 from carbonated beverages: − Because this experiment is simple to carry out and yields remarkable results, it has been popular among the general public for quite some time. The experiment has also found widespread use in science classrooms because it connects to a variety of physicochemical concepts including chemical kinetics and reaction mechanisms, − acid–base chemistry, surface science, − bubble nucleation and coalescence, ,,− inquiry-based learning, , gases, , solubility, ,, safety in the laboratory, and atmospheric science .…”