Diet Coke and Mentos What is really behind this physical reaction? Spring 2007 PHY2210 Class Background on the Reaction The abrupt ‘fountain’ response of diet soda mixed with mint-flavored Mentos is well documented and much debated. It has been speculated that the cause of this phenomenon is most likely a combination of two physical reactions, related to the release of pressurized carbon dioxide contained in soda. 1) The surface roughness of Mentos provides many nucleation sites for CO2 bubbles to form, and 2) the gum arabic found in Mentos significantly reduces surface tension, allowing rapid escape of CO2. This semester, our PHY2210 class has conducted a series of experiments to clarify whether the intensity of the reaction is due more to the surface roughness of the candy or to the gum arabic contained in it. We selected materials, organic and non- organic, based upon their surface roughness and gum arabic content or lack thereof. These include: Mentos, Cake Mates, Wintergreen Lifesavers, liquid Gum Arabic, playground sand, and granular salt. An SEM is used to determine surface roughness microscopically (up to 10,000x magnification). We constructed a bottle stand (10 degrees off vertical) and a delivery mechanism for the materials to maintain consistency in our results. Gum arabic is administered by direct injection. Intensity of reaction is determined by measuring the amount of liquid remaining in the bottle 5 seconds after the material is dispensed. We report results comparing gum arabic concentration and surface roughness vs. reaction explosive power. There is almost a direct correlation between fountain height and weight of the bottle after the trial. The height data here is estimated based on video capture, and represents the highest fountain created across either trial. The most interesting result is the Dawn/water mixture producing a fountain nearly 2x the height of the Wint-o-Green fountain while they had nearly the same remaining mass. Testing the Reaction Mentos Wint-o- Green Lifesaver Dawn/Wat er MixtureSalt Cake MatesSand Liquid Gum Arabic Trial Trial Mass of Diet Coke Bottle Post Explosion (in g ± 0.1)* Mass of 2 Liter Diet Coke Bottle Prior to Explosion: (5 Measurements, in g±0.1) 2041 | 2029 | 2016 | 2036 | 2037 Avg = g Mass of Wint-o-green Lifesavers, Cake Mates, Salt, Sand, and final Mentos runs in g±0.1: 30g Volume of Liquid Gum Arabic and Dawn/Water Mixture Injections in mL±0.5: 10mL Abstract The larger the mass from the table and graph above, the less explosive the reaction for the particular material. Thus Mentos produced the most powerful reaction and liquid gum arabic was the weakest. *Materials listed in increasing order of mass remaining, not in order of trials Scanning Electron Microscope Material Images** Salt Sand MentosCake Mate Lifesaver Conclusion Our two variables in the experiment were materials containing many nucleation sites (having rough surfaces) and materials containing gum arabic. We found that both gum arabic and nucleation sites played a major role in causing a reaction with the Diet coke. Salt (rough surface) and the Cake Mates (gum arabic) had similar amounts of Diet Coke left in the bottle after their reactions but the Cake Mates had slightly more. This shows that rough surfaces and gum arabic are about equally responsible for the reaction but that rough surfaces have slightly more influence than gum arabic does. This result shows us that it is not just one property of the Mint Mentos that causes such a powerful reaction when combined with Diet Coke. Therefore, Mint Mentos and Wint-o- green Lifesavers had the best reactions because they have a combination of both variables. It also explains why Mint Mentos has a better reaction than Wint-o-green Lifesavers, since Mentos have a more rough surface. **Images are approximately 2600x magnification Preliminary Data