Mentos and Diet Coke Geysers

The final week of lab this semester we did an experiment based on the Mentos and Diet Coke geyser phenomenon. I bought several “geyser tubes” from Steve Spangler which allow the operator to introduce 1 to 10 Mentos (or Mentos-shaped objects) into the soda bottle in a safe and reproducible fashion. There is not a lot of chemistry involved in this phenomenon but it does make a good activity to explore the scientific method. It has the added advantage of being performed out of doors. The students were divided into groups of three or four. They were asked to formulate a central hypothesis concerning the cause of the phenomenon. They then came up with several ways to explore the geyser phenomenon based on what they understood about its cause. The proposed experiments were collected and 5 were chosen that seemed doable and likely to yield useful information. There are at least five different parameters to play with in regard to the “standard” conditions of 24 oz. Diet Coke mixed with 5 Mint Mentos. 1) modify Mint Mentos, 2) replace Mint Mentos, 3) modify Diet Coke, 4) replace Diet Coke, and 5) modify conditions. Each group did all five experiments plus the standard conditions. The experiments were done outside and the height of the geysers was measured with 10 four measuring sticks. Students also recorded the volume of the liquid left in the bottle afterwards. The data from both lab sections was compiled and put on the course website. The students were asked to interpret the data in terms of explaining the phenomenon. There is at least one scientific article (“Diet Coke and Mentos: What is really behind this physical reaction?”) and one Journal of Chemical Education article (“Mentos and the Scientific Method: A Sweet Combination”) written on this subject. Student handout available at OChemOnline Wiki.

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