by Tom Kuntzleman and Ryan Johnson
Since 2018, Ryan Johnson and I have been studying how the Coke and Mentos experiment behaves at different altitudes.1,2 We started doing this by using a compact, easy-to-carry device that we could easily carry on various mountain hikes (VIDEO 1).
VIDEO 1:3 For a longer video that describes these experiments in more detail, see the video in reference 4.
As you can see, the device we use captures the foam generated when Mentos candies are added to bottles of Diet Coke. The generation of foam is powered by the release of carbon dioxide gas from beverages, nucleated by micrometer-sized pits on the Mentos surface:1
CO2(aq) à CO2(g) Equation 1
By doing these experiments at elevations that ranged from below sea level in Death Valley to the top of Pikes Peak, we learned that, indeed, the reaction produces more foam at higher elevations. This is for at least two reasons.1 First, Boyle’s Law ensures that the volume of gas released in the foam will be greater under the lower atmospheric pressure at higher elevations. However, a second effect also contributes: carbon dioxide gas escapes from carbonated beverages much more quickly under lower atmospheric pressure. The faster kinetics of release also contribute to greater foam volume.
Our foam collecting device did not allow us to view the effect of altitude on the “true” Coke and Mentos experiment. That is, the device doesn’t allow one to observe the fountain produced as seen in the famous, original reaction.
So, you can imagine that Ryan and I always wanted to observe how the original Coke and Mentos fountain behaved at various altitudes. This past summer, we got a chance to do just that (Video 2). We started experiments in Denver, CO, and drove up Pikes Peak, running the Coke and Mentos experiment at various elevations along the way. Overall, the experiments were run at elevations that varied by 2750 m (9000 feet) in elevation.
Video 2: Diet Coke and Mentos on a Mountaintop!5
We collected videos of each experiment and later analyzed them to produce a graph of the time-dependent behavior of each Coke and Mentos fountain at the different elevations we tested (Figure 1).
Figure 1: Time dependent fountain height observed upon dropping 10 Mentos candies into 2 L bottles of Diet Coke at 22oC. All bottles had the same expiration date. Each point represents the average of three trials.
As noted in both Video 2 and Figure 1, fountain heights increased with elevation (lower atmospheric pressure). It should be noted that the fountain height dipped a bit at the summit (data not shown). We attribute this loss in height to very high winds at the summit, causing disruption of fountain formation. Nevertheless, the overall trend of increasing fountain height with elevation was expected. However, we did notice an unexpected effect: The time to reach maximum fountain height appeared to be delayed at higher elevations (Figure 2; note also the shift to the right of the peaks in Figure 1).
Figure 2: Time to reach maximum fountain height at various elevations in the Coke and Mentos experiment. Conditions are identical to those in Figure 1.
We aren’t quite sure what might be causing the delay in time to reach maximum fountain height at higher altitudes. It could simply be that it just takes a longer time to make a taller fountain. While we aren’t sure, we are certainly up for any suggestions as to what might be happening here.
All in all, Ryan and I had a fantastic time doing these experiments and spending time together. Is anyone up for repeating these experiments at ChemEd 2025? I hear there are some mountains near Golden, CO….
Tom Kuntzleman and Ryan Johnson
Kuiper and Tycho (four-legged lab assistants)
References:
1. https://pubs.acs.org/doi/10.1021/acs.jchemed.9b01177
2. https://pubs.acs.org/doi/10.1021/acs.jchemed.3c00601
3. Speedy Science Clips: How does altitude affect Diet Coke and Mentos? Tommy Technetium YouTube Video. https://www.youtube.com/watch?v=SWpgRBr85PA
4. Coke and Mentos at 14,000 feet, Tommy Technetium YouTube Video. https://www.youtube.com/watch?v=NyUW0hXYGnU
5. Diet Coke and Mentos on a Mountaintop! Tommy Technetium YouTube Video. https://www.youtube.com/shorts/ke895qcDTdk
NGSS
Analyzing data in 9–12 builds on K–8 and progresses to introducing more detailed statistical analysis, the comparison of data sets for consistency, and the use of models to generate and analyze data.
Analyzing data in 9–12 builds on K–8 and progresses to introducing more detailed statistical analysis, the comparison of data sets for consistency, and the use of models to generate and analyze data. Analyze data using tools, technologies, and/or models (e.g., computational, mathematical) in order to make valid and reliable scientific claims or determine an optimal design solution.
Asking questions and defining problems in grades 9–12 builds from grades K–8 experiences and progresses to formulating, refining, and evaluating empirically testable questions and design problems using models and simulations.
Asking questions and defining problems in grades 9–12 builds from grades K–8 experiences and progresses to formulating, refining, and evaluating empirically testable questions and design problems using models and simulations.
questions that challenge the premise(s) of an argument, the interpretation of a data set, or the suitability of a design.
Scientific questions arise in a variety of ways. They can be driven by curiosity about the world (e.g., Why is the sky blue?). They can be inspired by a model’s or theory’s predictions or by attempts to extend or refine a model or theory (e.g., How does the particle model of matter explain the incompressibility of liquids?). Or they can result from the need to provide better solutions to a problem. For example, the question of why it is impossible to siphon water above a height of 32 feet led Evangelista Torricelli (17th-century inventor of the barometer) to his discoveries about the atmosphere and the identification of a vacuum.
Questions are also important in engineering. Engineers must be able to ask probing questions in order to define an engineering problem. For example, they may ask: What is the need or desire that underlies the problem? What are the criteria (specifications) for a successful solution? What are the constraints? Other questions arise when generating possible solutions: Will this solution meet the design criteria? Can two or more ideas be combined to produce a better solution?
Planning and carrying out investigations in 9-12 builds on K-8 experiences and progresses to include investigations that provide evidence for and test conceptual, mathematical, physical, and empirical models.
Planning and carrying out investigations in 9-12 builds on K-8 experiences and progresses to include investigations that provide evidence for and test conceptual, mathematical, physical, and empirical models. Plan and conduct an investigation individually and collaboratively to produce data to serve as the basis for evidence, and in the design: decide on types, how much, and accuracy of data needed to produce reliable measurements and consider limitations on the precision of the data (e.g., number of trials, cost, risk, time), and refine the design accordingly.