How do Coke and Mentos Work?
Written by: Richard Xu, Caleb Ng, Carmen Chau, and Jeffrey Lau
INTRODUCTION
The majority of us have probably experimented with dropping multiple sugary, round mentos into a bottle filled to the brim with coke. A large fountain of coke then comes rushing out, oftentimes multiple metres in the air, causing a sticky mess all over the place. It’s a fascinating experiment that can get young students interested in science, but we over here at Quantum Outreach have long pondered about the science behind this phenomenon. What properties do coke and mentos have that enable them to react so vigorously with each other? Today, all of that will be answered in our article down below!
HISTORY OF THE COKE AND MENTOS EXPERIMENT
The first Coke and Mentos Experiment was conducted on the Late Show with David Letterman in 1999 by “The Marek’s Kid Scientists’’. After this, two interested scientists from the entertainment company EepyBird, Fritz Grobe and Stephen Voltz decided to post a Youtube video demonstrating this experiment and it went viral, gaining 120 million views. The video was titled “Extreme Diet Coke & Mentos Experiments”. Afterwards, Grobe and Voltz appeared on many renowned television programs, such as Ellen, HBO’s The Comedy Festival to talk about their viral video and they were even invited to other countries like France, Turkey and Belgium. Big news media outlets like The Wall Street Journal, Rolling Stone and GQ Magazine wrote about the experiment which helped it become known worldwide like we see today (Grobe & Voltz, n.d.).
WHY DO THEY REACT IN THIS WAY?
Originally it was thought that the colossal fountain of soda spraying out of the bottle was caused by the caffeine in Coke. However, as more experiments were done, some using Diet Coke which has zero caffeine, this theory was ruled out. Next, some thought that the pH of the liquid was responsible for the vigorous reaction. Coke has a pH of 2.3 and it made intuitive sense that an acid-base reaction could explain the sudden explosion of sugar. This hypothesis was also proven false as the pH of the substance did not change after the reaction (Muir, 2008). So what really causes this phenomenon?
The answer is a process called nucleation (Grobe & Voltz, n.d.). Carbonated beverages are full of dissolved carbon dioxide gas (CO2) which makes bonds with the water molecules. The pressurized conditions of the bottle and the surface tension of the water keep the gas in solution, even though it wants to escape (the gas that escapes makes the fizzy sound you hear when you open the bottle) (Science Buddies, 2012).
“Nucleation sites” are the regions where the carbon dioxide gas gathers and forms bubbles. As long as there is a high surface area to volume ratio, that area can be classified as a nucleation site (Grobe & Voltz, n.d.). Although mentos look smooth, they are in fact covered with layers upon layers of bumps and rough edges, making them filled with nucleation sites. When they are dropped into the soda, these sharp edges break the bonds between the dissolved gas and water, allowing for the gas to turn into bubbles and escape (Science Buddies, 2012).
Mentos are heavy and can travel the entire volume of the bottle, breaking many bonds and building a lot of pressure that is released in the form of a geyser of soda (Grobe & Voltz, n.d.). Fast-moving mentos create larger explosions while slow, powdered mentos create tiny ones (Muir, 2008).
DIET COKE vs. REGULAR COKE
As mentioned earlier in the article, using either diet coke or regular coke alongside mentos can produce a spewing geyser of carbonation bubbles. However, is one better for use during an experiment? Turns out that diet coke, which gets its sweetness from artificial sweeteners such as aspartame, is more commonly used than its regular counterpart. While the reaction remains fairly the same regardless of what carbonated beverage you use for this experiment, diet sodas are usually more carbonated and fizzy compared to regular sodas. This all boils down to the presence (or lack thereof) of sugar. Since diet sodas lack the sugar that regular ones do, it has lower viscosity and surface tension. (Gruber, 2019). This, in turn, allows the soda to form smaller bubbles that can retain its structure for longer due to the reduced surface area of the bubble. Longer lasting carbonation bubbles, therefore, increases the height of the bubble geyser that forms a mentos and coke reaction.
Something else to consider about diet sodas is that they tend to be less sticky when released out in the open. This makes the cleanup process after the experiment easier, and less gross, as nobody would want to be all covered in sugary goop, especially on a hot summer day!
CONCLUSION
The beloved coke and mentos experiment is a perfect opportunity for young children interested in science to learn about the basics of acid and base reactions. It is very simple to do and requires minimal tools and equipment to execute correctly. Hopefully, this article can help you finally place a scientific explanation behind this iconic and messy science experiment.
REFERENCES
Buddies, S. (2012, June 14). Spurting Science: Erupting Diet Coke with Mentos. https://www.scientificamerican.com/article/bring-science-home-coke-mentos/.
Grobe, F., & Voltz, S. The Science of Coke and Mentos. EepyBird.com — Entertainment for the Curious Mind. http://www.eepybird.com/featured-video/coke-and-mentos-featured-video/science-of-coke-mentos/.
Gruber, B. (2019, December 18). Why Do Flight Attendants Hate Serving This Drink to Passengers in Flight? Retrieved January 31, 2021, from https://www.bravotv.com/top-chef/blogs/diet-coke-takes-longer-for-flight-attendants-to-serve-on-airplanes-bubbles#:~:text=Sugar%20both%20increases%20viscosity%20and,bubbles%20that%20pop%20much%20slower.%22&text=In%20the%20end%2C%20the%20total,out%20by%20a%20few%20seconds.
Muir, H. (2008, June 12). Science of Mentos-Diet Coke explosions explained. https://www.newscientist.com/article/dn14114-science-of-mentos-diet-coke-explosions-explained/.
Tobin, Declan. (2021). Amazing Facts About Diet Coke And Mentos Experiment. Easy Science for Kids. Retrieved from https://easyscienceforkids.com/diet-coke-and-mentos-video-for-kids/
