Chem Matters - The Mentos & Diet Coke Craze
Summary
This article published by Chemmatters, a branch of the American Chemical Society, refers to the explanation and reasoning behind the famed “Diet Coke and Mentos Experiment.” For those unfamiliar with this particular experiment, it involves taking Mentos candies (a chewy mint) and 1 2-L diet soda (specifically Diet Coke), and dropping the Mentos into the soda. The introduction of the Mentos to the soda results in a reaction in the form of a geyser of soda erupting from the bottle. According to this article, the infamous experiment has little factual information written about it in contrast to the hundreds of thousands if not millions of people to have performed the experiment.
The initial observations one must make to understand this reaction is that when the soda is originally bottled and shipped it is pumped with C02 to give it the “fizz” soda is known for, but in order to get that fizz the soda must be pumped with an amount of C02 much more than needed. The carbonation eventually dissipates over time after opened, and is effected by variables such as room temperature. An equally important variable is the texture of the surfaces in contact with the soda, as a rough bumpy texture is more prone to capture C02 molecules in microscopic dimples where they will become bubbles, the process in which bubbles form is known as nucleation. When bottled, soda containers are as smooth as possible to reduce nucleation, but Mentos have a rather rough and bubbly texture, which acts as the perfect environment for nucleation.
The reaction of Mentos and Diet-Coke is caused by nucleation, as when the Mentos are dropped in the soda and stir up the solution, the rising C02 molecules are trapped in the millions of pits in the candy. This leads to nucleation -molecules collectively form large bubbles of C02 gas - by the millions, which results in the newly formed C02 bubbles. This can be proven to be the source of the reaction as if the candy is rubbed with a moist paper-towel, the reaction is significantly reduced by about half, as the paper-towel greatly reduces the number of bumps thus there is less nucleation. Another supporting theory of this is,
the gum arabic (and also coconut oil in the Mentos) is a nonpolar, oily gum that helps the carbon dioxide bubbles to get free because oil and water don’t mix. The water molecules in the matrix become more attracted to each other because they are repelled by the oil, and so it takes less energy for the carbon dioxide to break free. (Diet Coke & Mentos pg 4)
This theory related to atomic bonds is another speculated reason as to why this reaction results in a fountain. This theory is largely respected as it changes the focus from a physical reaction as previously speculated, to a chemical reaction. It implies that the water molecules bond as they are repelled by the oil molecules meaning that they will reach the mouth of the bottle with more mass and force resulting in less energy to break the surface tension and a larger fountain.
Conclusively, this reaction is caused by the Mentos capturing C02 molecules in its millions of tiny bumps, resulting in nucleation (forming bubbles) which when reach surface release into the atmosphere some bringing soda out of the water causing the soda to geyser.
The initial observations one must make to understand this reaction is that when the soda is originally bottled and shipped it is pumped with C02 to give it the “fizz” soda is known for, but in order to get that fizz the soda must be pumped with an amount of C02 much more than needed. The carbonation eventually dissipates over time after opened, and is effected by variables such as room temperature. An equally important variable is the texture of the surfaces in contact with the soda, as a rough bumpy texture is more prone to capture C02 molecules in microscopic dimples where they will become bubbles, the process in which bubbles form is known as nucleation. When bottled, soda containers are as smooth as possible to reduce nucleation, but Mentos have a rather rough and bubbly texture, which acts as the perfect environment for nucleation.
The reaction of Mentos and Diet-Coke is caused by nucleation, as when the Mentos are dropped in the soda and stir up the solution, the rising C02 molecules are trapped in the millions of pits in the candy. This leads to nucleation -molecules collectively form large bubbles of C02 gas - by the millions, which results in the newly formed C02 bubbles. This can be proven to be the source of the reaction as if the candy is rubbed with a moist paper-towel, the reaction is significantly reduced by about half, as the paper-towel greatly reduces the number of bumps thus there is less nucleation. Another supporting theory of this is,
the gum arabic (and also coconut oil in the Mentos) is a nonpolar, oily gum that helps the carbon dioxide bubbles to get free because oil and water don’t mix. The water molecules in the matrix become more attracted to each other because they are repelled by the oil, and so it takes less energy for the carbon dioxide to break free. (Diet Coke & Mentos pg 4)
This theory related to atomic bonds is another speculated reason as to why this reaction results in a fountain. This theory is largely respected as it changes the focus from a physical reaction as previously speculated, to a chemical reaction. It implies that the water molecules bond as they are repelled by the oil molecules meaning that they will reach the mouth of the bottle with more mass and force resulting in less energy to break the surface tension and a larger fountain.
Conclusively, this reaction is caused by the Mentos capturing C02 molecules in its millions of tiny bumps, resulting in nucleation (forming bubbles) which when reach surface release into the atmosphere some bringing soda out of the water causing the soda to geyser.