Today we are going to tell the story of Mentos and soda.

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Mentos soda fountain is a very famous small experiment. It has become popular on the Internet several years ago. Countless people have played it, and it has long been a rotten street.

if you think so, don't rush to walk. You'll say something new today: do you know what kind of soda gets the highest spray on Mentos?

someone actually did the experiment, and the results were published in the Journal of Chemical Education (Journal of Chemical Education). They collected two liters of common carbonated drinks and soda with pure carbon dioxide and water, put 11 Mentos mints in each bottle, and measured the height of the fountain.

what's the result? As shown in the picture below, the highest spray of these sodas is the cherry-flavored Dr pepper sugar substitute. A more common rule is that sodas that use sugar substitutes generally seem to spray higher, and sugary versions are better at forming fountains than pure sparkling water.

(this is a picture of Compound Interest based on the information produced by the original research, see: http://www.compoundchem.com/wp-content/uploads/2017/05/The-Secrets-of-the-Coke-and-Mentos-Fountain.png)

so, if you want a powerful soda fountain a few meters high, you can try those sugar soda

principles? Let's start with the reasons for the formation of the fountain. The essence of the soda fountain is that carbon dioxide escapes from the supersaturated solution to form foam. When the beverage bottle is not opened, the pressure in the bottle is higher, and the pressure increases the solubility of carbon dioxide, which can be dissolved in water. Open the bottle cap, the pressure suddenly drops, the water can not dissolve so much carbon dioxide, at this time the drink becomes a supersaturated solution of carbon dioxide, so the excess carbon dioxide naturally becomes bubbles.

that said, the bubbles actually came out quite slowly without the Mentos. because forms bubbles from scratch in the solution, which is not an easy task. this can be explained by surface energy or force. Simply put, the interface of a very small bubble is so bent that it has to overcome a lot of additional pressure before it can exist.

and Mentos actually has a lot of rough surface, which provides a good "core" for the formation of bubbles. Attached to these rough and uneven places, you can directly form larger, less bent bubbles, so that the additional pressure on the bubbles will be reduced, and it will become quite easy to form, so a large number of bubbles will be produced in a very short time.

(what Mentos looks like under an electron microscope, these rough areas provide the "nucleus" needed to form bubbles. Many other things actually have the same effect, such as sprinkling some salt will also make Coke pop up suddenly)

. As for the difference between different sodas, it doesn't mainly depend on the steps of bubble formation. The researchers found that a series of common substances in soda, such as sugar and citric acid, can more or less promote the height of the fountain. this is mainly because the presence of these solutes prevents small bubbles from merging together to better maintain delicate and rich bubbles.

after they added solute to soda water, they also found that the bubbles became more delicate:

different soda fountains are different. If you are interested, you can also try it yourself. Except for the trouble of cleaning, there is no special problem _ (: cleaning "∠) _

Journal of Chemical Education is a very interesting journal. The main content is that teachers delve into how to do fancy experiments to teach students

surface tension. It may be quite complicated to talk about it in detail. If you want to know more, you can read the original article (there are also many other motion pictures related to surface tension).

reference source: http://pubs.acs.org/doi/abs/10.1021/acs.jchemed.6b00862