ChEmIcAmAzInG - The Mentos Diet Coke Geyser

Welcome everybody to a new Snooping Session. Let's start with a question: Have you ever seen amazing chemical reactions? I'm sure you have, at least once. Thanks to the Internet, plenty of videos are made every day showing these wonderful processes. But most of the time you just see a video, without explaining why what you are witnessing is happening. Well, my Snoopers, ChEmIcAmAzInG will do the job. Here to simply describe the reality behind the wonder....
Let's start with one of the most common reactions. Maybe some of you have tried this before. I personally have, and by the time I did it it gets very, very, very messy. This is the Mentos Diet Coke Geyser.

Everybody that has a computer and a social media should know this trick, and if you have ever wondered WHY the reaction between Diet Coke and Mentos is so strong.... Keep reading for the answer.

First of all, it should be noticed this is not a “strict ingredients reaction”; lots of other carbonated beverages will also readily react adding Mentos, and even some multivitamin pills have the same characteristics needed to perfectly react with Soda drinks. And did you know that, while in the beginning carbonation was added because it was thought it was beneficial to the human body, today carbonation is added for very different reasons, including taste and shelf life. Introducing CO2 into the drink mix under pressure, makes the drink slightly more acidic (carbonic acid), which has the purpose to sharpen the flavor, producing that slight burning sensation soft-drinkers love. It also provides the drinks with preservative properties, which increase the shelf life of the beverage.

What happens is that Mentos is a mint with thousands of small pores on its surface, breaking the polar attractions between the water molecule. This disruption creates thousands of ideal aggregation sites for the gas molecule, just like a proton pack for the gargantuan amount of little carbon dioxide bubbles in the drink. But this would happen only If the mint has a porous surface. Unfortunately, If you wanna try right now using a smooth surfaced mint, I’m afraid you have to go to the shop because you won’t get an epic reaction.
The aggregation of bubbles and their growth in size will quickly cause the bubbles to leave the site and rise to the surface of the cola.  Bubbles will continue to form on the porous surface and the process will repeat, creating a fantastic foamy effect.

But the “bubble explosion” is not the only responsible. In addition to that, the arabic gum mixed with the gelatin ingredients of the Mentos, combined with the potassium benzoate, sugar or aspartame, in Diet cokes, also help in this process. In these cases, the gum, which is part of compounds called surfactants,  end up lowering the surface tension of the liquid, allowing for even more rapid bubble growth on the surface of the Mentos. This helps because without surfactants, bubbles would form more difficultly.

And this would give you a good reaction. But another very important ingredient that explains why Diet Coke (and mainly all the soda drinks) produce such a bigger reaction, it’s because aspartame lowers the surface tension of the liquid too. And this contributes very much, much more than sugar or corn syrup will.  So a good way to increase the result is adding more surfactants to the soda before you add the Mentos, like adding a mixture of dishwasher soap and water.

Another factor contributing to the size of the geyser is how rapidly the mint sinks in the soda.  The faster it sinks, the faster the reaction can happen, giving you a bigger geyser; a slower reaction may release the same amount of foam overall, but without the explosion you miss half of the fun, right? This is the reason why Mentos works so much better than other similar brands.  Mentos are quite dense objects and so tend to sink rapidly in the cola. If you crush the Mentos, it won’t sink much at all. And you won’t get the explosive-like reaction.

But it's not over. Yet another factor that can affect the “greatness” of the reaction is temperature. The higher the temperature, the bigger the geyser. This is because gases are less soluble in liquids with a higher temperature. So, basically, they are more “ready” to escape the liquid, giving you a faster reaction.

But of course Caffeine, molecule of which I have spoken a lot in my Discovery Central, inside the Coke should increase it…… No, I’m afraid this is not the case. Of course it will help, but just because of the relatively small amount of it found in a typical bottle of soda generally used for these sorts of tricks.  If you add enough caffeine, you will see a difference, but if you really wanna see a radical difference, you will need an amount of Caffeine that would kill you. Well, kill you if you actually dare to consume the whole beverage. Which would mean you are very clever ;P

Rumor has it that also the acidity of the soda is a major factor in the resulting process. This is not the case either.  In fact, the level of acidity in the Coke before and after the Mentos geyser doesn’t change, denying the possibility of an acid-based reaction. If you want such a reaction, you should try with baking soda.

This is a funny thing to do with friends, and now you know the chemical reason why you'll have to clean up a sticky disaster (unless you do it outdoor, just saying). This is not an harmful trick, and if you've heard that people have died from drinking Diet Coke and  Mentos, this is just an urban legend. First because drinking soda releases some of the carbonation in it, avoiding the possible effect. Secondly, even if one did get a strong reaction, the foam will completely drop out of your mouth, which there have been numerous recorded instances of. The current world record for the most geysers to be set off simultaneously happened on October 17, 2010 and included 2,865 such geysers. So, now it's up to you. Try it, If you dare....