Diet Coke + Mentos –> Total Fizz

by Gilbert Keith

You must have seen the mentos/diet coke video in the previous post. There, I mentioned that I will write about why it so happens that upon addition of mentos to a bottle of coke, all the fizz comes out.

It so happens that initally, even I thought that mentos contains some amount of Calcium Carbonate (CaCO3), and that the CaCO3 reacts with the carbonic acid and phosphoric acid present in most aerated drinks. However, that is totally not true. Upon close inspection, one can see that mentos’ ingredients are: sugar, glucose syrup, hydrogenated coconut oil, gelatin, dextrin, flavouring, corn starch and gum arabic. So, naturally, there wasn’t anything basic reacting with the acidic soda (haha, such an oxymoron).

Well, it turns out that the reaction is more physical than chemical and can be explained by the idea of surface tension. When you get a bottle of diet coke, the attraction among water molecules is high and the bubbles don’t just fizz out. However, adding mentos does a couple of things that makes the gas escape so vigourously. One of them is the fact that mentos has a lot of dimples at the microscopic level and thus, it allows the gas from the soda to form bubbles at these dimples and escape. How efficient, no? The same happens with almost uneven surfaces; the best example, which I assume everybody has witnessed, is ice. Upon addition of ice, aerated drinks generally should allow for more gases to be dissolved, because the temperature of the water is lowered; however, a lot of gases escape, which is explained by bubbles forming on these “nucleation sites”. Another reason is that when gum arabic is added to the soda, it breaks the surface tension of the water; the intermolecular forces become weaker (if I am not mistaken) and therefore, it becomes easier for gases to escape. Thus, when these two factors are combined, it becomes very easy for the gases to escape.

So, that’s that about mentos and Diet coke. I am going to try it out sometime myself and post it on the internet. 🙂