Creating a Mentos and Coke geyser is practically a right-of-passage for most kids. It’s explosive, messy, and great fun! But what is really going on when Mentos and Coke collide? Does this time-honoured backyard science experiment work with other sweets and/or soft drinks or is it dependent on some secret ingredients that only these big brands contain? Read on to find out!
One soft drink is very much like another, right? Yes—to some extent. This means you’d expect similar results whether you complete this experiment with Coca Cola, Fanta, soda water, or any other fizzy drink.
Thanks to the work of citizen scientists around the globe—accessible via the Internet—we now know that diet Coca Cola is the most effective soft drink when it comes to getting a good surge of spray.
While a wide range of soft drinks can be used for this experiment, using Mentos as your chosen candy is a must. Although other sweets, such as M ‘n Ms or Lifesavers, have a similar texture and appearance, Mentos has something going on at a microscopic level that other candies just don’t have. Each Mentos sweet has microscopic pits in its surface that act as nucleation sites.
A nucleation site is where carbon dioxide molecules that are dissolved in the soft drink come out of the solution and move to their gaseous state. This causes the rush of bubbly gas that escapes out the bottle. Because each Mentos has millions of pits, millions of carbon dioxide bubbles are formed in a very short space of time, resulting in the whooshing soft drink geyser.
Another factor that is at play is the weight of the Mentos. These candies are heavy enough to sink right down to the bottom of the soft drink bottle. Once the Mentos have settled down there, they wreak havoc, generating huge amounts of carbon dioxide and pushing all the liquid on top of them out through the bottleneck.
Citizen scientists have set out to find the combination of soft drink and Mentos that would satisfy Goldilocks by being “just right”, and have found that seven Mentos is about the right number for a satisfactory geyser. However, whether you’re using one, seven, or 17 Mentos, they must be dropped into the soft drink at the same time to produce the maximum geyser height. The easiest way to do this is to roll a piece of paper into a tube and place the Mentos inside, then release them in one fell swoop.
As for the amount of soft drink required, standard 1.5 or 2L bottles available in supermarkets are firm favourites.
There is no conclusive information on the Internet about the best conditions for this experiment, which opens an avenue for further experimentation.
Give it a go! Simply set up a bottle/Mentos combination to use as a control then proceed with subsequent experiments, changing only one variable at a time for each experiment. Variables you could change include: the type of soft drink, the amount of soft drink, the temperature of soft drink, the type of candy, or the number of Mentos or other candies. Rank each experiment according to the size of the geyser it produces.
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