Diet Coke and Mentos Eruption
Reeko will never forget the first time he discovered this unique experiment. He learned three very important things that he has never forgotten to this day. Firstly, if you mix Mentos and Diet Coke, you get a violent eruption that will spew a gallon of sticky cola on you before you can even blink an eye. As he passed through the lab animal house, on his way to the kitchen to clean up, he learned something else – rats love coke! Before he knew it, he had 50 of those little furry critters clinging to his lab coat, licking away at the sticky mixture that had drenched his jacket (and they jumped him from behind knowing that he wouldn’t be able to identify who did it). And finally, he learned that nothing is more funny that watching 50 jittery (coke really hypes them up), burping rats pointing at each other and trying to look innocent.
Before you go any further, please make sure you conduct this experiment outside! This experiment can be very messy. If by some chance, you skipped this paragraph and conducted the experiment in your living room, Reeko begs you, please tell your parents you got this experiment from Ben Frye the Science Guy’s web site.
Strangely (as if things could be any stranger around here), the cause of the reaction we’ll describe below, is purely physical – not chemical. Some liquids can be supersaturated with gas. Soda is a good example. Soda is chock full of carbon dioxide gas. A “nucleation site” is a spot where the gas bubble from the gas is able to form. A nucleation site can be any surface that is scratched or has specks of dust and has a high surface area. When you pour Coke into a glass, the sides of the glass are “nucleation sites” and allow the carbon dioxide in the Coke to release as bubbles and fizz. When pouring Coke into a glass, the surface area that the Soda contacts is really not that large – only as large as the area that the coke is contacting as it pours into the glass. If you poor the Coke fast, it touches a lot more of the surface and hence, fizzes more.
- Stand the diet coke bottle upright and unscrew the lid. Other soda types will work but Diet Coke seems to work the best (sugar molecules in regular sodas help keep the carbon dioxide in solution, slowing the reaction).
- Put a funnel or tube into the spout.
- Take a half pack of Mentos and pour into the funnel.
- RUN as fast as you can (screaming while you run adds a bit of excitement to the trick).
- A geyser of Diet Coke will come flying out of the bottle – very impressive to see. The world record is almost 3 stories high!
The primary reason for the effect has to do with nucleation sites and the extraordinary surface area of Mentos candy. Mentos have a very high surface area for their size and hence, a tremendous number of nucleation sites. The have dimples and hundreds of nooks and crannies that if you could spread them all out, would equal a much larger surface area than just the little piece of candy would seem to have. So with Mentos, you can pack a lot more surface area, or nucleation sites, into a very small space. Also, since Mentos are heavy, the sink to the bottom and react with the soda all the way down.
Dropping any object into the Diet Coke bottle will produce a smaller version of the effect but Mentos produce a spectacular eruption. Dropping anything into the Diet Coke speeds up the release of the carbon dioxide process by both breaking the surface tension of the liquid and also allowing bubbles to form on the surface area of the object. Still, Mentos candy pieces are covered in tiny dimples (a bit like a golf ball), which dramatically increases the surface area and allows a huge amount of bubbles to form.
Coke like many other soft drinks are carbonated. This is what gives the drink it’s fizz and what gives it that lively taste. Coke is bottled under pressure to ensure that the proper levels of carbonation are present when the drink is opened. When you open the bottle the excess gas rushes out of the bottle and a hissing sound is heard. The dissolved gas then slowly bubbles out of the drink. Eventually all of the gas comes out of the solution and we say that the soda is “flat” and tastes “Flat”.
Incidentally, this need to pressurize the soda containers is why it wasn’t until the 1960’s that you say soda come in cans. Many attempts were made before that date, but no one could figure out how to economically make a can like container that could withstand the internal pressure. If you find cans from the 1960’s you will see that they are much thicker than those today. Technology over the years has allowed for the fabrication of much lighter cans that can withstand the pressures.
Likewise, early construction methods for forming glass bottles was not as sophisticated as it is today. Hence, if you look at an old Coke Bottle, you will immediately notice that they are much thicker and heavier that today’s bottle. You will also notice that with today’s plastic bottles, if you happen to get a newly made bottle, will have a lot more gas in it when you open it. This is because the gas can slowly escape through the pores of the plastic bottle. The bottlers charge the bottle with enough gas so that it will yield a sparkling drink even at its expiration date. Keep the bottle in the garage for a year or so and when you open it will be flat. Not so with bottles and cans, unless they start to leak, they will retain their fizz for years.