Who Needs Old Faithful?

Pop Mentos 2012

The Explorers finished a year of science activities in May with a series of soda pop geysers that put the famous Old Faithful to shame. Not to mention the fact that OUR geysers went off on whatever schedule we wished.

If you’ve ever seen the result of dropping Mentos candies into 2-liter bottles of pop, you’re familiar with this activity. While it is guaranteed to create crowd-pleasing eruptions of soda, not everyone is aware of just WHY this happens. It all has to do with the properties of soda and a little-known scientific concept called “nucleation.”

Soda pop is really just a flavored liquid with dissolved carbon dioxide gas—this dissolved gas is what gives the pop its fizz. If you’ve ever noticed the sound of some of this escaping gas when a pop bottle is first opened—or if you’ve ever been unfortunate enough to open a bottle that has been shaken—you have seen that the carbon dioxide in the soda really, really wants to change into its natural (at room temperature) gaseous form. It is relatively difficult for the carbon dioxide molecules to do this quickly, however, while they are essentially trapped in the liquid. Difficult, that is, unless they are given some sort of solid surface to grab onto—in that case, the molecules can latch on to one another and change into a gas phase much more quickly than normal.

This is really what nucleation, that obscure word we mentioned earlier, means: a rapid change from one physical state to another, such as changing from a liquid to a gas. The Explorers first tested this idea out with their fingers and a paper towel: placing either one into a cup of pop makes a bit of a fizz as the molecules join up into a gas. Mentos candies do the same thing, but far more efficiently. Even though they feel smooth to the touch, their surfaces are actually covered with tiny little microscopic pits—sort of like the dimples of a golf ball, but a whole lot smaller.

When the candies are dumped into a bottle of pop, those little pits become like an irresistible dance club for all of the carbon dioxide molecules dissolved in the pop. The molecules latch onto the pits, and then onto each other, and essentially flash into a gas. Of course, when a substance changes from a liquid to a gas it expands, and here it is doing it rather explosively. There is no room for the gas to expand inside the bottle, so it does the only thing it can—it forces the liquid out of the bottle opening. Presto, a pop geyser.

After a short demonstration, Mr. Ramsey showed the Explorers a couple of “pressurizers.” These are little tubes (one commercially bought, one homemade) that attach to the top of a bottle. They allow for an easier method of getting the candies down into the bottle, and they also have much smaller openings at the top. These smaller openings create greater pressure for the escaping pop, making the resulting geysers shoot considerably higher into the air.

The students had themselves a grand old time shooting off their pop bottles. Their parents might have been less thrilled to find pop-soaked kids waiting for a ride home afterward. Hopefully everyone had a towel to sit on for the ride home!

Check out the gallery to see some pictures from our pop geyser activity. Thanks to Mrs. Armstrong for the use of some of her photos as well!

P.S. One other thing—if you want to try this at home, it doesn’t matter what flavors or colors you use, but use diet pop instead of “regular.” Regular pop has some ingredient that makes it much more sticky than the diet varieties, making diet pop geysers much simpler in terms of clean-up!

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OH - Dayton / Wright-Patterson Air Force Base

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Reported on:
Sat, 08/20/2016 - 12:58