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VBS Day 3: Diet Coke Geyser

June 23, 2010

This evening for recreation the kids were split into teams of two and given two clear plastic ponchos.  One of them then had to pour a sleeve of Mentos into a bottle of Diet Coke while the other had a red plastic cup and attempted to catch as much of the falling diet coke as possible. 

Before the kids got their chance we talked Morgan into giving it a shot.  She did not know what was going to happen when the Mentos were dropped into the bottle and the look on her face was priceless as the coke shot up into the air. 

Becks eventually made her way outside with Mason who was happily munching on a Popsicle.  Pastor Greg talked her into partaking in the experiment with Kay who agreed to hold the cup while she put the Mentos down the neck of the bottle.  It was very funny and I took a video of them. My favorite part is Becks laughing in the background as she puts the Mentos in and then runs away from the geyser. 

When I got home I did a little digging to see why Diet Coke and Mentos reacted so violently.  Below is what I found at the New Scientist:

The rough, dimply surfaces of Mentos encourage bubble growth because they efficiently disrupt the polar attractions between water molecules, creating bubble growth sites.

Low surface tension also helps bubbles grow quickly. Measurements showed that the surface tension in water containing the sweetener aspartame is lower than in sugary water, explaining why Diet Coke creates more dramatic fountains than sugary Coke.

Another factor is that the coatings of Mentos contain gum arabic, a surfactant that further reduces surface tension in the liquid. Rough-surfaced mints without the surfactant did not create such large fountains.

Mentos are also fairly dense and sink rapidly, quickly creating bubbles that seed further bubbles as they rise. Crushed Mentos that fell more slowly created puny fountains that only travelled about 30 centimetres.”

Overall, tonight was a lot of fun and the kids had a blast creating coke geysers outside while learning about Jesus inside!

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