Wednesday, February 9, 2011

Homeschool Science: Mentos Takes the Gas out of Soda

This would be a more relevant experiment for children who drink soda. It would help them contextualize the science behind the sensations that they experience when they drink soda, and aid them in internalizing that the laws of science lie underneath even the smallest aspects of our lives.

My girls don't have much experience with carbonated beverages, but we still find ourselves performing this experiment at least weekly, simply because it's cool.

So the idea behind the Mentos and Coke experiment is that soda contains carbon dioxide gas, and Mentos releases that carbon. Mentos has lots of teeny-tiny little pits on its surface, something that I think that we could see on our pocket microscope (I'm not completely sure if that's what we saw, or if it was artifacts from the light source + shiny candy surface). The teeny-tiny little pits have teeny-tiny little air bubbles in them. It's exposure to air--sort of--that releases the carbon dioxide from the soda. Really, since more carbon dioxide is dissolved in the soda than the soda can support in typical atmospheric conditions, it doesn't take much to make the carbon dioxide escape, and so although Mentos isn't much, it is enough.

Mentos drops into the soda, the nucleation points (those teeny-tiny little pits) attract the carbon dioxide, and the carbon dioxide gas goes up while the Mentos fall down, crossing the entire depth of the soda. Add six more Mentos to multiply the effect, and you're in business.

We've done this experiment before by just dropping the Mentos into the two-liter bottle of diet soda (sugar-free=less sticky), but because the effect occurs so quickly, the person who did the dropping was far too busy running away from the spew to actually observe it. I finally sprang for the depth-charge tube from Steve Spangler Science, which our big-box craft store stocked, in preparation for science fair season, I suppose--and I could use my 40%-off coupon!

The depth-charge tube sports a trigger pin system, and that was all it took to convince Sydney, who'd watched the previous experiments from the safety of the house, to actually come outside and run the experiment herself (this video is a little loud, because I'm shouting across the street to Sydney, but I'm about a foot away from the video recorder):

The passerby, whom I didn't notice at the time, is actually my next-door neighbor taking a walk, and just after this experiment she came over and basically asked, "Why are you always doing crazy stuff outside your house?" It turns out that she, too, used to homeschool!

It's a small, small, awesome and small world.

3 comments:

Meg Nickless said...

It would work with carbonated water, too, I think. Maybe that would be something your kids could take a sip of to experience the bubbly-ness.

Stephanie said...

We like that one, too.
Except, dang! one bottle of pop per explosion gets expensive!!

julie said...

I think we've managed to find the cheapest off-brand soda ever sold, so for me it's the purchasing of the Mentos that's getting old.

We'll def try carbonated water. It'll be fun to expand the experiment!

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