Hosts: Mignon Fogarty and Adam Lowe
Transcript: This episode originally aired July 27, 2006
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What causes the geyser?
Will from SmartBombRadio asks: "I've seen videos on the Internet and on YouTube of people dropping containers of mentos into warm diet coke bottles. The resulting geyser of coke reaches 10-12 feet in the air. I've repeated this, and it works. My question, why does this happen?"
So what Will is talking about is that if you drop Mentos into a liter bottle of soda like Diet Coke it will instantly create a huge geyser of pop shooting out of the bottle. Mentos is a type of candy for those who don't know, I don't know if they have Mentos everywhere in the world where we have listeners. And there's videos of this on YouTube and we put one in our blog at welltopia.com. The videos are amazing, it looks like soda shoots up as much as 30 feet.
So what causes the instant geyser?
Well, my first thought was that it must be like making a baking soda volcano, where you make a big geyser from the chemical reaction that happens when you mix baking soda (which is a base) with vinegar (which is an acid) and create a bunch of carbon dioxide.
But Mentos actually aren't basic, and experts say that the Mentos/Diet Coke geyser is actually the result of a physical reaction. What happens is that soda is already pumped full of carbon dioxide, which is why sometimes you'll hear it called a carbonated drink. The strength of the bonds between the water molecules in the soda keep the tiny carbon dioxide bubbles in solution. That's called surface tension. There are some really cool pictures on Wikipedia of surface tension in action, like a penny floating on top of a glass of water.
Now dropping any sizable object into the soda will at least slightly break that surface tension, and you can see that by the tiny bubbles that will quickly form on the object. Like if you drop a penny into soda carbon dioxide bubbles will immediately appear on it.
Well, it turns out that Mentos are just really good at breaking that surface tension because they are heavy enough to sink all the way to the bottom quickly, and they have lots of tiny imperfections on their surface that serve as nucleating sites for the carbon dioxide bubbles. When those bubbles form they push the soda up and out of the narrow opening at the top of the bottle. And also, they contain coconut oil and an ingredient called gum arabic, which is an oily gum, both of which make it even easier for the carbon dioxide bubbles to get free because oil and water don't mix. This makes the water molecules in the matrix more attracted to each other because they are repelled by the oil, and so again, it takes less energy for the carbon dioxide to break free.
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Also, the articles I found said it is safe to eat Mentos and drink soda at the same time. The soda has to be still for there to be surface tension that the Mentos can disrupt, and when you drink soda it is sloshing around in your stomach so there's no surface tension. And I didn't see this anywhere but I'm guessing that the sloshing around in your stomach releases some of the carbon dioxide much like shaking a bottle of soda would do, and that is probably why people often burp after drinking pop.
Nobody seems to really know why, but diet coke seems to work better than regular coke. People speculate that maybe the diet coke has more carbon dioxide in it, but that's just a theory. But diet coke is also a lot less sticky to clean up than regular coke, so if you try this you'll get a better effect and have an easier time cleaning up. Just make sure to have a lot of open space and keep your face away from the opening as you drop the Mentos in, because it shoots up really fast.
