I mentioned in a previous blog post that Steve Jacobs (consultant for the Discovery Channel) called in May to let me know that Adam Savage and Jamie Hyneman from MythBusters were going to do a segment on the Mentos things. Steve wanted to be able to share what worked well for us and our latest scientific explanation. The MythBusters episode aired last night (Aug 9th) on the Discovery Channel and I was eager to see if they had tried our secret weapon (besides Mentos) – plain old salt. And they did. They mentioned our “unofficial” 18 foot record and even used our giant test tubes as a loading device for the Mentos (cool).
In an effort to uncover the true “science” behind the reaction Adam and Jamie confirmed most everything that we’ve published to date. According to Jamie, the main cause of the reaction between the soda and the candy is one called “nucleation,” in which the particular chemistry of the Mentos candy interacts with the chemistry of the carbonated Diet Coke, causing the carbon dioxide gas, or CO2, to suddenly come out of suspension in the liquid and make a break for freedom.
As expected, Adam and Jamie tried the non-mint variety of Mentos and discovered that they didn’t work well at all. “The non-mint type,” Hyneman says, “have a glaze on them, and they don’t work at all. It only works with the mint ones, because they have a matte finish. That surface serves as these little portals for the gas to escape through.”
According to a story posted at Zap2it.com, Jamie Hyneman says, “There’s a cascade that happens with — it’s a little esoteric — an ion exchange. Basically the Mentos start to dissolve, and it’s like tripping a switch. It’s not what you would call a chain reaction, because that’s something else in chemistry terms, but it’s a cascade whereon all of a sudden, all of the CO2 that was contained in the liquid is suddenly not as attracted to the liquid as it was before, because of this slight change in the chemistry that occurs.”
That’s not surprising, since we all know how a change in chemistry can cause attraction to wane. But as in many things, a little sweetness can slow the process — so regular, sugared soda doesn’t produce the same reaction.
“Sugar molecules are very large,” Hyneman says, “and that doesn’t allow this to happen as quickly. That’s the key. Sugar is gooey and sticky — even though it doesn’t seem that way when it’s in a soda, but there’s a lot in there — and it helps hold onto the CO2 a lot better.”
On the other hand, Hyneman says, sweetness of no kind — natural or artificial — results in a disappointing fizzle.
“In the case of just plain seltzer water,” he says, “which we also tried, that doesn’t work, because the CO2 already wants to come out.”
Mentos, though, isn’t the only thing that can make a satisfying diet-soda geyser.
“Mentos,” Hyneman says, “which is all well and good, and it works quite well, is actually not the best performer in creating this eruption. Plain old table salt is better.”
Hyneman also says it isn’t necessary to use Diet Coke, that any artificially sweetened carbonated soda should work well.
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Click on the Mentos category to find more commentary from some really smart people, some people who aren’t so sure about the whole thing, people who hate this whole phenomenon… and some people who can’t get enough.