… but I’m not buying it.

The Orlando Sentinel recently ran a article in their Weekend Leisure Playing with Food section by Jane Snow about the Mentos and Diet Coke experiment. They turned to Robert Wolke, chem professor at the University of Pittsburgh for an explanation. Here’s what he writes…

“The scientific explanation is that craggy-surfaced Mentos candies help release the carbon dioxide that is dissolved in the pop. The carbon dioxide normally remains dissolved in the liquid because there are no irregularities around which bubbles can form. Diet Coke works better than regular Coke because it contains no sugar. The corn syrup used in most sodas, says Robert Wolke, chemistry professor at the University of Pittsburgh and author of What Einstein Told His Cook, suppresses the formation of bubbles.”

Hmmm? I’d suggest that Robert Wolke try dropping a roll of Mentos into a bottle of regular Root Beer or Coke or Pepsi. Judging from the stains on the ceiling in the chemistry department at Regis University, I’d have to say that nothing was really suppressed.

What’s your experience with regular soda?

18 replies
  1. Don Lewis
    Don Lewis says:

    FYI regarding the mentos experiment: You are correct that the professor is wrong about the surface induced the mento effect. if you sand off the coating off the mentos and submerge the coating at the bottom of the bottle you still get the violent release of Carbon dioxide. The “sanded” mento is no longer effective. You can try other candies and mints and they do not replicate the mentos effect. We also observed that mentos have a much better effect in 7 up than either diet or regular coke. Diet and non diet drinks are the same.
    There is some sruface chemsitry and we are thinking about emuslifers in the coating.
    Doug Lewis

    Reply
  2. Jamie Bowsher
    Jamie Bowsher says:

    Does anyone think that the Mentos and Coke thing would make a good science fair experiment? Perhaps they could alter the surface of the mints and test to see if it still works?

    Reply
  3. Jan Duane
    Jan Duane says:

    Guys, I’ve been a chemist for over 25 years, and my husband’s an engineer for over 30. We’ve been noodling this around since our daughter did the experiment at school (and saw the Mythbusters’ show, too). All of the discussions about ‘surface area’ and ‘dissolved CO2’ just can’t account for the amount and rapidity of the evolution of CO2.

    If someone wanted to do a controlled experiment to determine whether it is a chemical reaction or just a physical effect (the ‘nucleation/dissolved CO2’ question), here’s a simple way to set it up:

    Use whole Mentos. Then use the same amount of Mentos but ground up small. A surface phenomenon should have a significantly different rate of reaction with the increased surface area – I predict it would cause the soda to almost explode relative to the whole mints.

    Measure the pH of various sodas, and determine if the geyser height is correlated to acidity. I predict a correlation.

    Find out the composition of Mentos. I suspect they are composed in large part of either bicarbonate of soda NaHCO3 or something similar that serves as a source of additional CO2. Unless you do a mass balance and a quantitative assay of the ‘after’ material, you wouldn’t see anything other that the apparent components of the starting materials. (For those of you who may not remember, it is vinegar and sodium bicarbonate that are used to react to create that wonderful ‘volcano’ that you probably made in elementary school.)

    If anyone is willing to take this on, I suspect they could definitely answer the question: chemistry or physics?

    Reply
  4. Steve
    Steve says:

    Jan — Thanks for the post. The MythBusters took a stab at trying to explain the reaction and did a fairly good job. You can see the story at http://www.stevespangler.com/archives/2006/08/10/mythbusters-take-a-stab-at-the-mentos-madness/

    When one of their consultants from the Discovery Channel called us back in May, we suggested using salt because of the incredible surface area. Adam and Jamie did a nice job of trying different components in soda. Just plain soda water (carbonated water) did not do well, but soda water with aspartame (Nutra Sweet) did very well. Soda water with sodium benzoate (a preservative) also shot up high. Soda water with a sugar additive didn’t do as well as the artificial sweetner. Their conclusion was a combination of nucleation sites on the Mentos and the unique chemistry behind Diet Coke.

    However, they didn’t try our most interesting discovery… used Mentos work even better than new ones. Drop a roll of Mentos into the bottle of Diet Coke, enjoy the geyser and quickly retrieve the Mentos in the bottom of the bottle. Drop these “used” Mentos into a new bottle of Diet Coke and the eruption is even better. Why? After looking at the used Mentos up close, you’ll notice even more bumps and pits on the surface of the candy, providing more nucleation sites for the bubbles to form.

    Who would have ever thought that this crazy reaction that we started playing with back in 1998 would stir up this much interest?

    Reply
  5. polly
    polly says:

    Just a little heads up to some of the teachers and parents out there. I recently found out that a couple of my students have been trying these reactions in vivo as pranks and dares.

    The story I got was that one of them ate 3 mentos, then was going to “chug” a can of diet coke, didn’t finish the can and basically vomited foam from the mouth for a considerable amount of time.

    Reply
  6. Jim
    Jim says:

    Jan, is the surface phenomenon you are talking about nucleation sites or decreasing surface tension? how would you tell the difference?

    What would be the explanation for a link of the intensity of the reaction to pH?

    Can anyone help me understand… JBM

    Reply
  7. Jacy
    Jacy says:

    My friends and I are doing this project,but our question is which soda can make the mentos go higher?
    We learned that the mentos’ surface has tiny holes which let the CO2 in and it causes it to become heavy and fall.Followed by bubbles.The bubbles cause the mentos to shoot in the air folllowed by the soda explosionn.I basically understand this experiment,but I cannot word it out correctly.

    Reply
  8. Dee
    Dee says:

    My son is doing this experiment for his science fair project; Mint vs Fruit, Coke vs Diet Coke vs Sprite etc., however, I think the coating may have changed, the fruit and mint mentos seem to have the same texture. Is the maker of Mentos messing with science by changing the coating?

    btw, for the sake of my sanity we only used 16 ounce bottles and dropped 2 mentos in each. Still a decent eruption, but not one I needed to scrape off the ceiling.

    Reply
  9. Navodit
    Navodit says:

    hay, mintose containing some type of mints(a natural terpenoids like camphor,menthol….),they generally not very soluble in water, but once in solution they reduce surface tension very rapidly.Porous structure of mintose help to disolve mint rapidly due their larger area of contact.Now the physicochemical character of this mixture(mintose + coke) is very much recemble to shanpange!!!!!!!!!!!!!

    But why not normal coke??????
    the sugar molecules of the coke makes hydrogen bond with water & reduce solubility of mints(they got small no of free water molecule to form hydrogen bond in order to disolve)thus surface tension is not much reduced…………

    Reply

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