Observations and results
Was the eruption higher when whole Mentos candies were used compared with crushed candies? Was less Diet Coke left in the bottle after the reaction with the whole candies compared with the crushed ones?

In the Diet Coke bottle the Mentos candy provides a rough surface that allows the bonds between the carbon dioxide gas and water to break more easily, helping to create carbon dioxide bubbles. As the Mentos candy sinks in the bottle, the candy causes the production of more and more carbon dioxide bubbles, and the rising bubbles react with carbon dioxide that is still dissolved in the soda to cause more carbon dioxide to be freed and create even more bubbles, resulting in the eruption. Because Mentos candies are rather dense, they sink rapidly through the liquid, causing a fast, large eruption. The crushed Mentos candies, however, are not as dense as the whole ones, which causes them to sink more slowly, creating a relatively small cola fountain, which should also leave more liquid in the bottle than the larger eruption with whole Mentos candies did.

Cleanup
Hose off any part of a building that was splashed with Diet Coke. If you try this project with regular Coke, the eruption should still happen but its sugary content may make cleaning more difficult.

More to explore
Physicists Explain Mentos–Soda Spray from Scientific American
Science of Mentos–Diet Coke explosions explained from New Scientist
The Science of Coke and Mentos from EepyBird.com
Why do Mentos mints foam when you drop them into soda pop? from General Chemistry Online
Coke® & Mentos®—Nucleation Goes Nuclear! from Science Buddies

This activity brought to you in partnership with Science Buddies

3 Comments

1. 1. afiedler 11:09 PM 6/15/12

   "comparing whole with crushed Mentos, the latter of which are less dense." Do you mean the density is not consistent throughout the Mento and some parts may be more dense than others? I wouldn't want students to become confused about the difference between extensive and intensive properties of matter. The density of a smaller piece of a substance is equal to the density of a larger piece.

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2. 2. stevensod 03:00 AM 6/16/12

   Mythbusters looked at this a while back and found that nature of the surface was not the driver of the eruption. Instead it was down to the presence of three ingredients including aspartame and benzoic acid used to flavour the coke. Big eruptions only occurred when aspartame, benzoid acid and caffeine were present in the soda. Otherwise all you got was a gentle froth over.

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3. 3. stefanharjes 04:12 PM 6/26/12

   I think it is highly unlikely that the rough surface
   catalyses carbon dioxide water bond braking. I would guess the surface promotes bubble nucleation/growth.

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