Why Does Mentos in Diet Coke Cause an Eruption?

Today I was searching for information on the new Diet Coke cans. I have had 2 that wouldn't open since they changed to the new design (the aluminum feels flimsier too). The pull tab doesn't work - it doesn't displace the pop top when it is pulled. If anyone can enlighten me as to why this has happened twice in the past week, but never before that that would be something new learned.

My search for answers to this led me somehow to the diet soda and Mentos eruptions. I have tried this at home, and yes, a 2 liter bottle of diet soda will erupt in a tall fizzy column if you drop a few Mentos in.



This is apparently a physical reaction, not a chemical reaction. It all has to do with carbon dioxide bubbles and the way they grow.

Carbon dioxide is added to beverages to make them fizzy. The CO₂ molecules are separate and are held that way by the water in the soda. When a soda is opened the sound you hear and the bubbles you see are CO₂ molecules floating fuzzily to the top. CO₂ molecules would rather hang with other CO₂ molecules and Mentos have a porous surface that allows the CO₂ molecules to gather with others and form bubbles. Since the candies sink quickly to the bottom of the soda bottle the gathering of the CO₂ molecules on the Mentos starts at the bottom and then surges to the top causing the diet soda geysers.

Note: The reason for using diet soda instead of regular corn syrupy soda seems to be that because diet soda is not sticky so any mess made with this experiment is easier to clean up.  If you plan to try this, I highly recommend doing it oustside and away from people, pets, and anything else you don't want to have a soda shower.

Something else I learned: Aluminum forms an oxide coating which is highly resistant to corrosion.