So, I searched around the Internet to figure out why it reacts this way, and a lot of sites say that it's the gum arabic that is in mentos (and other candies) that causes the surface tension of the water molecules to break easily, which releases more carbon dioxide gas which leads to the eruption. There's a site called
Steve Spangler Science that has a couple of videos showing the mentos in different kinds of soda, and guess what? It appears that mentos do not react stronger in diet coke than in other sodas. Diet coke started being used more because it's easier (not as sticky) to clean up. The tricky part is getting the mentos into the bottle at the same time. In our first bottle of soda, we used a small tube and placed about a roll of mentos in the soda and the results were spectacular. In the remaining bottles we used a larger tube and I believe they tried to put more mentos in (the whole philosophy that more is better) and while the results were still uber-cool, they didn't reach anywhere near the height of the first one, which leads me to believe that we didn't get them in at the same time. Another website said that using plain carbonated water was really impressive. And yet another site said that carefully putting several sugar packets into a 2 liter bottle (which will fizz a little) and then shaking it up will give you a weapon of mass eruption.
I really think more experimentation is needed! I wish my biology class was this exciting.
Heidi