Have you tried this with experiment with Mentos and Diet Coke?
It's fun and not harmless!
Stuff you need:
1-pack of Mentos
1-2 Liter Diet Coke
that's it!
Do it in a clear area where you can't make a mess.
Dump 8 mentos into the Diet Coke....and GEISER! 😄
This will give you a better idea: