When making a volcano for a science fair or school project, the combination of baking soda and white vinegar is often used to make that volcano erupt. However, that's not the only way to create an eruption worthy of an "A." A combination of Mentos candies and Diet Coke creates a bubbly eruption that's a nice variation on the original. This technique does require a bit more space, so the volcano should have a large cavity in the centre (such as an orange juice concentrate can or a water bottle). The explosion may also be messier than the traditional method, so this volcano should only be activated outside.
Set up the volcano on a wide, flat surface outside. Cover the area with newspapers if you're concerned about the mess. This combination can get rather sticky.
Insert the tip of a funnel into the volcano's hole and slowly funnel the can of Diet Coke into the hole. The Diet Coke will fizz up, so take your time. You don't have to use the whole can, but pour as much Diet Coke as possible into the cavity.
Align one of the ends of the toilet paper tube with the volcano opening. Drop the Mentos through the tube and into the volcano's hole. The number of Mentos needed depends on how large the hole is and how much Diet Coke is being used, but generally two to four candies will do the trick.
Jump back, bringing the toilet paper tube with you, as soon as the Mentos are immersed in the Diet Coke. The eruption will occur almost immediately and could produce a big spray, depending on how large the volcano cavity is.
Repeat as many times as desired. The eruption shouldn't harm the volcano, so it should be good to go again right away. When finished, wipe the volcano clean with damp paper towels.
If the eruption is sluggish, try stirring the Mentos and Diet Coke with a spoon or rod to activate the volcano.