What happens when you mix Pepsi and Mentos?

Mixing Pepsi and Mentos creates a powerful eruption of soda that reaches several feet high. Diet Pepsi or regular Pepsi produces the same effect, but regular soda causes a stickier effect.

To try this experiment, stack the Mentos in a column using a test tube. Place an index card on top of the test tube to hold the candies in the container. Open a 2-liter bottle of diet soda and place the test tube upside-down over the opening of the bottle. Remove the index card so that the candies drop into the bottle. Leave the area as quickly as possible because an eruption occurs as soon as the Mentos fall into the bottle.