We added Mentos to a bottle of coke and watched it explode. We learnt that a bottle of coke is full of carbon dioxide. When you drop any sort of object into a bottle of soda, bubbles form on the surface of the object. The Mentos drop to the bottom of the bottle, forming lots of bubbles on its textured surface. When all of this gas is released it forces the liquid up and out of the bottle in a giant eruption.