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How does this happen? Carbon dioxide is pumped into soda and it wants OUT, as you can see/hear anytime you open a new bottle of soda -that hissing sound is the CO₂ escaping. A piece of Mentos candy has microscopic pits all over it. These are called nucleation sites - places where CO₂bubbles can grab onto. A ton of CO₂ bubbles will form all over each Mentos candy as they sink to the bottom (we put in 8 candies) . The bubbles seed more bubbles as they rise & soon there is a raging foam in the bottle - pressure builds & the result is a huge geyser! Almost all of the soda comes shooting out of the bottle! I do this every year with my students & I never get tired of the looks on their faces - priceless! I use this experiment to teach the scientific method: making observations, asking questions, making hypotheses, recording data, making conclusions. 

         Using this tube has made it much easier for me to get out of the way before the geyser erupts: