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Soda Fountain 4.JPG

Soda Fountain

Safety Warning

Reaction causes slippery floor. Caution after doing the experiment.

Soda Fountain 1.JPG


•    Diet soda (Pepsi or Coke)
•    Mentos (any flavor)
•    Basin
•    Test tube (big enough for Mentos)
•    Index card or flat hard cover


  1. Put the soda bottle in the basin.

  2. Empty Mentos candy into the test tube (around 8-10 pcs for a 2L soda).

  3. Remove the bottle cap and cover with an index card.

  4. Place the test tube (with Mentos) upside down over the mouth of the bottle. 

  5. Remove the index card allowing the pieces of Mentos to fall continuously into the bottle.

  6. Step back and watch the reaction!

What's the Science?

This famous reaction is not chemical but physical! It happens for two main reasons, 1) the texture of the candy and; 2) how fast it plummets to the bottle's base.


All the carbon dioxide in the soda (the fizz we hear when we open it), is squeezed into the liquid and looking for a way out. It’s drawn to any tiny bumps that it can grab onto. Those tiny bumps are called nucleation sites: places the gas can grab onto and start forming bubbles. The surface of a piece of Mentos is sprayed with over 40 microscopic layers of liquid sugar. That makes it not only sweet but also covered with lots and lots of nucleation sites.


Since the Mentos candies are also heavy enough to sink, they react with the soda all the way to the bottom. The escaping bubbles quickly turn into raging foam, and the pressure builds dramatically. All that pressure has got to go somewhere, and before you know it, you've got a big geyser happening!


Experiment with different sodas, different carbonated drinks and Mentos flavors to observe different reactions.

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