Super Soda Geyser


Experiment Procedure

  1. Open the Geyser Tube by pulling the pin on the side out.
  2. Insert about 6 Mentos into the tube. Push the pin back into the Geyser Tube to prevent the Mentos from falling out, and flip it over.
  3. Open one soda bottle.
  4. Carefully screw the Geyser Tube onto the soda bottle. Double check that your pin is all the way in, or else your Mentos might fall in and give you a surprise soda shower.
  5. Get ready to run away… pull the pin out to release the Mentos, stand back, and watch it blast off! Reuse the Mentos and try out the different shaped caps in your kit to see which one goes highest.
  6. Rinse and dry your Geyser Tube, and unscrew the red cap.
  7. Make sure the pin is at the “in” position. Load the Depth Charge with the rock salt.
  8. Carefully slide the 
loaded Depth Charge, open end up, into the Geyser Tube. Screw the nozzle back on the Geyser Tube.
  9. Screw the Geyser Tube onto another soda bottle.
  10. You know the drill: get ready, pull the pin, and run away while the geyser erupts!

Materials List

  • Geyser Tube
  • 2 Soda Bottles
  • Table Salt
  • Rock Salt
  • Depth Charge
  • Mentos Roll
  • Adult supervision

How Does It Work?

Here’s the question of the day… Why do Mentos and soda produce this incredible eruption? While we offer the most probable explanations below, there is considerable debate over how and why this works. We also understand and admit that other explanations could be possible.

The thing that makes soda bubbly is carbon dioxide gas. Until you open the bottle, the gas mostly stays suspended in the liquid and cannot expand to form more bubbles, which gases naturally do. If you shake the bottle and then open it, the gas is released from the protective hold of the water molecules and escapes, taking some of the soda along with it.

Water molecules strongly attract each other, linking together to form a tight mesh around each bubble of carbon dioxide gas in the soda. In order to form a new bubble, or even to expand a bubble that has already formed, water molecules must push away from each other. It takes extra energy to break this “surface tension.”

When Mentos are dropped into soda, the gelatin and gum arabic from the dissolving candy break the surface tension. This disrupts the water mesh. Each Mentos candy has thousands of tiny pits all over its surface called nucleation sites – perfect places for carbon dioxide bubbles to form. As soon as the Mentos hit the soda, bubbles form all over the surface of the candy, the Mentos sink to the bottom, gas is released, and it pushes all the liquid up and out of the bottle in an incredible soda blast!

The Depth Charge was specially designed to allow you to test how well other materials work when it comes to creating a soda geyser. It’s tough to test how well table salt works if there’s not a good (and consistent) way to drop it into the soda. With the Depth Charge, it is possible to really conduct tests under scientific conditions.

You probably noticed the small weight on the end of the Depth Charge. This causes it to drop quickly to the bottom of the soda bottle. When the Depth Charge hits the bottom, the two sides split apart and release the material (whatever you picked for your Geyser Starter) into the soda. It’s important to get the starter material to the bottom of the bottle as quickly as possible to get the greatest geyser effect. Also remember that the secret is to select a Geyser Starter that has a rough surface – a place for carbon dioxide bubbles to collect and finally escape. Filling the Depth Charge with smooth marbles will produce no geyser while tiny particles of sand or rock salt produces great geysers.

Science Fair Connection

Observing and using the Super Soda Geyser is pretty cool, but this activity isn’t a science fair project, yet. You can make it one simply by identifying a variable (something that might change the outcome) in the experiment, then testing that variable, and correctly reporting the results. Think about some variables like these that you might test:

      • Try altering the type of soda you use. Make sure you keep all other variables the same, including the temperature of the soda!
      • Try using a different material in the Depth Charge instead of the rock salt.

These are just a couple of ideas, but you aren’t limited to them! Come up with different ideas of variables to test and give them a try. Remember, you can only change one variable at a time for each test. For example, if you are testing different water temperatures, make sure that all other factors in the test remain the same!