Sci-Tech Discovery Center at home experiment: Soda Geyser

Carbonated drinks like most sodas are pumped with carbon dioxide to give the drinker the fizz feeling. This gas is suspended within the soda. Any shift in the forces inside can cause these gas molecules to come out of suspension. This effect can be seen when you shake a can. When shaken, the pressure increases as the gas inside tries to expand. When you open the container, this gas will push out to an area of lower pressure (a.k.a. the outside). As it leaves the container, the quick eruption will cause liquid to come out at the same time causing the subsequent spray!

When Mentos are dropped in, the surface tension of the soda is disrupted, allowing bubbles to form. Added to that, Mentos have thousands of microscopic pits that allow bubbles to form. As the bubbles expand, they are released and will push the soda out. In the video below, you can see the effect Mentos has on a bottle of diet coke — how cool is that soda geyser?