1. Mentos and Soda

2. Why does this happen?
There are many different factors that play a part in the Mentos and soda experiment reaction.
They include:
surface tension
Surface area
Supersaturated compounds
Polar attractions
Nucleation sites

3. What makes Mentos so special?
The surface of a Mento is sprayed over, over, and over with microscopic layers of liquid sugar. This makes them sweet and gives the so many numerous nooks and crannies on their surface.
Mentos are also fairly dense, so they sink quite rapidly which creates lots of bubbles.
Mentos have a high ratio of surface area to volume. This causes a low surface tension, which helps bubbles to grow quickly

4. Mentos also contains a substance called gum arabic
Mentos also contains a substance called gum arabic. This substance acts as a surfactant, which further reduces the surface tension in the liquid!
As a point of interest, a rough surfaced mint that did not contain a surfactant would not cause this increased reduction of surface tension and would NOT create such a large fountain!

5. What makes the soda so special?
Sodas are carbonated and carbonated drinks contain carbon dioxide. All of that enclosed carbon dioxide is squeezed into the bottle and trying to get out. The need to be freed causes the CO2 to gravitate to any material or bump it can grab on to. These “bumps” are called nucleation sites. Nucleation sites are places where the CO2 can grab onto and start forming bubbles. A nucleation site can be a scratch in glass or the ridge on your finger. It just needs to be a place where there is a high surface area in a very small volume.

6. Water molecules are very strongly attracted to each other and will collect around a bubble of carbon dioxide in the soda.
For more carbon dioxide bubbles to form they have to break the surface tension of the water molecules.
The gum arabic in the Mentos breaks the surface tension of the water molecules making the carbon dioxide bubbles to form more quickly.
The nucleation sites that are ALL over the candy are the spots where these carbon dioxide bubbles naturally want to gravitate to.

7. Tests have shown that: Caffeine does not accelerate the reaction
Acidity does not change, so it is not an acid-base reaction
Water containing aspartame (the sugar substance in diet sodas) causes the surface tension to be lower. This could be one of the reasons that the reaction works better when using diet sodas.