Mentos react with soda because their rough surface lets dissolved carbon dioxide escape fast, creating a geyser.
The reaction
Mentos have a rough, pitted surface that gives carbon dioxide bubbles many nucleation sites to form. The gas escapes quickly and shoots a geyser.
Other factors
- Mentos sink fast.
- Gum arabic lowers surface tension.
- Diet soda gives a bigger reaction (aspartame and potassium benzoate).
Not a chemical reaction
It is physical.
Safety
Do it outside. Never swallow both together.
Experiment variables researchers tested
In the 2008 American Journal of Physics study, Tonya Coffey tested candy surface roughness, candy sinking rate and soda type. She found that the rapid release of CO2 relies on nucleation sites on the rough candy coating. Sugar-free and sugar-coated candies behaved differently, and the dissolved ingredients had effects secondary to the surface.
- Diet soda gave higher eruptions than regular in repeated tests.
- Soda at room temperature gave bigger eruptions than refrigerated soda because gas is less soluble at higher temperatures.
- Candy that sinks faster gives a bigger reaction because it spends more time in the liquid releasing gas.
- Gum arabic in the candy coating and gelatin help reduce surface tension.
Classroom safety
Use goggles, an open outdoor space and a trigger (such as a tube with a card) to drop candies together. The reaction is not chemical, so it cannot be used to make a hazardous substance, but soda can spray into eyes. Clean up sticky residue because it attracts insects. Do not ingest the fizz during the experiment.
Experiment variables
Studies and classroom tests found that diet soda gives bigger geysers than regular soda, mint Mentos outperform other candies because their rough surface provides more nucleation sites, and warm soda reacts more strongly. Coffey’s 2008 paper identified surface roughness and the lower surface tension from aspartame as key factors.
Safety
Do it outdoors, wear eye protection and keep distance. The reaction is physical, not chemical. It does not make candy or soda unsafe, but eating large amounts together can cause stomach upset.
Experiments and results
Researchers have tested over a dozen candies. Mint Mentos in diet soda produced the largest fountains. Rock salt and Wint-O-Green Life Savers also work. Warm soda produces taller geysers since gas is less soluble at higher temperature, and a tall narrow container increases height.
Classroom use
The demo is used to teach nucleation and gas solubility. A 2 liter bottle holds about 6 grams of CO2 per liter of soda. Always use eye protection, a clear outdoor area and do not use glass bottles.
Based on data from the American Journal of Physics and the American Chemical Society
