Mentos and soda geyser
01 // Question
How does the number of Mentos dropped into a bottle of soda change the height of the eruption?
A testable question names one thing you change (number of candies) and one thing you measure (eruption height).
02 // Variables
Independent
Number of Mentos candies- 2 candies
- 4 candies
- 6 candies
Dependent
Height of the eruption- Height in inches, measured against a marked backdrop
- Time until the eruption stops
03 // Hypothesis
IF more Mentos candies are dropped into a bottle of soda at once, THEN the eruption will reach a greater height, BECAUSE each candy's rough, pitted surface gives dissolved carbon dioxide more places to rapidly form bubbles, and more candies create more of those release sites at once.
04 // Procedure
1. Set up outdoors
Do this test outside, on a surface that can get wet, with everyone wearing eye protection and standing back.
2. Mark a height scale
Set the soda bottle against a wall or board marked with height lines for measuring the eruption.
3. Load the candies
Load the chosen number of Mentos into a rolled-paper tube or drop tool so they can enter the bottle all at once.
4. Drop and observe
Remove the bottle cap, drop the candies in immediately, and step back to observe the eruption.
5. Record and reset
Record the eruption's peak height, then repeat with a fresh bottle and a different candy count.
05 // Data table
| Number of Mentos | Trial 1 height (in) | Trial 2 height (in) | Average height (in) |
|---|---|---|---|
| 2 candies | ____ | ____ | ____ |
| 4 candies | ____ | ____ | ____ |
| 6 candies | ____ | ____ | ____ |
06 // What to expect
More candies generally produce a taller eruption, because each Mentos adds thousands of tiny rough pits that act as nucleation sites — spots where dissolved carbon dioxide can rapidly form bubbles instead of staying dissolved in the liquid.
This is a physical reaction, not a chemical one — no new substance is created. The soda already contains dissolved CO2 gas; the candies just give it a fast, crowded place to escape all at once.
07 // Lab notes
- Safety. Do this outdoors only, on grass or pavement that can be hosed off, well away from anyone's face.
- Safety. Wear eye protection and stand back immediately after dropping the candies — the eruption starts within a second.
- Diet soda works best, since it leaves less sticky sugar residue to clean up afterward.
08 // Remember
The gas was already in the soda. The candy just gives it thousands of tiny doors to escape through at once.
09 // Questions people ask
Why do Mentos make soda erupt?
It's a physical reaction called nucleation. Soda holds dissolved carbon dioxide gas under pressure. A Mentos candy has a very rough, pitted surface that gives the gas thousands of tiny spots to rapidly form bubbles all at once, releasing the CO2 far faster than it would escape on its own.
Is the Mentos and soda reaction a chemical reaction?
No — it's physical, not chemical. No new substance is produced. The carbon dioxide gas was already dissolved in the soda; the candy's surface simply speeds up how fast that existing gas can form bubbles and escape.
Why does diet soda work better than regular soda for this experiment?
Diet soda is less sticky and easier to clean up, but the eruption mechanism works the same in both. Some people find diet soda's slightly lower viscosity lets bubbles form a bit more easily, though the candy's rough surface is still what drives most of the effect.