- One pack of mint Mentos
- One two-liter bottle of Diet Coke
- Paper tube made by rolling a half-sheet of paper loosely around the Mentos roll and securing with tape – or you can just use the Mentos label
- Index card or other piece of thin cardboard
- Measuring tape
- Towels, water (to clean up)
Before You Begin
This is going to be messy. I strongly recommend that you perform this experiment outside. If you can’t go outside, you can do it in the bathtub or shower using only one or two Mentos. You can also use soda water in place of Diet Coke. The fountain won’t be as high, but it will be easier to clean up! Make sure you have plenty of water on hand to rinse down the area after your experiment.
- Slowly open the 2 liter bottle of Diet Coke.
- Load the paper tube with four Mentos.
- Place the index card over one end of the tube and invert it.
- Set the card and the tube with the Mentos inside on top of the open mouth of the bottle, making sure the opening of the tube lines up with the mouth of the bottle.
- Quickly remove the index card, allowing the Mentos to drop into the bottle
- Step back quickly!
- Record the height of the geyser
- Optional: repeat using a new bottle of Diet Coke and more Mentos – how high can you go?
- Enter your data on the spreadsheet provided. Once we have data for the entire class, we will do some statistical analysis on our results.
- Determining the height can be a little tricky in the moment. It helps to have two people – one to load the bottle, and one to observe. Or set up a video camera and record your experiment so you can estimate the height after the fact.
- If you can, the best way to determine fountain height is to make markers at one-foot intervals on a wall, tree, or pole (see green tape markers on garage door in image below). You can use masking tape or chalk to make the marks. This is easier than trying to hold up a measuring tape.
- Or, you can use a person of known height for a reference. Was the geyser waist-high? Chest-high? Above the head?
- It’s best to put the bottle on a flat surface if possible so it doesn’t tip over.
- Make sure the Mentos can fall freely from the tube before you begin. If the tube is wet or crushed, the Mentos can get stuck inside. If this happens, make a new tube.
- Try not to shake the bottle before you open it, or you will lose some CO2 before the experiment begins. Also, it’s difficult to get the Mentos to go down into a bottle that’s already foaming over.
Just for Fun
If you have someone to help you (or a trusty tripod), record a video of your eruption and turn it in! I’ll make a compilation of “greatest hits” for the website.
Video: Diet Coke & Mentos | MythBusters (1:57)
Video: Science of Mentos - Diet Coke explosions explained (1:26)
Video: Original Mentos Diet Coke Geyser - Cool Science Experiment (2:13)
A bottle of soda contains dissolved carbon dioxide (CO2) under pressure. When you remove the lid, the pressure is released, and the CO2 exsolves in the form of tiny bubbles. When exsolution occurs faster than the gas can escape, the soda gets whipped up into a foam that quickly overflows the confined volume of the bottle – if you have ever shaken or dropped a bottle of soda before opening it, you have probably observed this effect yourself. In this experiment, the Mentos encourage the rapid formation of bubbles by providing a nucleation site. In the absence of a nucleation site, the CO2 gas must overcome the surface tension of the liquid before it can form a bubble, which inhibits the process a bit, especially at the beginning. Mint-flavored Mentos have a pitted surface with lots of surface area, which provides plenty of nucleation sites for bubble growth. The more Mentos, the more nucleation – hence, a soda eruption! It is less clear why Diet Coke works better than regular Coke, but based on observation this seems to be the case. Some people have suggested a chemical reaction involving the artificial sweeteners. However, any carbonated beverage will produce a fountain when Mentos are added, some will just be more dramatic than others. Incidentally, fruit-flavored Mentos do not produce an eruption. This is because they have a smooth waxy coating that does not provide nucleation sites for bubble formation.
Download the Excel Spreadsheet to enter your experimental results
Download and complete the Worksheet for Lab 2: Degassing
You will need to submit the results spreadsheet and the complete worksheet to the Module 2 Lab Assignment in Canvas.