How to Make a Mentos & Diet Soda Chemical Volcano Eruption

Chemical volcanoes are classic projects for science fairs and chemistry demonstrations. The ​Mentos and diet soda volcano is similar to the baking soda volcano, except the eruption is really powerful, capable of producing jets of soda several feet high. It's messy, so you might want to do this project outdoors or in a bathroom. It's also non-toxic, so kids can do this project. This simple chemical volcano takes a few minutes to set up and erupts for a few seconds

What You Need

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Mentos and Soda Project

By Anne Marie Helmenstine, Ph.D.

• Roll of Mentos candies
• 2-liter bottle of diet soda
• Index card
• Test tube or sheet of paper
• A mop for cleanup

Making the Mentos and Soda Erupt

1. First, gather your supplies. You can substitute another candy for the Mentos, such as M&Ms or Skittles, but ideally, you want candies that stack into a neat column with minimal space between them, have a chalky consistency, and barely fit through the mouth of a 2-liter bottle.
2. Similarly, you could substitute normal soda for diet soda. The project will work just as well, but the resulting eruption will be sticky. Whatever you use, the beverage has to be carbonated!
3. First, you need to stack the candies. The easiest way to do this is to stack them in a test tube narrow enough to form a single column. Otherwise, you can roll a sheet of paper into a tube just barely wide enough for a stack of candies.
4. Place an index card over the opening of the test tube or end of the paper tube to hold the candies in the container. Invert the test tube.
5. Open your full 2-liter bottle of diet soda. The eruption happens very quickly, so set things up: you want the open bottle/index card/roll of candies so that as soon as you remove the index card, the candies will drop smoothly into the bottle.
6. When you're ready, do it! You can repeat the eruption with the same bottle and another stack of candies. Have fun!

How the Mentos and Diet Soda Experiment Works

The Diet Coke and Mentos geyser is the result of a physical process rather than a chemical reaction. There's a lot of carbon dioxide dissolves in the soda, which gives it its fizz. When you drop a Mentos into the soda, tiny bumps on the candy surface give the carbon dioxide molecules a nucleation site or place to stick. As more and more carbon dioxide molecules accumulate, bubbles form. Mentos candies are heavy enough they sink, so they interact with carbon dioxide all the way to the bottom of the container. The bubbles expand as they rise. The partially dissolved candy is sticky enough to trap the gas, forming a foam. Because there's so much pressure, it all happens very quickly. The narrow opening of a soda bottle funnels the foam to make a geyser.

If you use a nozzle that makes the opening at the top of the bottle even smaller, the jet of liquid will go even higher. You can also experiment using regular Coke (as opposed to the diet versions) or tonic water (which glows blue under a black light).