Mentos Geyser Science Project

How to Turn the Mentos Geyser into a Great Science Project

You might be thinking to yourself, “Can I use the Mentos Geyser for my upcoming science fair project in school?” The answer is YES, but you’ll need to learn how to turn a cool science activity into a real science experiment. The secret is to turn your attention away from the spraying soda and concentrate on setting up an experiment where you isolate a single variable and observe the results. Tests and trials will lead you to more and more questions, which will eventually lead to a discovery. The examples below are a good place to start, but you’ll stumble upon even more questions and ideas once you get rolling.

Experiment Materials

  • Several rolls of Mentos chewy mints
  • Several 2-liter bottles of soda
  • Mentos Geyser Tube
  • Video camera


The Fairness Factor

Before the invention of the Geyser Tube, everyone had a different method for dropping Mentos into the bottle of soda. You might have used the test tube method while someone else made a tube out of notebook paper. Unfortunately, the method for dropping the Mentos was never consistent. The Geyser Tube removes the inconsistency because it makes the drop the same every time, letting you focus on the true variables (what you’re trying to test).

The Scale

To make any of these tests meaningful, you need to find a way to measure the explosion. A friend or parent with a video camera is a great way to watch and document the results of your experiment, but you’ll also need some specific measurements or data. Try placing the soda bottle next to the wall of a brick building (after getting permission from the building’s owner). Measure the height of the explosion by the number of bricks that are wet once the geyser stops. If you want a more specific measurement, use chalk to mark off 1-foot increments on the brick wall before you drop the Mentos into the bottle of soda. Make comparisons, create a chart with your data, and draw some conclusions. Be sure to thank the building’s owner and to hose off the wall of the building when you are finished!

If you want to examine the volume of the explosion instead of the height, make note of the volume of a full bottle of soda (2 liters) before you drop the Mentos into it. Once the geyser stops, pour out the remaining contents of the bottle and measure how much liquid is left. You’ll have to find a way to measure in liters. Remember that 1 L is equivalent to 1000 mL. Subtract the remaining amount of liquid from the original volume of the bottle to calculate the volume of the explosion. Then make comparisons, create a chart with your data, and draw some conclusions.

You might want to enlist the help of an adult who owns a camcorder. By recording every launch, you’ll be able to replay the footage of the explosion in slow motion in order to get the best measurement possible.

How Many Mentos?

It’s a question that everyone who does this project asks… What is the best number of Mentos to use to make the highest shooting geyser? In science project terms, “What is the effect of the number of Mentos on the height of the geyser?” This is a great topic for a science fair project, but you’ll need lots of soda and Mentos and a few friends to help record all of the data.

Be sure that the soda bottles are all the same brand and type (diet vs. regular) and are at the same temperature. Use the Geyser Tube to make sure every launch is the same. You want the conditions to be as standardized as possible.

Attach the Geyser Tube to the top of the 2-liter bottle of soda. Push the trigger pin through the holes and load one Mentos into the tube. Remove the top cap of the Geyser Tube – this makes it easier to record how high the soda goes because it’s not spraying everywhere. The column of soda is bigger and stays together better when the cap is not in place. The launch site is ready… the Mentos is loaded… the video camera is recording… now pull the pin! Record the height (at least your best guess for right now). Repeat this same procedure for 2 Mentos, 3 Mentos… you get the idea. Based on your data, how many Mentos do you need to make the highest shooting soda geyser?

The Brand Test

You guessed it… it’s time to put your favorite soda to the test. Does one brand produce higher flying geysers? How does generic soda stack up against the big name brands? In scientific terms, “What is the effect of the brand of soda on the height of the geyser?” Using the procedure outlined above, it’s easy to determine the clear winner. Remember, it’s important to conduct each test the same way using the Geyser Tube and the same number of Mentos for each launch. You’ll also want to make sure all of the soda is at the same temperature because temperature plays an important role in the reaction. The brand of soda is the only thing that changes (the variable).

Just think… your results could help determine the next Mentos Geyser craze!

The Temperature Test

What is the effect of temperature on the height of the geyser? Does warm soda shoot up higher than cold soda? The key is to keep every launch fair and to make sure the only variable is the temperature of the soda. You’ll need a thermometer to record the temperature of the soda just before you launch it.

It’s best to stick with one brand of soda for the entire test. Let’s use Diet Coke. You’ll want to purchase three bottles of Diet Coke and several rolls of Mentos. You’re going to set up three tests – warm soda, room temperature soda, and cold soda. Place one bottle of Diet Coke in the refrigerator and let it sit overnight. Place the second bottle in a place where it can reach room temperature overnight. There are two safe ways to warm the other bottle of soda. The simplest method is to let the unopened bottle sit in the sun for several hours. You can also place the bottle of unopened soda in a bucket of warm water. Never use a stove or microwave to heat a bottle of soda.

It’s time to return to your launching site. Check to make sure your measuring scale is in place and the video camera is ready to roll. Let’s start with the bottle of cold Diet Coke. Open the bottle and dip the thermometer down into the soda. Record the temperature on your data table. Attach the Geyser Tube with the trigger pin in place. Load seven Mentos into the tube and get ready to launch. Keep the cap of the Geyser Tube off. Pull the pin and record the data. Repeat the same procedure for the bottle of soda at room temperature and the bottle of warm soda.

How Does It Work?

Why do Mentos turn ordinary bottles of diet soda into geysers of fun? The answer is a little more complicated than you might think. Let’s start with the soda…

Soda pop is made of sugar or artificial sweetener, flavoring, water, and preservatives. The thing that makes soda bubbly is invisible carbon dioxide, which is pumped into bottles at the bottling factory using lots of pressure. If you shake a bottle or can of soda, some of the gas comes out of the solution and the bubbles cling to the inside walls of the container. When you open the container, the bubbles quickly rise to the top pushing the liquid out of the way. In other words, liquid sprays everywhere.

Each Mentos candy has thousands of tiny pits all over the surface. These tiny pits are called nucleation sites – perfect places for carbon dioxide bubbles to form. As soon as the Mentos hit the soda, bubbles form all over the surface of the candy. Couple this with the fact that the Mentos candies are heavy and sink to the bottom of the bottle and you’ve got a double-whammy. When all this gas is released, it literally pushes all of the liquid up and out of the bottle in an incredible soda blast.

Warm soda tends to fizz much more than cold soda. Why? The answer lies in the solubility of gases in liquids. The warmer the liquid, the less gas can be dissolved in that liquid. The colder the liquid, the more gas can be dissolved in that liquid. This is because as the liquid is heated, the gas within that liquid is also heated, causing the gas molecules to move faster and faster. As the molecules move faster, they diffuse out of the liquid, leaving less gas dissolved in that liquid. In colder liquids the gas molecules move very slowly, causing them to diffuse out of the solution much more slowly. More gas tends to stay in solution when the liquid is cold. This is why at the bottling plant carbon dioxide is pumped into the cans or bottles when the fluid is very cold—around 35 degrees Fahrenheit. This low temperature allows the maximum amount of carbon dioxide to dissolve in the soda, keeping the carbonation levels as high as possible.

Additional Info

Science Fair Connection

The Mentos Geyser Science Project is an excellent example of a science fair project because it clearly shows how to isolate a variable (the thing that changes in the experiment) and standardize all other conditions so that you can see the true effect of the variable on the geyser reaction. You know that dropping Mentos into Diet Coke causes a geyser to erupt. That is a fun demonstration, but it isn’t a science fair project. A true science fair project changes a variable, creates a new experiment, and then compares results.

Purchase our Geyser Tube – and have fun experimenting!

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