Mentos Geyser Experiment - Cover Image

Mentos Geyser Experiment Steve Spangler Science

Drop Mentos into a bottle of soda and run away from the 20 foot geyser

Mentos Geyser Experiment at Steve Spangler Science

What do you get when you mix Mentos and Coke? Follow our step-by-step instructions in our Mentos Geyser Experiment and find out! Drop your Mentos into a bottle of diet soda and run! Beware of the 20-foot (or higher!) geyser that will occur. Why does reaction happen? What is it with this experiment with soda and Mentos that causes this explosion to shoot so far into the air?

Mentos and Coke Experiment

The Mentos Geyser Experiment has been called the “vinegar and baking soda” reaction for a new generation. While science teachers have been dropping candies and mints into 2-liter bottles of soda for years in an effort to release all of the dissolved carbon dioxide, the Mentos and Diet Coke reaction became world famous in 2005. Fueled by hundreds of blogs and popular online sharing sites like YouTube, this once-obscure Mentos and Coke reaction quickly became an internet sensation. The enthusiasm for dropping Mentos mints into soda bottles still continues to grow today. Once you get past the initial “gee-whiz” factor, there’s some amazing science behind the super-cool reaction between a simple carbonated beverage and a chewy mint!

Experiment Materials

    No Products

  • A roll or box of Mentos chewy mints (stick with the standard mint flavor for now)
  • 2-liter bottle of diet soda (either diet or regular soda will work for this experiment, but diet soda is not sticky when you’re cleaning it up, and it will usually create a bigger blast)
  • Sheet of paper to roll into a tube
  • Steve Spangler’s Geyser Tube toy (optional . . . but highly recommended!)

Experiment Videos

Experiment

1

This activity is probably best done outside in the middle of an abandoned field or on a huge lawn.

2

Carefully open the bottle of diet soda. Again, the choice of diet over regular soda is purely a preference based on the fact that erupting regular soda becomes a sticky mess to clean up because it contains sugar. Diet soda uses artificial sweeteners instead of sugar, and consequently, it’s not sticky. Later on in the experiment, you’ll be invited to compare the geyser power of diet versus regular soda, but for now we’ll start with a 2-liter bottle of diet soda.

3

Position the bottle on the ground so that it will not tip over.

4

Let’s start with seven Mentos for our first attempt. The goal is to drop all seven Mentos into the bottle of soda at the same time (which is trickier than you might think). One method for doing this is to roll a piece of paper into a tube just big enough to hold the loose Mentos. Other methods include using a large plastic test tube to hold the Mentos or using my Geyser Tube toy invention, which was created to solve this very problem. Assuming that you’re using the paper tube method, you’ll want to load the seven Mentos into the tube, cover the bottom of the tube with your finger, and position the tube directly over the mouth of the bottle. When you pull your finger out of the way, all seven Mentos should fall into the bottle at the same time.

5

Enough waiting . . . this anticipation is killing me. 3-2-1 drop the Mentos!

6

This final step is very important . . . run away! But don’t forget to look back at the amazing eruption of soda.

7

If spectators were watching your exploits, someone is bound to yell out, “Do it again!” and that’s exactly what you’re going to do.

How Does It Work

Geysers of Fun

Why do Mentos mints 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 (CO2), which is pumped into bottles at the bottling factory using lots and 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 (thanks to tiny pits and imperfections on the inside surface of the bottle called “nucleation sites”). When you open the container, the bubbles quickly rise to the top, pushing the liquid out of the way. In other words, the liquid sprays everywhere.

More Carbon Dioxide Observations

Is there another way for the CO2 to escape? Try this: Drop an object (like a raisin or a piece of uncooked pasta) into a glass of soda. Notice how bubbles immediately form on the surface of the object. These are CO2 bubbles leaving the soda and attaching themselves to the object. Adding salt to soda also causes it to foam up. That’s because thousands of little bubbles form on the surface of each grain of salt. This bubbling process is called “nucleation.” The places where the bubbles form — whether on the sides of the can, on an object or around a tiny grain of salt — are called the (yep, you guessed it!) nucleation sites.

Why are Mentos Mints so Special?

The reason why Mentos work so well is twofold. First, there are thousands of tiny pits on the surface of each mint. Second, the weight of the Mentos candy itself is important in this Mentos and Coke experiment. Each Mentos mint has thousands of tiny pits all over its surface. These tiny pits act as those nucleation sites we discussed — which are perfect places for all those CO2 bubbles to form. As soon as the Mentos mint hits the soda, bubbles form all over the surfaces of the candies and then quickly rise to the surface of the liquid. Couple this reaction with the fact that the Mentos candies are heavy and sink to the bottom of the bottle and you’ve got a double whammy! The gas released by the Mentos mints literally pushes all of the liquid up and out of the bottle in an incredible and amazing soda blast! Cool, huh?

Measuring the Height of the Geyser

To make any of these tests meaningful, you’ll need to find a way to measure the height of the eruption in this experiment with soda and Mentos. Have a friend or a parent record this experiment while you perform it. This is a great way to watch and document the results of your experiment; however, you’ll also need some specific measurements for data. Try placing the soda bottle next to the wall of a brick building (after getting permission from the building’s owner, of course). Measure the height of the geyser by counting 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!

 

Measuring the Volume of the Geyser

If you want to examine the volume of the geyser instead of the height, make a note of the volume of a full bottle of soda before you drop the Mentos into it. (OK, this is a trick question because a 2-liter bottle of soda holds — you guessed it — 2 liters!) Once the geyser stops, pour out the remaining contents of the bottle and measure how much liquid is left inside. You could use a beaker or a graduated cylinder to measure the remaining liquid in milliliters. Remember that 1 liter is equivalent to 1000 mL. Subtract the remaining amount of liquid from the original volume of the bottle to calculate the volume of the geyser. Then, make comparisons, create a chart with your data and draw your conclusions.

How Many Mentos Work Best?

This has to be the number one question that everyone asks about this experiment with soda and Mentos. What exactly IS the best number of Mentos mints to use to make the highest-shooting geyser? This is a great topic for a science project — you’ll need lots of soda and Mentos mints and a few friends to help record all of the data.

Be sure that the soda bottles are all the same brand and type. It’s also important that all of the test bottles are stored in the same place so that the liquid in each bottle is the same temperature.

Line up a row of ten 2-liter bottles against a brick wall (see “Measuring the Height of the Geyser”). Each bottle will receive a different number of Mentos. Drop one Mentos candy into the first bottle and record the height by counting the wet bricks (or set up your own scale behind each soda bottle). Drop two Mentos candies into the second bottle — and so on — until you’ve completed the experiment with all ten bottles.

Of course, this could go on forever. However, you’ll start to see a trend in your data that shows the maximum height of the geyser for a certain number of Mentos. Many soda geyser-ologists believe that seven Mentos candies produce the highest-shooting geyser. Using any more than seven Mentos mints is just a waste, according to these soda-soaked science enthusiasts. What do your results reveal about the effect of the number of Mentos on the height of the geyser?

The Brand Test

It’s time to put your favorite soda to the test in this fun experiment with soda and Mentos! Does one brand produce higher-flying geysers? How does generic soda stack up against the big-name brands? If you’re doing a science fair project, your initial question might be: “What is the effect of the brand of soda on the height of the geyser?”

Use your data from the previous test to determine the standard number of Mentos candies to use for this test. The only variable you’ll change in this test is the brand of soda; everything else will remain the same (for example, the number of Mentos and the amount of soda). Again, make sure all of the soda is at the same temperature. That’s because temperature plays an important role in the reaction, too. The brand of soda is the only thing that changes (the variable).

Just think — your results could be the catalyst for the next Mentos Geyser Experiment craze!

 

The Temperature Test

What is the effect of temperature on the height of the geyser? Does warm Diet Coke and Mentos versus cold Diet Coke and Mentos make a difference? Does warm Diet Coke create a higher geyser explosion than does 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.

To enforce the fairness factor, you must stick with one brand of soda for the entire test. Let’s use Diet Coke in this example. You’ll want to purchase three bottles of Diet Coke and two 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 there overnight. Place the second bottle in a place where it will 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 a 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 (counting bricks or using an alternative scale against the wall). Let’s start with the bottle of cold Diet Coke. Open the bottle and dip the thermometer down into the soda. Record the temperature. Load seven Mentos mints into your paper roll or your Steve Spangler Science Geyser Tube and drop them into the soda. Immediately record the data for the cold soda test. Repeat the same procedure for the bottle of soda at room temperature and then again for the bottle of warm soda. It’s important to use the same number of Mentos for each test and to drop them into the soda bottles the exact same way.

No matter which brand of soda you tested, the warm bottle probably produced the highest-shooting geyser. 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 that at the bottling plant, the CO2 is pumped into the cans or bottles when the fluid is just above freezing — around 35 degrees Fahrenheit. This low temperature allows the maximum amount of CO2 to dissolve into the soda, keeping the carbonation levels as high as possible.

Take It Further

Take it Further

Simply dropping Mentos mints into a bottle of soda to make a geyser isn’t really science — it’s just a fun trick to do in your backyard. The real learning takes place when you start to change one variable at a time to see how it affects the performance of the geyser.

The Big Blast

After completing all of these tests, you’ve become somewhat of a Mentos Geyser Experiment expert who has the research to support the answer to this question: “How can you make the highest-shooting Mentos geyser?” Each test isolated an independent variable. Combining all of the information you observed into one launch is a great way to wrap up your science fair project! For example, based on your individual test results, you might have arrived at this recipe for the best Mentos Geyser:

  • Use a bottle of Diet Coke
  • Make sure the soda is at least 85 degrees Fahrenheit
  • Drop seven Mentos into the soda all at the same time

By using the scientific method and some critical thinking skills, you’ve successfully turned a great gee-whiz science trick into an exciting and explosive research-based science fair project!

Science Fair Connection

Science Fair Connection

You may be asking yourself, “Can I use the Mentos Geyser for my science fair project?” 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 a single variable is isolated. Then, observe, record and report the results.

To get the best results in a science experiment, you will need to standardize the test conditions as much as possible. The biggest challenge in the Mentos Geyser Experiment is finding a consistent way to drop the Mentos into the soda every time. This was the original reason I invented the Geyser Tube toy: to find a way to standardize the actual drop of the Mentos mint candies. If you’re not using the Geyser Tube, make sure to come up with your own method for dropping the Mentos mints into the soda exactly the same way each and every time.

Mentos and Coke Geyser Phenomenon History

As strange as it might sound, the Mentos Geyser Experiment never actually started out using Mentos chewy mints. This science demonstration was popular among chemistry teachers back in the 1980s. Instead of Mentos mints candy, however, they used a roll of Wintergreen LifeSavers and a pipe cleaner. Teachers threaded the roll of Wintergreen LifeSavers onto a pipe cleaner as an easy way to drop all of the LifeSavers into the soda at the same time. Within seconds of dropping the candies into the soda, a huge geyser would erupt from the bottle.

By the end of the 1990s, however, the manufacturer of Wintergreen LifeSavers increased the size of the mints (no one was ever certain why). This made the diameter of the candy too large to fit into the mouth of the soda bottle. Science teachers started experimenting (as they like to do) with other candies and mints that would have the same effect when dropped into a bottle of soda. As luck would have it, the solution to the problem was within arm’s reach of the Wintergreen LifeSavers in the candy aisle: Mentos chewy mint candies!

Because Mentos mints didn’t have holes in the middle like LifeSavers, getting them into the bottle was a little tricky. Everyone found their own method for quickly dropping the Mentos into the soda. Some people fashioned a tube out of paper; others used a piece of plastic tubing to load the Mentos. At the time, my solution was to load the Mentos candies into something called a “Baby Soda Bottle” — a test tube-like container that held an entire roll of Mentos perfectly. Oddly enough, this container was actually a “pre-form” or 2-liter soda bottle before it was blown up into a big bottle. That’s why it’s called a Baby Soda Bottle!

Troubleshooting Ensued

I must admit, however, that even with the Baby Soda Bottle method, the results were not very consistent. It proved challenging to get away from that bottle before it exploded. For that reason, I solicited help from our creative team at Steve Spangler Science to come up with a Geyser Tube — a better, more consistent way to drop the Mentos candies into the 2-liter bottle. Better yet, if we could trigger the drop of the Mentos from a distance, we wouldn’t get as wet.

Experimenting with Trigger Devices

The next few months were spent building trigger devices that ranged from plastic tubes with sliding doors and magnets that held metal stoppers in place to an elaborate battery-operated switch that was triggered by a motion detector. We even played with ways to use the Geyser Tube to trigger multiple soda geysers in a method similar to a Rube Goldberg machine. The bottom line was that we needed to find a way to standardize the drop of those Mentos mints.

As they say, the simplest design usually turns out to be the best and most elegant solution to the problem. The winning Geyser Tube design was a clear plastic tube with a special fitting that twisted onto any soda bottle. The trigger pin at the bottom of the tube prevented the Mentos from falling into the bottle until you pulled the string attached to the pin. The moment the pin was pulled, a slider ring resting above the pin fell into place and covered the holes where the trigger pin once was. The Mentos mints then dropped into the soda. But there was one added bonus: the restricted hole at the top of the plastic tube helped to build up more pressure in the bottle and launched the soda up to 30 feet into the air!

Fortunately, the maker of Mentos (Perfetti Van Melle) also liked our Geyser Tube design. We launched the Mentos Geyser Tube toy at the New York Toy Fair in February 2007.

A Television and Live Stage Phenomenon

The Mentos Geyser Experiment became one of my featured demonstrations — both on television and during my live stage presentations. While I had performed variations of the Mentos Geyser Experiment on television many times from 2001 to 2004, my performance of the demo in the backyard of Denver’s NBC affiliate KUSA-TV in September of 2005 proved to be the tipping point. The demo went from relative obscurity to an internet sensation!

My cohost for the KUSA-TV science segment was the lovely Kim Christiansen. During the commercial break, I told Kim what was going to happen and reminded her to pull her hand out of the way of the erupting geyser and to run backward. Unfortunately, Kim got so caught up in the fun that she forgot to do both — and got soaked in Diet Coke on live television! To add insult to injury, she did it two more times. Each time, she was covered in more soda until her once-pink dress was now more Coke-colored than pink!

KUSA-TV News posted that original video on their website along with my blog post titled, “News Anchor Gets Soaked!” Within a few weeks, links to the video and my blog entry numbered in the thousands. I also posted the video on a new online video-sharing site called YouTube (YouTube was only seven months old at that time). As they say, the rest is history. Within the next 12 months, over 800 Mentos Geyser Experiment-related videos were posted on YouTube, making the demo one of the most popular pop-culture science experiments in recent history.

The Million Dollar Question

We knew the Mentos Geyser Experiment was a popular experiment when a producer from ABC’s Who Wants to Be a Millionaire called for help when writing a question. Here’s the question we came up with:

In an experiment popularized online, what candy creates an explosive geyser when dropped into a 2-liter Diet Coke bottle?

  1. Skittles
  2. Mint Mentos
  3. Atomic Fireballs
  4. Lemon Heads

The question was asked on a special College Week episode of Who Wants to Be a Millionaire. The participant got it right for $8,000, saying: “I saw it on TV, and I bought Mentos and a 2-liter bottle of Diet Coke. So, I’m going to go with Mentos. That’s my final answer.”

The contestant ended up doing really well, going all the way to the $250,000 question; however, he walked away with $125,000.

Steve Spangler Science Online Experiment Library

Don’t miss our other super-fun and hands-on experiments in our huge online experiment library! From after-school activities and science classroom activities to STEM club experiments, our website is one of the most trusted resources for fun, age-appropriate experiments for kids of all ages.

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