Coke® & Mentos® - Exploring Explosive Chemistry!
AbstractYou have probably seen it on You Tube™ — the exploding Coke® and Mentos® experiment. But what is it that makes the reaction happen, and what factors cause a larger or smaller eruption? In this science project, you will see if using crushed Mentos candies, instead of whole Mentos candies, will affect the reaction.
Sara Agee, Ph.D., Science Buddies
Teisha Rowland, Ph.D., Science Buddies
Determine if using crushed Mentos candies will change the height of exploding soda compared to using whole Mentos candies.
The Diet Coke and Mentos experiment (shown in action in Figure 1 below) is all over the Internet, but how does it work? You might think that there is some ingredient in a Mentos candy that is causing a chemical reaction with the soda, like the way baking soda reacts with vinegar. But this is not a chemical reaction at all! Instead it is a physical reaction. That means that all of the pieces of the reaction are there, but that they are simply re-arranged.
Figure 1. The Diet Coke and Mentos eruption can be several meters high! (Wikipedia, date unknown)
A carbonated beverage, like a soda pop, is packed full of carbon dioxide gas that is dissolved into the soda solution. All of the bubbles in a soda pop that make you burp come from the dissolved carbon dioxide gas, which forms bonds with water. While the soda is in the bottle, the gas is kept in solution by the pressurized conditions inside the bottle. When you pour some soda into a glass, the gas stays trapped in the solution by the surface tension of the water. But those gas bubbles want to escape, making it no wonder that soda makes you burp!
To create bubbles, the carbon dioxide needs to interact with itself, which means that its bonds with water in the soda must be broken. A Mentos candy can help with this. Looking at a piece of Mentos candy, you may think it is very smooth. But if you were to look under a microscope, you would see tiny bumps coating the entire surface of the candy. This rough surface allows the bonds between the carbon dioxide gas and the water to more easily break, helping create carbon dioxide bubbles that cause the classic Mentos and Diet Coke eruption. This means that each tiny bump acts like a place where the physical reaction can get a kick start, where a bubble of carbon dioxide gas can form and escape the solution. As the Mentos candy sinks in the bottle of soda, the candy causes the production of more and more carbon dioxide bubbles. The rising bubbles react with carbon dioxide that is still dissolved in the soda to cause more carbon dioxide to be freed and create even more bubbles. With all of the tiny bumps on a Mentos, it is easy to see how you have yourself a geyser!
One factor that may affect the size of the Mentos and Diet Coke eruption is how quickly the Mentos candies sink in the soda. Because a Mentos candy is relatively dense, meaning that its particles are very tightly compacted together, it sinks relatively quickly in the soda. If a Mentos candy were crushed and broken into little pieces, the candy would be less compact, and consequently less dense, because there is now more space and air between the little pieces. The crushed Mentos candy should sink slower than a whole Mentos candy. In this materials science project, you will see if using crushed Mentos candies instead of whole Mentos candies, which should sink faster in the soda, will change the height of the eruption. You will crush Mentos candies and then use them to make Diet Coke geysers. You can measure the height of the geyser with a wall, a helper, and a video camera. What will be your highest height?
Terms and Concepts
- Chemical reactions
- Physical reactions
- Carbon dioxide
- Chemical bonds
- What makes the Diet Coke® suddenly form a geyser?
- How do the bumps on a Mentos® candy provide a place for the carbon dioxide gas to escape the solution?
- Why is this a physical reaction and not a chemical reaction?
- How might the speed at which the Mentos® candy sinks in the soda affect how large the geyser is?
These resources are good places to start gathering information about the Mentos® and Diet Coke® reaction:
- # Link Name="MatlSci_p023.1" Value="HtmlAnchor" HtmlText="EepyBird.com." #] (n.d.). The Science of Coke and Mentos.. Retrieved June 26, 2012.
- Muir, H. (2008, June 12). Science of Mentos-Diet Coke explosions explained. New Scientist.. Retrieved June 26, 2012.
- Senese, F. (2010, February 15). Why do Mentos mints foam when you drop them into soda pop? General Chemistry Online!. Retrieved June 26, 2012.
For help creating graphs, try this website:
- National Center for Education Statistics, (n.d.). Create a Graph. Retrieved June 25, 2020.
Materials and Equipment
- Mentos® mint flavored candies (24 candies)
- Wax paper
- Cutting board
- Index cards (at least 2)
- 2 L bottles of Diet Coke® (6)
- Blue painter's tape; This can be purchased at most hardware stores or online at Amazon.com.
- Metric tape measure or meter stick
- Video camera
- Optional: Tripod for the video camera
- Eye protection, such as goggles or glasses
- Permanent marker
- Graduated cylinder or measuring cup
- Outdoor space next to an exterior wall where tape can be applied with permission
- Lab notebook
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First, you will need to prepare your crushed Mentos candies. You may want an adult to help you crush the Mentos candies.
- Place a piece of wax paper on top of the cutting board.
- On the wax paper, carefully use the knife to crush and cut four Mentos candies into many small pieces, as shown in Figure 2 below. Cut each candy in to at least eight pieces. What does the inside of the Mentos candies look like?
- When all four candies are cut into pieces, carefully set the piece of wax paper, with the candy pieces still on it, aside somewhere safe.
Repeat steps 1a to 1c two more times so that you have three groups of candy pieces.
- You will be testing the crushed candies in three separate trials. It is important to repeat your experiment so that you are sure that your results are repeatable and reproducible.
Figure 2. On a piece of wax paper, carefully crush and cut four Mentos candies into many small pieces, as shown here. Prepare three groups of crushed and cut Mentos like this one.
Next, you need to make your Mentos cartridge to hold the Mentos for you before you drop them into the soda bottle.
- Take one of the index cards and roll it into a tube, slightly larger than the diameter of a Mentos candy. Tape the tube together on the side, and now you have a cartridge for holding your stacks of Mentos.
- You will use the other index card to place beneath the tube of Mentos, to keep the Mentos from dropping into the soda bottle until you are ready.
Figure 3. Here is how one science fair student from Marin County, CA set up his Diet Coke and Mentos experiment.
Now, prepare your test site so you will be able to measure how high the geysers go.
- At the base of an exterior wall with no windows, set one bottle of Diet Coke.
- On the exterior wall, use a tape measure and the blue painter's tape to mark off the height from the top of the soda bottle in meters (m), as shown in Figure 3. You will need a ladder and an adult's help to mark off the taller measurements.
Set up the video camera with a tripod, if available, and make sure that the soda bottle and marked measurements are in view.
- To prevent soda from possibly splashing the camera or volunteer, do not place the video camera too close to the testing spot.
- Show your volunteer how to start and stop your video camera.
You are now ready to film some Mentos and Diet Coke eruptions! First test the whole Mentos candies and then try the crushed Mentos candy pieces. You should wear clothes that you would not mind having a little Diet Coke splashed on to!
- Place an unopened Diet Coke bottle at the outside area that you marked off, at least 2 m from the building and away from anything hanging above the area, such as eaves, overhangs, or wires. Make sure that the bottle is level and stably standing straight up. Why do you think all of this is important?
- Carefully remove the cap from the soda bottle and place the flat index card on top, covering up the hole.
- Add four whole Mentos to your cartridge and put on your safety goggles.
Have your volunteer start the video camera and speak into the camera and say, "This is trial number 1 using whole Mentos."
- This will help when you go back to analyze your results. In subsequent trials, have your volunteer say the new trial number (such as 2, 3, 4) and whether it is using whole or crushed Mentos.
Place your full cartridge on top of the flat index card. Line up where the opening of the bottle is with the opening of your cartridge. When you are ready, quickly remove the flat index card by pulling it, releasing the Mentos into the bottle. Step back without tipping the bottle over or disturbing the reaction.
- Tip: The reaction will start very quickly, so be ready to take away the empty cartridge and step away from the bottle as soon as the candies fall into the soda!
- When the bottle stops spouting, stop recording.
- Remove the used Diet Coke bottle and set it aside. Do not pour out the remaining soda yet! Use the permanent marker to label the bottle with the trial number, and whether it was used with whole or crushed Mentos candies.
- Repeat steps 5a to 5g two more times, for a total of three trials using four whole Mentos candies each time.
Repeat steps 5a to 5g three more times, but this time use the crushed Mentos candies you prepared in step 1. Use four crushed Mentos candies each time.
- In step 5c, use the funnel to help you load the crushed Mentos candy pieces into your cartridge.
Now you are ready to watch your videos and analyze your data.
In your lab notebook, make a data table similar to Table 1 below.
Trial Reaction Time (sec) Geyser Height (m) Soda Volume Remaining (mL) #1: Whole Mentos #2: Whole Mentos #3: Whole Mentos Average Whole Mentos #4: Crushed Mentos #5: Crushed Mentos #6: Crushed Mentos Average Crushed MentosTable 1. In your lab notebook, make a data table like this one to record your results in.
To determine the reaction time of each geyser, watch the videos for each trial and note the time for when the geyser starts and when it stops.
- In the data table in your lab notebook, write down the total amount of seconds (sec) that the geyser lasted for each trial.
To determine the height of each geyser, watch the videos for each trial using slow motion and pause the recording when the spout is at its maximum height.
- Use the tape marks in the background to do your best to estimate the height (in meters) of the spout. Write this in your data table.
To find out the volume of Diet Coke remaining in the bottle after the eruption, pour the remaining soda into a graduated cylinder (and measure in milliliters [mL]) or into measuring cups (and measure in cups).
- For each trial, calculate the total amount of remaining soda in the bottle and write this in your data table.
- Calculate the average reaction time, geyser height, and soda volume remaining for the trials using whole Mentos and the trials using crushed Mentos. Write these averages in your data table.
- In your lab notebook, make a data table similar to Table 1 below.
Make three bar graphs of whole Mentos versus crushed Mentos: One graph of the average reaction time, one of the average geyser height, and one of the soda volume remaining.
- You can make the graph by hand or use a website like Create a Graph to make a graph on the computer and print it.
- For each graph put whole Mentos and crushed Mentos on the x-axis (the horizontal axis) and average reaction time, average geyser height, or soda volume remaining on the y-axis (the vertical axis).
- What does your data mean? Do you think that using crushed Mentos, which should have sunk slower in the soda, made a difference in the reaction? Were your results what you expected them to be, or were they different? Why? How do you think the reaction time, geyser height, and soda volume remaining might correlate with each other?
Ask an Expert
- In this science project, the focus was on comparing crushed Mentos to whole Mentos candies, but you can do several similar projects that test different aspects of this reaction. Some other
project ideas are:
- Test different kinds of carbonated beverages, such as regular Coke versus Diet Coke or other carbonated beverages.
- Try different kinds of candies with different shapes and textures.
- Try using other things instead of Mentos candies to start the reaction, like rock salt, sand, pennies, or dice.
- Try using Diet Coke that is warm, cold, or at room temperature.
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