Coke® & Mentos® - Nucleation Goes Nuclear!

Related Links

• Science Fair Project Guide

Project Summary

Difficulty	2  –  3
Time required	Very Short (a day or less)
Prerequisites	None
Material Availability	Readily available
Cost	Very Low (under $20)
Safety	Wear safety goggles so you won't get sprayed in the eye!

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Objective

In this experiment you will test if the number of dimples (nucleation sites) added to a Mentos® candy will change the height of exploding soda.

Introduction

The Diet Coke® and Mentos® eruption can be several meters high! (Wikipedia, date unknown)

The Diet Coke® and Mentos® experiment 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.

The first half of the story is something called a saturated solution, which is in this case a carbonated beverage or soda pop. All of the bubbles in a soda pop that make you burp come from carbon dioxide gas that is dissolved into the soda solution. While the soda is in the bottle, the gas is kept in solution by the pressurized conditions inside the bottle. But after you pour some soda into a glass, the gas bubbles stay trapped in the solution by the surface tension of the water. No wonder soda makes you burp— those gas bubbles are just sitting in there waiting to escape!

The second half of the story is something called a nucleation site. 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. Each tiny bump acts like a nucleation site, a place where this physical reaction can get a kick start. Each tiny nucleation site becomes a place where a bubble of carbon dioxide gas can form and escape the solution. Multiply that by all of the tiny bumps on a Mentos® and you have yourself a geyser!

In this experiment, you will see if adding extra, larger nucleation sites to the Mentos® candy will increase the height of the eruption. You will add extra dimples into the surface of the Mentos® candy, 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, Concepts and Questions to Start Background Research

To do this type of experiment you should know what the following terms mean. Have an adult help you search the Internet, or take you to your local library to find out more!

• Physical and chemical reactions
• Nucleation sites
• Carbon dioxide
• Surface tension
• Solution

• What makes the Diet Coke® suddenly form a geyser?
• How do nucleation sites provide a place for the carbon dioxide gas to escape the solution?
• Why is this a physical reaction and not a chemical reaction?

Bibliography

• Here is the Diet Coke® and Mentos® phenomenon described by the folks at Eepybird:
  EepyBird.com, 2006. "How Does It Work?," Eepybird.com [accessed June 6, 2007] http://eepybird.com/science1.html
• Here is a more technical description by Fred Senese at the Department of Chemistry at Frostburg State University in Maryland:
  Senese, F., 1999. "Why do Mentos mints foam when you drop them into soda pop?," General Chemistry Online, Frostburg State University, MD. [accessed June 6, 2007] http://antoine.frostburg.edu/chem/senese/101/consumer/faq/mentos.shtml
• This is what Wikipedia says about the Mentos® and Coke® eruption.:
  Wikipedia contributors, date unknown. "Mentos eruption," Wikipedia, The Free Encyclopedia, [accessed June 6, 2007] http://en.wikipedia.org/w/index.php?title=Mentos_eruption&oldid=138066475
• This is what Wikipedia specifically states on nucleation:
  Wikipedia contributors, date unknown. "Nucleation," Wikipedia, The Free Encyclopedia, [accessed June 6, 2007] http://en.wikipedia.org/w/index.php?title=Nucleation&oldid=136805690

Materials and Equipment

• 3 packages of Mentos® mint flavored candies
• 2 Index cards
• (3) 2 Liter bottles of Diet Coke®
• Sharp, pointy metal skewer or nail
• Video camera with tripod
• Blue painter's tape
• Tape measure
• Ladder
• Volunteer
• Eye protection (goggles or glasses)
• Outdoor space next to an exterior wall where tape can be applied (with permission)

Experimental Procedure

1. First, you will need to organize your Mentos® candies for the experiment. Each pack of Mentos® comes with 14 candies inside, so if you eat 2 candies you will have enough left for three trials with four candies each (12 total).
2. Each package of Mentos® will be given a different number of dimples. The first package will have no dimples added, so leave the first package alone.
3. The second package will have one small dimple added to each side. Using a sharp, metal skewer or nail, dig into the center of the Mentos® candy to make a small dimple. Flip the candy over and put one on the other side. Repeat with all of the Mentos® in the second package.
4. The third package will have five small dimples added to each side. Using a sharp, metal skewer or nail, dig into the center of the candy to make a small dimple. Then make four more dimples around the center dimple, making a five dot pattern. Flip the candy over and make five more dimples on the other side. Repeat with all of the Mentos® in the third package.
5. 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.

   Here is how one science fair student from Marin County, CA set up his Diet Coke® and Mentos® experiment.

6. Now, prepare your test site. 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. You will need a ladder and an adult's help to mark off the taller measurements.
7. Set up the video camera with a tripod, and make sure that the soda bottle and marked measurements are in view. Show your volunteer how to start and stop your video camera. Your experimental set up should look something like this:
8. Remove the cap from the soda bottle and place the flat index card on top, covering up the hole.
9. Starting with the first package of Mentos® (the one with no dimples) add four Mentos® to your cartridge and put on your safety goggles.
10. Have your volunteer start the video camera and before each trial, speak into the camera and say, "This is trial number (1, 2, 3...) using Mentos® with (0, 1, or 5) dimples." This will help when you go back to analyze your results.
11. Place your full cartridge on top of the flat index card. 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. When the bottle stops spouting, stop recording.
12. Repeat step 11 two more times, for a total of three trials using four Mentos® candies each time.
13. Repeat steps 9–12 with the other two packages of Mentos®. Go in order so that you can keep track on your video tape.
14. Now you are ready to watch your tape and analyze your data. As you watch the tape for each trial, use slow motion and pause the recording when the spout is at its maximum height. Then using the tape marks in the background do your best to estimate the height of the spout. Do this for each trial and keep your data in a data table:

    Number of Dimples	No Dimples	One Dimple	Five Dimples
    Trial 1 Height (m)
    Trial 2 Height (m)
    Trial 3 Height (m)
    Total Height (m)
    Average Height (m)

15. Make a graph of the average height (in feet) of the spout versus the number of dimples. What does your data mean? Do you think that providing the extra nucleation sites made a difference?

Variations

• You can expand this experiment in many different ways to make it unique:
  • Test different kinds of carbonated beverages.
  • Try different kinds of candies with different shapes and textures.
  • Try using other things to start the reaction, like rock salt, pennies, or dice.
  • Try drilling different sized spout holes in the cap to see if that will make a difference.
• Can you think of another more accurate way of measuring the reaction using volume? This method uses more bottles of soda, but is more accurate. You will need a balance and a graduated cylinder.

• For more science project ideas in this area of science, see Materials Science Project Ideas

Credits

Sara Agee, Ph.D., Science Buddies