Marvelous Mentos^TM

Introduction:  It's no surprise that Mentos are mostly sugar. What is surprising are some of the other ingredients found in Mentos including cornstarch, gum arabic. dextrin, gelatin, and even hydrogenated coconut oil.  Each of these combines to help provide Mentos with their own unique color, texture, and taste. While these tasty pellets are quite popular as a special treat, they can also be used to erupt the excitement of your students and engage them in thinking about science.   In this activity, your students will combine three Mentos pieces with a  Diet Coke, observe the unusual results, and develop an explanation that could possibly explain this amazing behavior.  You can watch the MPEG video below to see how much fun it will be with your kids.

The Mentos Movie

National Science Standard: Unifying Concept

Nature is constantly changing but there are many repeating patterns.

Georgia Performance Standards:

Students will exhibit curiosity, honesty, openness and skepticism S(K-5)CS1

Describe materials, what they are made of, and how they change. SKP1, S2P1,S5P2

Students will investigate the difference between physical and chemical changes S5P2

Materials: 

Roll of Mentos Candy         2 liter Bottle of Unopened Diet Coke      Extra 2 Liter Bottle Top

Drill                                        1/4 inch Drill Bit                                        Paper Clip

Safety goggles                      Towels for Clean-up

Teacher Led Exploration: 

This demonstration should be done outside or in a room with tiles and a high ceiling.

1. As students walk into class, ask them if anyone has ever eaten a Mentos. Then, ask them if they have ever drank a Coke .  Finally, ask them if they haven ever eaten a Mentos and drank a Coke at the same time. 

2. Next, ask students to predict what they think will happen when Mentos and Coke are combined together. Have students discuss their ideas in small groups and then have them write what they consider to me their most plausible prediction on the board. Briefly discuss each prediction. 

3. Bring the students outside and show them the three Mentos that you have rigged onto the paper clip.  Insert the extended portion of the clip up through the hole in the extra bottle cap and then remove the original cap from unopened bottle of Coke.  Explain to the students that you are going to carefully replace it with rigged cap which is holding the Mentos.  Be careful to hold onto the clip and Mentos while you are screwing the cap tight. Now carefully drop the Mentos (and clip) into the Coke and move quickly to the side. Observe carefully what happens.  Pretty amazing huh?   If time permits try it again with any other carbonated drink.  At Science Camp we did this demonstration with 50 kids and 50 bottles at the same time. It was a blast. 

4.   Bring your students back to class and ask them to discuss their predictions and observations. Have them develop a brief explanation that could be used to explain the unusual behavior of the Mentos and Coke. 

 Essential Questions:

1.  Based on your observations, what explanation can you develop to explain the behavior that you observed?

2. Would you classify this type of change as a chemical or physical change? Explain your reasoning.

3. What problems would you anticipate for people who drink Coke and eat Mentos at the same time?

4. The attraction of water molecule to each other is very strong, can you think of other examples that show how    strongly water molecules stick together?

Explanation:

In small groups or as a class, have students discuss their ideas regarding Mighty Mentos. For younger students, you may want to simply focus on the idea that substances can react with one another and change in the process. In this case, a surprising and great visual example of a chemical reaction (change).      

Concept Discussion:

When Coke and other beverages are produced, they are bottled with CO₂ gas that is pushed into the bottle at a pressure about 3 times that of normal air. This heavy pressure helps to thousands of the tiny CO₂  bubbles to dissolve in the Coke but the high pressure also keeps them very small.  But  when the bottle is opened and the pressure is released, these bubbles get a little larger and, as they escape to the surface, they provide the characteristic fizz or carbonation that most people find very appealing.   As it turns out though, these bubbles would get much bigger, much quicker if not for the fact that the water molecules in Coke (which is mostly water) attract strongly to one another. The attractive forces between water molecules forms a tight web around each bubble and this makes it difficult for the bubble to expand.   This attractive force, which is sometimes called "surface tension", is so strong that certain bugs (Waterstriders) can even walk on the surface of water without sinking.     

When Mentos are added to the Coke, the Mentos begin to dissolve and  the gelatin and gum arabic found in Mentos instantly act to break up the attractive forces between the water molecules.  It is now easier for the bubbles to grow and thousands of tiny bubbles can instantly expand to hundreds of times their original size.  Meanwhile, the rough surface of the Mentos provides many little nooks and cracks that help new bubbles to form. The combination of these two processes causes the carbonated gas to erupt from the bottle like a superheated geyser in Yellowstone Park. It is truly an amazing site.    

Teacher Notes:  

To prepare the bottle cap, place the cap on an empty bottle and then carefully drill a 1/4 inch hole through the cap as you hold the bottle.  Keep the cap so that you can use it over and over.  See pictures on page 1. 

To prepare the paperclip straighten it out so that only the inner loop remains. Poke holes through the center of the Mentos with the long  end of the paper clip (or a nail) and pull them down and attach them to the bottom loop. Then insert the long end through the bottom of the bottle cap and pull the Mentos up to the top of the cap. 

 Be careful not to drop the Mentos into the bottle before you have twisted the cap on tightly. You may choose to let a student do this and actually sit next to the bottle and hold on to it.  He/she will get soaked by the Coke but the class will have a great laugh. 

Safety Concerns:

While this demonstration is messy, it isn't very dangerous. You should have safety goggles on if possible when you drop the Mentos into the Coke.  

Evaluation and Closure:

      Student writing or journal entries should be evaluated to check for student understanding.