Summary

In this lab, students will design their own experiment in which they manipulate a variable that relates to Mentos and soda. Students will generate a testable question, design an experiment, collect and analyze the data and present their findings.

Grade Level

Middle and High School

NGSS Alignment

This lab will help prepare your students to meet the performance expectations in the following standards:

• MS-PS1-2: Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.
• MS-ETS1-1: Define the criteria and constraints of a design problem with sufficient precision to ensure a successful solution, taking into account relevant scientific principles and potential impacts on people and the natural environment that may limit possible solutions.
• Scientific and Engineering Practices:
  • Asking Questions and Defining Problems
  • Analyzing and Interpreting Data
  • Planning and Carrying Out Investigations

Objectives

By the end of this lab, students should be able to:

• Identify independent and dependent variables.
• Design a controlled experiment, and collect necessary data.
• Explain the difference behind a table and a graph.
• Make a relevant claim based on laboratory data.

Chemistry Topics

This lab supports students’ understanding of:

• Experimental Design
• Scientific Method
• Independent and Dependent Variables
• Graphing
• Observations
• Lab Safety

Time

Teacher Preparation: minimal
Lesson:  225 minutes (five 45 minute class periods)

Materials

Demonstration:

• One 2-L of regular (non-diet) cola
• 2 Mentos

Student Lab:

• Varieties of 2 Liters of soda
  • Quantities, brands, etc. of soda will depend on the experiments that your students design
• Varieties of Mentos
  • Quantities, brands, etc. of Mentos will depend on the experiments that your students design
• Computers
  • Data analysis using Google Sheets
  • Student Presentations
• Geyser tubes (optional, but highly recommended)

Safety

• Always wear safety goggles when handling chemicals in the lab. Use caution during launching, as the soda may react quickly resulting in spray into students eyes.
• Students should wash their hands thoroughly.
• When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
• Student testing should be conducted outdoors.

Teacher Notes

• It is best to start this project before a weekend so that students will have an opportunity to purchase their supplies.
• Below is a timeline of how I organize 5 class periods, each 45 minutes, to complete this lab experience. This outline can be modified if you do not have as much class time available, or if you have block scheduling.

Day 1:

• I engage students in this lesson by first demonstrating the launch of a Mentos and soda fountain. I intentionally do a mediocre job (using a 2-liter of regular, non-diet cola and two Mentos), but I hype it up like it’s going to be awesome. Based on the disappointing results, I then encourage students to change a variable about my experiment that will make the explosion and height of the fountain better. Be sure to do this demonstration outside.
• After this demonstration we return to the classroom and go through the presentation “Designing an Experiment”. This can be used either to refresh their memory about independent and dependent variables or to teach them the concepts.
• When thinking about potential variables for this experiment, below is a list of ideas:
  • Type of soda (diet, non-diet, dark-colored soda, clear-colored soda, etc.)
  • Brand of soda (RC, Coca-Cola, Store brand, Pepsi, etc.)
  • Type Mentos (fruit, regular, sugar free, cinnamon)
  • Brand of Mentos (name brand, store brand, other candy)
  • Size of bottle (2-L, 1-L, 16oz, etc.)
  • Fullness of bottle (a 2-L bottle full, half full, ¼ full, etc.)
  • Number of Mentos
  • Temperature of soda (fridge, room temp, hot water bath, etc.)
  • Size of Mentos (cut in half, whole, small parts)
  • Freshness of the soda (opened 24hrs before, 1 hour before, right before, etc.)
• Students form lab groups and begin completing the “Experiment Design Template”.
• Students must have their design approved before being able to complete their experiment.
• Depending on the level of your students, and the class time available, this may take them into the next class period to finish.
• I require that students bring their own supplies for their experiment. Often 2-L  sodas are available for $1 and Mentos are also $1 for a roll. These can be found at grocery stores, Walmart, discount/dollar stores, etc. Each group will need approximately $6 worth of supplies. However, I have purchased supplies with class funds for students if they cannot afford them or express a need for assistance.
• Using a geyser tube is not required, and the fountain will work without it, however using one tends to make for less mess and less soda overflow.

Day 2:

• Conference with student groups about their “Experiment Design Template”, if necessary.
  • The most common problem with their experiment design is typically the “Procedure” section, because they do not think through every step of directions that is needed. Often things that are missing include quantifies, such as a specific number of Mentos.
  • I find that it can be helpful to quickly pretend to conduct their experiment using their directions so they can see that there are missing steps.
  • Also, students will often create their table incorrectly which will make it difficult to graph their lab data later.
• Students may have supplies purchased and may begin testing if they have been approved.
• On Day 2, I often play a review game, like Kahoot!, or similar review activity focused on experimental design concepts, such as independent and dependent variables.

Day 3:

• All student groups should be ready to complete their experiments today, if they have not started already.
  • To measure height as the dependent variable, I typically have students conduct experiments by a brick wall so that you can measure and count the number of bricks that the fountain reached.
  • If it goes above the wall students should estimate the additional height.
  • Recording the experiment on video can be helpful to collect more accurate data.
• After completing their experiments they can begin creating graphs of their data and their presentations.

Day 4:

• I go through the presentation “Graphing Workshop”.
• I also review the expectations and instructions for the student presentations and discuss how their presentation will be graded. Refer to the “Presentation” handout for this information.
• Students are given the remainder of class to create their graphs and presentations that will be given the next day.

Day 5:

• Each student group will complete a short presentation about their experiment.
• After all of the presentations are complete, students will each complete the “Claim, Evidence, Reasoning” handout, and are tasked with using data from the presentations to answer the question, what combination of variables will create the highest Mentos and soda fountain?
• The purpose of this is for students to review and consider all the different experimental variables that were tested, and determine the very best combination for the highest possible fountain.

Extensions:

• Students can read and discuss the article, “Science of Mentos—Diet Coke Explosions Explained”, by NewScientist, to learn about what causes the Mentos and soda fountain to occur.  
• You could also look at limiting and excess reactants with this experiment, especially with the number of Mentos as the amount of CO₂ begins to limit the height of the fountain after 5 Mentos.
• On the final day, I typically show students what should be the ultimate combination to generate the highest Mentos and Soda fountain. You can do this based on class responses to the Claim, Evidence, Reasoning assignment, or use the combination of warm diet cola with 7 Mentos.
• Students could discuss whether this is a physical or chemical change and how they know.