Working With the And Coke Experiment Worksheet
The Diet Coke and Mentos reaction is one of the most common middle-school and high-school chemistry demonstrations, and most teachers have their own version of a lab worksheet to go with it. I have graded hundreds of these over the years, so I know what works and what turns into a mess on the second day of the unit. A standard worksheet for this lab typically has three parts. The first section asks students to record variables like bottle volume, mint quantity, and temperature. The second section covers the procedure, and the third asks for calculations around reaction rate, height of the geyser, or pressure changes inside the bottle. Some versions include a prediction column where students write hypotheses before they actually do the experiment. I use a slightly modified version. The printed worksheets from publisher websites tend to skip the part about surface area of the mints, which is actually the biggest factor in the reaction. If your students are just dropping whole mints into the bottle, you will get inconsistent data every single time. I tell them to shred the mints into two separate batches — one fine, one coarse — and measure the geyser height with each. The difference is usually obvious even without precision instruments.
Here is how I structure the actual lab period when using the worksheet. First, the students fill out the variable table before touching any materials. Then they run the trial with whole mints and record the peak height. After that, they test crushed mints and uncrushed mints at different soda temperatures. By the end, they are filling in a comparison table on the back of the sheet, and they can see the relationship between surface area and reaction intensity directly in their own numbers. It takes about twenty minutes for the full set of trials, and cleanup is roughly five minutes if you have wet paper towels ready at each station. One edge case that always trips people up is the brand of Coke. Diet Coke reacts dramatically more than regular Coke because the artificial sweetener changes the surface tension differently than sugar does. I have seen entire classes get confused when their data looked nothing like the textbook example, and the problem was that their school stocked the regular version instead of Diet. The worksheet does not always call this out, so I add a note on the board before they start: make sure your bottle says Diet, and write down which brand you are using in the materials log. There are some real limitations to this whole setup that the worksheet side never mentions. The reaction itself is too fast to measure with basic stopwatches. Students who try to time from drop to peak are usually off by half a second or more, and that introduces a lot of noise into the rate calculations. A phone camera recording at 240 frames per second solves this, and most modern smartphones can do it without any special equipment. Just prop the phone against a water bottle on a shelf and let it roll.
Another thing nobody warns you about is the bottle opening. Standard Coke bottles have a narrow mouth, which means the geyser often gets partially blocked right at the start. This creates a pressure buildup that can cause the bottle to bulge or even crack if the student keeps adding mints too quickly. I recommend using a two-liter bottle and only ever dropping three or four mints at once. Anything more and you are working with forces the plastic was not designed to handle repeatedly. Once, a student tried about ten mints and the cap blew off with enough force to shatter a nearby beaker. The worksheet assumes the reaction is predictable. It is not, not past a certain threshold of mint mass. If you are looking for a downloadable version, most state education department websites and university extension programs host free copies. The one I rely on comes from the Tennessee Science Standards alignment page, though they update the PDF occasionally and the URL shifts. Search for "Diet Coke Mentos lab worksheet Tennessee DOE" and the current version should appear. It has a cleaner data table than the commercial publishers, and it includes a section on nucleation sites that regular worksheets often leave out. The science behind the experiment is straightforward enough that the worksheet does not need to overcomplicate it. Carbon dioxide comes out of solution when the rough surface of the mint provides nucleation points. The foam rises because gas bubbles get trapped in the liquid, and the density difference pushes the column upward. That is the core mechanism. Surface area, temperature, and carbonation level are the variables that shift the outcome. Pressure inside the bottle rises during the reaction, which is why wider openings produce taller but shorter-lived geysers while narrower openings create pressure buildup.
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For teachers who want to push beyond the basic worksheet, there is a second round of questions that works well. Have students predict what happens with warm versus cold Diet Coke. Cold soda holds more dissolved CO2, so the reaction is actually more vigorous at lower temperatures, which is counter-intuitive for most students. Then ask them to test different mint flavors. Sugar-free mint varieties tend to produce slightly different results because the coating on the candy varies, and the gelatin content in some brands affects how quickly the surface breaks down. This is where the worksheet becomes a starting point rather than the endpoint. I have found that the best results come from treating the worksheet as a framework, not a script. Students learn more when they fill in the blanks with their own observations instead of matching numbers to an answer key. The reaction is visually engaging, but the data quality depends entirely on how carefully they control the variables. Add a reminder about that on day one and you will save yourself a lot of grading headaches later. One more practical note about the worksheet format. Many versions print both sides on a single page, which makes the data tables cramped and hard to read under fluorescent classroom lighting. I always reprint the data collection section on a separate half-sheet and staple it to the front. Students write in pencil, and they can erase and redo trials without cluttering the main worksheet. It is a small change, but it cuts the number of blank pages I have to collect and sort by nearly half.
The experiment itself is safe when done with proper supervision. The main hazards are slipped soda, sticky floors, and the occasional flying cap. Wear goggles, stand back after the first mint goes in, and keep a trash bag nearby for the wet paper towels. Beyond that, it is a standard classroom lab with no special permissions required. If you are a student using this worksheet on your own, the most useful part is the comparison table. Write down every variable you can measure — temperature, mint count, crush size, bottle type — and treat it like real data instead of a homework filler. The patterns are there if you actually look at them.
