Kids love to see chemical reactions, and experiments with Mentos and Diet Coke can bring some excitement to science class without introducing dangerous chemicals or breaking the bank. Mentos and Diet Coke together produce an explosive reaction that excites students and can inspire them to ask questions. Combining the experiment with an explanation of the science involved means that fun and learning can coexist as students learn a little about the world on a molecular level.
The Basic Experiment
Choose an area where you won't have to do much cleaning up, such as outside in the schoolyard on a sunny day. Open up a bottle of Diet Coke and roll up the Mentos candies loosely in a piece of paper. You want to roll them tight enough so that you can hold your paper tube of candy over the bottle, but loose enough so that releasing your grip will drop the Mentos straight down into the bottle of Diet Coke. Once you've let the candies plop into the soda, get out of the way quickly and watch the fireworks.
Run Comparison Trials
Challenge your students to find out if other combinations of liquid and solid substances have the same reaction. Record the trials so you can visually compare the height of different liquid streams later in the classroom. One group of students tried the reaction with both fruit Mentos and mint Mentos to see if the flavor of candy used made a difference. You can also try different combinations of other mints, dish soap, tonic water, soda water and soft drinks.
The Reaction Explained
The growth of carbon dioxide bubbles in Diet Coke explains the spectacular reaction. Polarized water molecules are attracted to each other, creating surface tension on top of the liquid. Anything dropped into the liquid disrupts the surface tension, becoming a growth site to which carbon dioxide bubbles attach themselves. Candies with dimpled surfaces, like Mentos, provide many nooks and crannies for bubbles to grow, resulting in a soda explosion. Since low surface tension helps bubbles gather, other chemical properties of Mentos and Diet Coke help account for the extreme reaction. Although both Coke and diet Coke create fountains of soda spray, the reaction with Diet Coke is more intense because the artificial sweetener it contains reduces the starting surface tension of the fluid. Mentos also contain gum arabic, a chemical that pushes water molecules apart and lowers surface tension.
Other Variations
Use the Mentos and Diet Coke experiment to create exploding volcanoes. Have students create paper mache volcanoes surrounding their Coke bottles. Let the creations dry overnight before painting them to look like the real thing. Wait for a sunny day, then take students outside to put on a show. Use cameras to photograph soda streams as they shoot up into the air. Students can experiment with different shutter speeds to create interesting effects. If you want to get technical, have kids edit their best shots to create artistic digital masterpieces.
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