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Students love Diet Coke and Mentos! Most have seen it on the internet and some have even placed Mentos in Diet Coke, but they can now experience the phenomena and learn the chemistry behind it!
Concepts include: Difference between chemical change and physical change, evidence for chemical changes, phases of matter, how to control chemical reactions with surface area, concentration, temperature and catalysts. Students collect data and create graphs to then analyze the data. There is a Common Core ELA component and they do research on exploding water in microwaves and relate that to Diet Coke and Mentos all in the 5e format.
The materials needed are: 2 rolls Mentos, one whole and one crushed, Two 2L Diet Coke bottles, Meter Stick, Two 3x5 cards, Tape, Camera, Mortar and pestle or something to crush Mentos and 2 beakers.
ENGAGE: I first play the Diet Coke and Mentos Mythbusters video and front load the question, “Do you think it’s a chemical change, physical change or both?”
EXPLORE-1: After the Mythbusters clip we discuss the question more and then read the 3 paragraphs under “Explore-1” and the students learn it is only a physical change and not a chemical change. However, increasing temperature, increasing surface area and increasing concentration can increase physical reactions. In this situation crushing it actually decreases the geyser because the craters or nucleation sites on the Mentos get destroyed when they are crushed so there are fewer craters for the carbon dioxide to form.
EXPLORE-2: The students then model their prediction, rather than do a traditional hypothesis. Developing and using models is one of the Science and Engineering Practices in NGSS. I tell them that this is their hypothesis in the form of a diagram/model. I tell them they need to draw the chemistry that is happening, molecules, bubbles, arrows and words and phrases need to be included as well. It should be clear as to what variable (whole or crushed Mentos) would create a bigger geyser in their model/diagram.
EXPLORE-3: This is where the students test their prediction. Each group of students need to bring in a phone to video the geyser, 2 rolls of Mentos and 2 two liter bottles of Diet Coke. I provide the mortars to crush the Mentos and beakers to measure the volume of remaining soda after the geyser. I have tape on the side of the building in 0.25m increments so they can measure the height of the geyser on their phones.
EXPLAIN: In this segment the students analyze their data and then revise their models/diagrams which is a very important aspect of developing and using models. The students also write an essay answering the questions and analyzing the data in the form of a paragraph.
EXTEND/ELABORATE: In this segment students watch the Mythbusters clip called “Superheating of Water” (https://www.youtube.com/watch?v=1_OXM4mr_i0)
Then they do some online research and answer 3 questions making sure they include States of matter and or phases of matter, boiling point, nucleation, superheating and homogeneous in their answers.
(1) Explain how exploding water in microwaves relates to nucleation?
(2) How is this related to our experiment with Mentos and Diet Coke?
(3) Explain how to use nucleation to avoid exploding water in microwaves.
Thank you so much!
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