Diet Coke and Mentos Science Experiment

For this experiment you will only need three things:
1. 3 Liter bottle of diet coke
2. Roll of Mint flavored Mentos
3. Wear old clothes and a pair of safety glasses. The explosion can get pretty large!
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You may place as many Mentos inside the coke as you would like. The more Mentos that are added to the coke, the larger the reaction will be. To achieve the best reaction, put the entire roll in the coke. Start by unscrewing the cap to the coke. Unwrap the outer layer of paper and leave the remaining silver paper in place,(allowing the mentos to stay in the tubed shape,) making it easier to place the mentos into the coke bottle. As soon as you have placed the mentos into the bottle STEP BACK! The reaction is immediate. You should see a stream of coke shooting out of the bottle much like the pictures from above.

The Science Behind the Experiment

There are two types of reactions, chemical and physical reactions. A chemical reaction changes the forms of the elements in the experiment like combining baking soda and vinegar. A physical reaction does not change the elements that are involved. Think of stirring water and oil together. They do not change when you mix them together right? The water and oil is a n example of a physical reactions. ´╗┐The coke and mentos reaction is also physical reaction. The coke contains dissolved Carbon Dioxide (that's what makes the coke bubbly) . In order for the substance inside the coke to expand, the molecules must be pushed away from one another. The coating on the candy has a substance that breaks up the surface tension of the coke when they are placed inside, and they help to produce bubbles. The reason Diet Coke Works better than Regular Coke is because the artificial sweeteners work better than sugar to help break up the surface tension in the coke.

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(This Picture is nucleation of carbon dioxide around a finger)

The surface of mentos is covered with many tiny craters. These craters act as nucleation sites and help to form the bubbles. Nucleation is extremely localized budding of a distinct thermodynamic phase. Nucleation is when something changes form in a very exact site. When the mentos sink to the bottom, they automatically have a physical reaction with the coke. The low surface tension of the coke, and the nucleation sites found on the candy, create a large amount of bubbles in a short amount of time. The space in the bottle is very small for the amount of force produced by this reaction. So, the coke exits the bottle in an eruption. This is the Coke Geyser!

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To help further explain the science behind this experiment watch this video of MYTHBUSTERS.





Citations:
http://aftermathmagazine.blogspot.com/2009/01/mentos-and-diet-coke-truth-revealed.html
http://www.youtube.com/watch?v=LjbJELjLgZg
http://www.newscientist.com/article/dn14114-science-of-mentosdiet-coke-explosions-explained.html