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Soda geyser

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"Geyser" produced by immersing Mentos into Diet Coke

A Mentos eruption (also known as a Mentos-and-Coke geyser) has become a backyard science experiment fad. It has also become an internet phenomenon, with videos of Mentos eruptions being posted on sites like YouTube and Google Video.

The experiment involves dropping several Mentos candies into a bottle of cola, resulting in an eruption. This reaction occurs because of the rapidly expanding carbon dioxide inside once the Mentos are introduced to the carbonation.

The science behind it

While there are various theories being debated as to the exact scientific explanation of the phenomenon, many scientists claim that it is a physical reaction and not a chemical one[1]. Water molecules strongly attract each other, linking together to form a tight mesh around each bubble of carbon dioxide gas in the soda. To form a new bubble, water molecules must push away from one another. It takes extra energy to break this surface tension. So, in other words, water resists the expansion of bubbles in the soda.

When Mentos is dropped into soda, the gelatin and gum arabic of the candy dissolves and breaks the surface tension. This disturbs the water mesh, so that it takes less work to expand and form new bubbles. Each Mentos candy has thousands of tiny pits all over the surface. These tiny pits function as nucleation sites, perfect places for carbon dioxide bubbles to form. As soon as the Mentos enters the soda, bubbles form all over the surface of the candy. The Mentos quickly sinks to the bottom, releasing carbon dioxide as it comes into contact with carbonated liquid along the way. The sudden increase in pressure pushes all of the liquid up and out of the bottle.

The reaction was the subject of an August 9, 2006 episode of MythBusters, a television program on the Discovery Channel. They concluded that the caffeine, potassium benzoate, aspartame, & CO2 gas contained in the Diet Coke and the gelatin & gum arabic ingredients of the Mentos all contribute to the geyser effect. In addition, the MythBusters theorized that the physical structure of the Mentos is the most significant cause of the eruption. When a flavored Mentos with a smooth waxy coating was tested in carbonated water, no reaction occured, whereas a standard Mentos added to carbonated water formed a small geyser, thus affirming the nucleation site theory.

According to this interview of the Mythbusters team, they conclude that plain table salt is more effective at creating the eruption than Mentos. Of course then it's not called a Mentos eruption, but if the most powerful eruption is desired, table salt may be the most effective agent to add to Diet Coke.

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Trivia

‹The template How-to is being considered for merging.› 

It is also possible to make a rocket using mentos in a carbonated beverage. To do so, you need about 7 mentos, duct tape, and of course the soda. Place the 7 mentos on the duct tape, tape it to the inside of the cap, screw the cap on tightly, shake up the bottle, and throw it against the ground. The pressure of the carbon dioxide will shoot out of whatever opening is made in the bottle, propelling it into the air. However, there is a chance that the bottle will not go in the air, but just shoot fizz out.

Citations

  • Spangler, Steve. "Mentos Explosion". Retrieved 2006-08-04.
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