Mentos eruption

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A Mentos eruption (also known as a Mentos and Diet Coke geyser or Soda 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 diet cola, resulting in an eruption. This reaction is thought to occur because of rapidly expanding carbon dioxide inside once the Mentos are introduced to the carbonation.

[edit] 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.<ref name=spangler>Spangler, Steve. Mentos Explosion. Retrieved August 4, 2006.</ref> 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.<ref name=spangler/>

When Mentos are 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 its surface. These tiny pits function as nucleation sites, perfect places for carbon dioxide bubbles to form. As soon as the Mentos enter the soda, bubbles form all over their surface. They quickly sink to the bottom, causing carbon dioxide to be released by the carbonated liquid with which they come into contact 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 flavored Mentos with a smooth waxy coating were tested in carbonated water, no reaction occurred, whereas standard Mentos added to carbonated water formed a small geyser, thus affirming the nucleation site theory. This was further supported when rock salt was used as an effective substitute for Mentos.