For years, scientists and laypeople alike have been startled by the dramatic effect created by dropping a package of Mentos candies into a 2-liter bottle of Diet Coke. Onlookers are rewarded with a fountain of bubbles and soda shooting up to 10 meters in the air. Through a variety of experiments, scientists have recently concluded how this fountain is created.
Bubble Growth
The surface area of Mentos candies is relatively rough and pitted. This rough surface encourages bubble growth when the water tension is interrupted. Water molecules tend to stick together. When Mentos are dropped into Diet Coke, they break apart the molecules and provide a good amount of surface area for bubbles to form on.
Surface Tension
Low surface tension encourages bubble growth. Researchers found that drinks sweetened with aspartame have lower surface tension than those without it. The size of the shooting fountain is due to a maximum amount of bubbles being created in the soda when they interact with the Mentos. It is for this reason that the reaction is more dramatic with Diet Coke than with regular Coke.
Gum Arabic
Mentos candies are coated with an sweetener called gum arabic, which is a surfactant. Studies have concluded that surfactants lower the surface tension in water, allowing more bubbles to grow. When gum arabic is paired with aspartame, also an agent-lowering surface tension, a dramatic amount of bubbles is produced.
Sinking Candies
Mentos are dense candies. They sink quickly when dropped into a bottle of soda. This creates a great amount of exposure to the liquid, and quickly. Mentos gather bubbles quickly, release them and gather more as they sink. When experimented with, crushed Mentos fell more slowly and therefore the spout of soda created was dramatically smaller. With whole Mentos, the bubble creation happens so rapidly that it causes the soda and bubbles to shoot dramatically up and out through the hole in the bottle.
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