Making Lots of Bubbles
After a lot of debate, scientists are now saying that the primary cause of Coke & Mentos geysers is a physical reaction, not a chemical reaction. Their explanation is this process called nucleation.
After a lot of debate, scientists are now saying that the primary cause of Coke & Mentos geysers is a physical reaction, not a chemical reaction. Their explanation is this process called nucleation.
All the carbon dioxide in the soda – all that fizz – is squeezed into the liquid and looking for a way out. It’s drawn to any tiny bumps that it can grab onto. Those tiny bumps are called nucleation sites: places the gas can grab onto and start forming bubbles.
Nucleation sites can be scratches on a glass, the ridges of your finger, or even specks of dust – anywhere that there is a high surface area in a very small volume.
The surface of a Mentos is sprayed with over 40 microscopic layers of liquid sugar. That makes it not only sweet but also covered with lots and lots of nucleation sites.
In other words, there are so many microscopic nooks and crannies on the surface of a Mentos that an incredible number of bubbles will form around the Mentos when you drop it into a bottle of soda.
Since the Mentos are also heavy enough to sink, they react with the soda all the way to the bottom. The escaping bubbles quickly turn into a raging foam, and the pressure builds dramatically.
All that pressure has got to go somewhere, and before you know it, you've got a big geyser happening!
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