I think everyone has seen a video of the Coke and Mentos Geyser, if they haven't tried it themselves (if you haven't seen a video you should go check one out!). Ever wondered how it works?

As you know, Coke is made up mostly of sugar (or sweetener), flavouring, water and preservatives. The thing that makes it fizzy is carbon dioxide gas (CO₂). Until the bottle is opened and you pour some Coke out, the gas mostly stays dissolved in the water and is surrounded by water molecules. If you shake the bottle, the gas is released from the protection of the water molecules and escapes once the bottle is opened, bringing some of the Coke with it. Dropping some Mentos into the Coke also helps the CO₂ gas to escape but how?

Water molecules strongly attract each other and link together very easily to form a mesh around each bubble of CO₂. This attraction is called surface tension. To form a new bubble or to make a bubble bigger, the water molecules have to push away from each other. Breaking the surface tension of water requires energy. Dissolving a Mentos in the Coke provides the energy needed and means that new bubbles can form.

Mentos sweets have hundreds of tiny pits all over the surface (see picture on right, taken from http://www.waynesthisandthat.com/mentos.htm showing the pits on the surface of a Mentos sweet) and these pits are perfect places for bubbles of CO₂ to form. Add all this to the fact that the Mentos sweets are heavy and sink to the bottom of the bottle and you have a recipe for a huge eruption.

When all the gas inside the bottle is released, all of the liquid is pushed up and out of the narrow neck of the bottle creating a huge geyser.

• Disclaimer
• Privacy
• Copyright
• Accessibility