Thursday, 20 August 2009 13:48

We all know about the brilliant Diet Coke and Mentos experiment right? Simply drop some regular Mentos sweets into a bottle of Diet Coke, stand back, and boom – you’ve got yourself a gloriously sticky foam fountain! But how does it work?

The video (with over 9million YouTube hits!!) shows the EepyBird guys performing some stunning displays, all thanks to a bit of cool science

If you want to try it for yourself Steve Spangler has some great advice here.

So, the interesting question is why does it work. Exactly why Coke and Mentos produce these awesome eruptions is still a much debated topic. Scientists are still wracking their brains on what is precisely going on in that bottle of fizz. For example, there is debate about why diet cola works better than regular. Is it the artificial sweetener? The jury’s out. One good reason for using diet drinks however is that they are less sticky and messy to clean up! We’ve checked out the theories and this is what we think:

The gas that makes Coke fizzy is called Carbon Dioxide - CO2. All that CO2 is trapped in the liquid inside the bottle and is held in place by the pressure and the surface tension of the water in the Coke (water molecules are attracted to each other and they form almost a net that keeps the CO2 molecules in place in the Coke, stopping them from turning into a gas).

If you shake the bottle and open the lid all that CO2 will escape from the water as gas, usually taking some of the coke along with it.

There is also another way to release the CO2. If you provide somewhere for the CO2 bubbles to grow then they can then escape as gas. And these places are called nucleation sites.

That’s one of the secrets of Mentos: They're covered in lots of little pits that act as these nucleation sites. When you throw a tube of Mentos into the Coke loads of bubbles form in these pits creating a whole load of gas that rushes to escape the bottle producing your characteristic eruption. Plus, the other secret is that Mentos are covered in a layer of gelatin and gum arabic that dissolves in the water, breaking down some of that surface tension. This means that the CO2 can be released ever easier!

Also check out the Mythbusters talking about the Diet Coke & Mentos messiness here and their competition to make the highest eruption here.

Science: So What? will be bringing you a whole host of DIY experiments you can try at home. While we scurry around to collect all these why not have a look at our DIY Science page. Plus, there are loads more fun science experiments performed on the  Planet SciCast videos.

Related links

Diet Coke and Mentos fizz or flop article

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swanc

Nov 13

Has anyone tried this themselves?

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