There’s a problem with the Coke & Mentos experiment that few people know about and we want to share it with you! Check you’ve got the right ingredients, follow our tips and then there’s something else you should consider.


Since 2005 the Coke & Mentos reaction has been wow-ing children and adults everywhere – when it goes well! Drop several Mentos into a bottle of coke or lemonade, and a huge eruption of bubbles shoots out several meters high. This is what is meant to happen, but often it fails and the geyser isn’t quite as impressive as seen in the videos.

You can get a super-high geyser, but first, check you’ve got the right kit:

  1. It’s important to use Mentos Mints with the right drink – coke or lemonade are the best (not carbonated water for example)
  2. Drop in at least 5 mints at once – too few and the reaction is less impressive.
  3. Ensure you use a 2L bottle of drink, smaller bottles don’t work – they don’t have enough CO2 in them to make a good geyser.
  4. Diet drinks are slightly better than regular ones because you won’t get covered in a sticky sugary mess, and also they explode higher as they are less viscous.

So, you’ve got the right kit, but still are not getting a huge explosion every time?
Have you thought about the temperature of the drink?

Aha!!

Temperature is really important in this experiment, but is rarely mentioned in how-to guides. In our investigation we found that cold bottles of coke and lemonade produce a very poor geyser and the reaction is much slower compared to drinks that are at room temperature.

Check out our image below, and yes, Mentos were dropped in at the same time!! The drink on the right had just come out of the fridge (we cooled the Mentos too), and the one on the left was at room temperature – what a difference!

exploding bottles of Coke & Mentos

 

We made a video too….don’t pick a lemonade fight with a kid, you’ll always lose!

Why does temperature matter?

At warmer temperature CO2 gas particles (and other molecules) have more energy, they move faster and want to escape the liquid they are dissolved in quickly compared to cooler temperatures. When its warmer, gas doesn’t dissolve well in liquids and is more liable to escape from a liquid it is dissolved in (this is called Henry’s Law). Try cracking open a can of warm fizzy drink and compare it to one just from the fridge!

 

How does the Coke & Mentos reaction work anyway?

A 2 Litre bottle of coke or lemonade have 8 litres of CO2 dissolved in them. Have you noticed, your fizzy drink has tiny bubbles appearing on the side of the glass at a particular spot? This is because bubbles form on tiny pits on the surface of a container. These imperfections are called nucleation sites. On your glass, there are fine imperfections which act as nucleation points where the bubbles can form and escape. Mentos have hundreds of tiny imperfections (nucleation sites) on their surface. Dropping Mentos into coke or lemonade allows the dissolved gas within the liquid to come out of the liquid super-fast at these nucleation points on the Mentos surface. Thus the Coke and Mentos reaction is a physical one, not a chemical reaction.

 

Want more easy science guides?

Head on over to our blog to find out other cool experiments such as Glowing Fluorescent Liquid or the Super Easy 6 – a free download with 6 super-easy experiments to try at home!

You can also check out the workshops we have coming up in Devon, why not book on?

If you try these activities at home you do so at your own risk.

Happy science-ing

Ruth

Chief Scientist

Sciencedipity