Chai Brady
Children’s Corner
A very popular experiment which always delivers quite spectacular results is the Diet Coke and Mentos geyser. It’s a lot of fun and sure to amaze your friends and family (assuming you do it outside rather than inside your house).
Apparatus
– Large bottle of Diet Coke
– About half a pack of Mentos
– Geyser tube (optional but makes things much easier)
Method:
Make sure you are doing this experiment in a place where you won’t get in trouble for getting Diet Coke everywhere. Outside on some grass is perfect, please don’t try this in your living room!
Stand the Diet Coke upright and unscrew the lid. Put some sort of funnel or tube on top of it so you can drop the Mentos in at the same time (about half the pack is a good amount).
Time for the fun part, drop the Mentos into the Diet Coke and run! If you’ve done it properly a huge geyser of Diet Coke should come flying out of the bottle, it’s a very impressive sight. The record is about nine metres (29 feet) high.
What’s happening? The thing that makes Coke fizzy is the carbon dioxide that is pumped in when they bottle the drink at the factory. It doesn’t start leaving the liquid until you open the lid (more if you shake it up beforehand). This means that there is a lot of carbon dioxide gas just waiting to escape the liquid in the form of bubbles.
In the Diet Coke bottle the Mentos provide a rough surface that allows the bonds between the carbon dioxide gas and water to break more easily, helping to create carbon dioxide bubbles. As the Mentos sink in the bottle, it causes the production of more and more carbon dioxide bubbles, and the rising bubbles react with carbon dioxide that is still dissolved in the soda to cause more carbon dioxide to be freed and create even more bubbles, resulting in the eruption.
Because Mentos are rather dense, they sink rapidly through the liquid, causing a fast, large eruption.
The experiment works better with Diet Coke than other carbonated drinks due to its slightly different ingredients and the fact that it isn’t so sticky. Diet Coke that has been bottled more recently works better than older bottles that might have lost some of their carbon dioxide sitting on shop shelves for too long, just check the bottle for the date.