Our kids have been born to parents who both have a science background. It’s something we’d like to share with them so what better than simple experiments with easily obtainable materials and easily observed results.
The plan was to have fun, make a mess and hopefully introduce a few science concepts. To that end we decided to start with the classic mentos into coca cola experiment.
Before starting we asked the kids what they thought would happen. Tilly decided that it would ‘go all fuzzy and stuff would explode out’ and Lex thought that ‘air pressure in the bottle would push the cola out’. There is a slight possibility that they may have been doing some sneaky Googling beforehand…
Materials: tube of mentos mints, 2 litre bottle of coca cola (diet or regular, although diet apparently gives better results regular was the version on sale near us) and a tube the diameter of the mentos tube to facilitate rapid deployment of the mentos into the coke (we just used a bit of cardboard from an Amazon delivery box held together with tape.
- Fill the cardboard tube with mentos, using a bit of cardboard taped across the bottom to stop them from falling out.
- Go outside.
- Find a level piece of ground in an area (at least a few metres square) that you don’t mind getting messy.
- Open the cola bottle, empty the tube of mentos into it and move away quickly!
- Watch what happens.
Sadly I didn’t manage to capture the most impressive part of the resulting geyser with my camera but it was somewhere between 2 and 3 metres high which was pretty cool.
The kids were pretty excited by the outcome of the experiment. We then looked at what was left over, measuring the remaining coke (only 600 ml) and investigating the mentos which ‘looked like they’ve been sucked!’.
The Science Bit
So why does it happen? Well, it’s all to do with the carbon dioxide gas in the coke. To make the coke fizzy this is added to the liquid and pressurised, the surface tension of the coke liquid then stops the gas bubbles from expanding (holds them in place). When we add the mentos the gas bubbles cling to them (just as they would do to a straw in a glass of fizzy drink) and when the outer coating dissolves the surface tension is disrupted. This disruption allows the gas molecules to expand and push the liquid molecules out of the way. The liquid has nowhere to go but out of the bottle and the expansion is so rapid and forceful that whoosh there goes a geyser.
For a more detailed description try: Steve Spangler Science – Mentos Diet Coke Geyser
Our kids gave this experiment two thumbs up – although considering it involves an explosion I’m not sure there could have been any other outcome!
Things to note if you’d like to try this yourself:
- you need an unopened (before the experiment) bottle of coke – you want as much carbon dioxide in the bottle as possible
- it does need to be coke (not just own brand cola) if you want a decent geyser although you could use different types if you wanted to let the kids add some variables into the experiment
- you really need to be able to get the mentos into the bottle quickly – take a little bit of time to make sure your cardboard tube is the right size