Australia's Science Forum

Sorry for all the questions... but here's another few...

I know it has been said that diet coke works the best, so I have 2 options for experiments:

Option 1 - use all diet coke and test the difference between quantity of mentos added (eg. 2, 4, 6, 8, 10)

Option 2 - use all different cokes (Coke, diet coke, vanilla diet coke, caffeine free diet coke and coke zero) and see which one works best (and then have a hot one with frozen mentos to finish off - read that somewhere here on Chemtalk)

Is it right that it is the blue packets that work best, and not the fruity ones?

Thanks again for all your help and ideas everyone!!

Rosalie,

The Diet Coke is a MUST. Mythbusters did a fantastic report on this, where they broke down Diet Coke into it's component parts. They tested just soda water, then soda water with caffeine, soda water with coke flavouring (caramel), and soda water with the artifical sweetener (aspartame). It was the best ever example of fair testing that I have seen on TV. The ultimate result is that it is the combination of artifical sweetener, preservative and caffeine in the soda water that gives the best results.

They also explained the need for mint mentos (the blue packet). It is because the whole explosion is caused by the rapid catalysing of all the CO2 out of the coke. The roughened surface of the mint lollies prvides multiple "sites of nucleation" where the CO2 was forced out of solution. The gelation and gum arabic in the lollies also contribute to the rapidity of the effect.

I've also tried it with a test tube full of salt, and had fairly good results, which proved that in essence providing multiple sites of nucleation is the aim here.

BTW ProfBunsen sells a groovy doovy rig for the whole experiment, for not much money.

Good luck.

So I'd be better off experimenting with the number of mentos rather than the types of coke?

Do the other types give any reaction at all?

I don't have time (or money!) to do the whole thing before tomorrow. I just want to give the kids an idea of how to conduct an experiment and have some fun. Their class unit at the moment is 'Froth and Bubbles' which is why I am doing all this for them.

Thanks again

Hi Rosalie
A whole packet of mentos fits in a large test tube 150mmx24mm. Put a microscope slide over the top of the test tube. Invert the tube and slide over the bottle opening. Then all you have to do is pull the slide out and the mentos drop in to the bottle. Oh and run!

Oh Dime that's such a good idea! I have my other contraption sorted now though It has a smaller hole so hopefully a higher fountain

And I forgot to mention, Smiley, that I looked at the one from Prof Bunsen but the postage was going to make it too expensive. I have modelled my homemade one on that one.

Rosalie

I use the same method as dime, the large (50ml) test tube and glass cover from gas jars.
To test a variable, use temperature. Do one bottle of diet coke (and yes, must be a 2l bottle of diet coke) that has been in the fridge, one at room temperature and one that has been sitting in a bucket of very hot water. It's a great demonstration of how reactivity rates increase with heat.

Cool! I am so suggesting that to my teachers! Plus we get to play outside.

when needing hydrogen peroxide in a hurry hairdressing suppliers have it - Priceline have it very cheap.

Hope that is of some help to those who want it in a hurry

Question about the heated diet coke - do you heat it with or without the lid on?

I am eagerly awaiting the delivery of my 35% hydrogen peroxide (rang a few carpet cleaners - no luck there :( ) so I can practice the elephant's toothpaste for tomorrow. I hope it arrives in time! I ordered it on Monday...

Tips for the Diet Coke:

1. Heat it by placing it lid on in a bucket of very hot water. Otherwise you drive off all the CO2 before you get to explode them.
2. Have all your cokes outside and sitting down (yes the cokes not the kids) before the experiment, so they have time to settle. If you get little cherubs to help carry stuff down the coke will be a shaken up before you open them, thus defeating the purpose, as they fizz up when you open them just from being shaken about.

re the Hydrogen Peroxide. I actually got onto the carpet cleaners via my cleaning supplies place. They sell it, but only in 20L drums. So they actually put me onto a couple of their end users, seeing as how it's not exactly a trade secret or anything. You could try asking local cleaning supply companies. And beware the hairdressers. Last time a salon said "yes yes we have some", it turned out to be already mixed with a conditioner, so it wasn't what we needed. Hospitals also carry H2O2. They have to use it on motorbike accidents victims, to bubble out all the gravel that is usually embedded in their thighs after a crash. Gives one the shudders just to think of it, but it works.

We have never had much luck doing the Diet coke and Menthos. Do you use the menthos straight from the pack or do you crush them a little to get more surface area. I read somewhere that the Australian menthos had a smoother surface so didn't work as well.

Using my little contraption I made last week I got the fountain as high as a house roof in my trial before doing it for the kids. But when I did it for the kids the mentos got stuck in the tube and blocked it meaning a fine spray came out instead :( most disappointing for me but still exciting for the kids (they didn't know what was supposed to happen). I am going to do it again tomorrow without my contraption (which I made intending to get a higher fountain than you'd get just through the opening of the bottle) and also do the elephant's toothpaste. Hopefully I'll get some photos and post them here for you

Another tip for the heated up diet coke is to open the lid VERY SLOWLY!