MadSci Network: Chemistry

Re: VRD - nucleated sites/ wintergreen lifesavers

Date: Fri Feb 4 15:26:29 2000
Posted By: Kieran Kelly, Consultant, The Boston Consulting Group
Area of science: Chemistry
ID: 949614409.Ch

What a great experiment, Marcus!  The wintergreen mint is causing the 
carbon dioxide bubbles to form faster in the bottle than they would 
normally and escape from the beverage more quickly, which is how the geiser 
happens.  The term "nucleation" refers to the formation of (in this case) 
bubbles on a surface, where the mint is the 'site' and the nucleation is 
done by the CO2.  The same term can be used when you are describing crystal 
growth - you can add nucleation sites (non-reactive surfaces) to a 
super-saturated solution and trigger a physical change.  It sounds like the 
article didn't explain very well - it is really the mint that acts as a 
nucleation site for the carbon dioxide.  The soda does not 'activate the 
mint's nucleated sites'.

Almost anything you put into the soda will help the gas bubbles to escape 
faster because it gives the carbon dioxide bubbles more surface area on 
which to form, so the beverage will fizz more.  The rougher the surface 
(the more surface area) of the object you put in the soda, the faster the 
bubbles will form and the bigger your geiser.  The real question now 
is: which soda will make the better geiser - a cold one or a warm one?  
There are some clues in our Mad Science archives about CO2 solubility 
varying with temperature that might help you guess the answer.  ;)

Thanks so much for your question and for giving me a great experiment idea!


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