Coke and Aluminum

name        Michael
status       other
grade        other
location     AA

Question -   Hi,
    I have a 13 year old son doing a science fair project.  He is
working on the corrosive properties of Coke.  When he put aluminum
into the container of soda, it begins growing a green
mold.  Thinking that this may have been due to contaminated samples
he has redone the experiment 3 more times each time with the same result.
Is this a normal reaction?  What is the cause?  Could this have any health
risks?
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A couple of factors here. Most soda beverages contain a little phosphoric
acid in addition to the CO2 that causes the "fizz". Aluminum phosphate
rapidly forms a self-healing film of aluminum phosphate,
Al(PO4) which protects the aluminum from further oxidation by acid. So it is
possible that little reaction will occur. In addition, soda beverages
contain sugar, and acid-loving molds are everywhere. So unless special
precautions are taken, the molds and sugar in the Coke will just keep
re-infecting the system.

Vince Calder
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