- Jan 20, 2010
- Reaction score
Almost right. Couple of points you may have overlooked. First, is that when soap is first made, and for the first couple of days it's still got quite a lot of unreacted lye available. So, your batch wrapped up for transport, especially if it was soft enough to slosh, had very much enough lye available to cause a really nasty reaction with the foil if they had come into contact. Second, is that the pH of soap never does approach neutral, it stays very firmly on the alkaline side. I don't know what effect, if any, that would have on the solubility of aluminum, but it should probably be taken into account.
Aluminum likes to form aluminates in alkaline conditions. Certainly it's going to react badly with any remaining lye, but you'll also get sodium aluminate in any alkaline environment.
I don't know the strength of the reaction at soap pH, but it should be non-negligible. This article shows the rates just from a few food items in aluminum cookware:
And since you can use aluminum and baking soda to strip the oxidation from silver in seconds...well, I would advise limiting aluminum exposure to soap!