Following in the footsteps of the first post on this blog, I though I would point out another popular misconception: You cannot make explosives out of soap – despite this process being crucial to the plot of “The Legend of Zoro”. I’ve heard this myth in various forms over the past year, usually it is soap, but I have also heard that one can make explosives from biofuel. It is essentially the same issue in both cases. I guess this myth irks me in particular because it is a misunderstanding of one of the most simple and widespread chemical reactions there is.
So, making soap is pretty easy, it is the same principle as an acid/base reaction. Just mix some fat and some inorganic base (say sodium or potassium hydroxide) and the metal ions displace the glycerol in the fat giving soap and glycerol (glycerin).
How to make soap. From Wikipedia: Saponification - Fat (left), Base (on arrow), Soap (inner right), Glycerol (far right)
Some more detail…
Fats are tri-glycer-ides which means “three bits stuck to a glycerol molecule”. The saponification processes is the breaking off of these three bits (the fatty acids), which become the soap (fatty acid salts), leaving glycerol. As a word equation:
Fat + Base 
or, in the very similar case of (base catalyzed) biodiesel production. In this case there is a load of methanol (MeOH) not base (NaOH, KOH):
Fat + Methanol
It is fairly easy (though very dangerous) to make an explosive (nitroglycerin) from the glycerol byproduct by nitration, this is undoubtedly where the myth comes from. But somehow the understanding of this reaction has reached the masses as “you can make a bomb out of soap/biofuel” – which you can’t: You can make a (shit – if you like your limbs) bomb out of a byproduct of soap production.
End Of Rant.
