piccadillyst
piccadillyst t1_irnrw3m wrote
Reply to comment by taphead739 in Why, when you continue to burn ash, do the ashes eventually change from black to white? by genitalwaffles
Interestingly, most of these are basic oxides, meaning that they form very alcaline solutions in water. This was exploited in ancient times to prepare soap from fat.
piccadillyst t1_irnxpe0 wrote
Reply to comment by l3lindsite in Why, when you continue to burn ash, do the ashes eventually change from black to white? by genitalwaffles
It's important not to mix up terms here. What you get after combustion are oxides: Na2O, CaO, K2O, MgO, etc (probably some superoxides as well, but I digress). These are not oxidants, because the metals are in very stable oxidation states. But they are very reactive towards water: the oxide anions "steal" protons from water, giving hydroxide ions as product. Specifically, in the case of K2O, the reaction would be something like: K2O + H2O ➡️2K+ + 2OH-. The hydroxide ions then react with triglycerides in the saponification reaction.