How is soap made? The saponification chemistry of Dr Stone
In Dr Stone
Soap is one of Senku’s very first creations: early in the series, he lists it among the uses of the calcium carbonate he gets from seashells (along with fertilizer and mortar), back when he is surviving alongside Taiju, one of the demonstrations that reveal his scientific potential to Tsukasa. Later, in Kohaku’s village, that soap resurfaces in the bubble scene that leaves Kinro and Ginro dumbfounded: Senku’s “sorcery” is just chemistry, wood ash and animal fat, a process humanity has known for millennia.
The subject in depth
Triglycerides (fats) react with a strong base, typically sodium hydroxide (NaOH) or potassium hydroxide (KOH), extractable from wood ash, to yield a fatty-acid salt (the soap proper) and glycerol. The soap molecule is amphiphilic: its polar head loves water, its carbon tail loves fats. That is what allows it to “dissolve” greasy dirt into water.
Deeper into the mechanism: the nucleophilic attack of the hydroxide ion on the carbonyl ester carbon releases glycerol and forms the carboxylate anion, which pairs with the cation to form the salt, the soap. Soft soaps (potash-based) stay pasty at room temperature; hard soaps (lye) solidify. Above a certain concentration (the critical micelle concentration, CMC), molecules aggregate into micelles that trap oils inside.
Going further
- Saponification, cross-cutting concept entry
- Discipline: Chemistry, all chemistry entries on the site
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