Senku's Soap
In Dr Stone
Senku undertakes to make soap for the basic comfort of Kohaku’s village. He uses wood ash and animal fat — a process known to humanity for millennia. This invention is one of the first real victories of the nascent “kingdom of science”.
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