Final answer:
Saponification is the chemical reaction where alkali from wood ash interacts with triglycerides in fat to produce soap and glycerol. The alkali replaces the glycerol in the triglyceride, creating soap molecules which are the sodium or potassium salts of fatty acids.
Step-by-step explanation:
The process by which the alkali of the ash replaces the glycerol of the triglyceride to form soap is known as saponification. During this reaction, triglycerides, which are esters of fatty acids and glycerol, undergo hydrolysis in the presence of a base, typically sodium hydroxide (NaOH) or potassium hydroxide (KOH). The alkali acts on the fat, cleaving the fatty acids from the glycerol backbone and forming the sodium or potassium salts of the fatty acids, which are the soap molecules. Glycerol is released as a byproduct. Traditionally, this alkali was obtained from wood ashes containing potassium carbonate (K2CO3).