JEE Main 2023 · 10 April · evening · Single correct · +4 / −1
The reaction used for preparation of soap from fat is :
- (a) an addition reaction
- (b) alkaline hydrolysis reaction
- (c) reduction reaction
- (d) an oxidation reaction
Answer and solution
Answer (b) alkaline hydrolysis reaction
Solution
Chemistry ma’am · 4 steps
A fat is an ester, and soap is made by breaking that ester with NaOH: that is saponification.
- What a fat is. A fat or oil is a triglyceride: an ester of glycerol with three long-chain fatty acids such as stearic acid, C₁₇H₃₅COOH.
- Boil with alkali. Heating the fat with aqueous NaOH splits each ester bond using water and base. This gives glycerol and the sodium salts of the fatty acids, and those salts are the soap.
(C₁₇H₃₅COO)₃C₃H₅ + 3NaOH → 3C₁₇H₃₅COONa + C₃H₅(OH)₃
- Name the reaction. An ester is broken by water in the presence of a base, so this is alkaline hydrolysis, also called saponification. Nothing is added across a double bond, and no carbon changes its oxidation state.
- So. Soap is prepared from fat by alkaline hydrolysis, option (b).
The idea to keep. Saponification means ester plus NaOH gives a carboxylate salt plus alcohol. For fats, that salt is soap and the alcohol is glycerol.
Answer from the NTA final answer key. Solution by PrepWiser.