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Q.What are soaps? How are soaps prepared? Define antiseptic.

Maharashtra MsbshseMaharashtra HSC (MSBSHSE) Board 2020Subjective· 3mImportance★★★★★
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Soaps are fatty-acid salts made by boiling fats with alkali; antiseptics are microbe-killing chemicals safe for skin/wounds.

Soaps: Soaps are sodium or potassium salts of long-chain (C12–C18) fatty acids, e.g. sodium stearate, C17H35COONaC_{17}H_{35}COONa.

Preparation (saponification): Natural fats/oils (glyceryl esters of fatty acids) are boiled with concentrated aqueous NaOH solution; the ester bonds hydrolyse to give the sodium salt of the fatty acid (soap) plus glycerol:

(C17H35COO)3C3H5+3NaOH→boil3C17H35COONa (soap)+C3H5(OH)3 (glycerol)(C_{17}H_{35}COO)_3C_3H_5 + 3NaOH \xrightarrow{boil} 3C_{17}H_{35}COONa\ (soap) + C_3H_5(OH)_3\ (glycerol)

The soap is then precipitated out of solution by adding common salt (NaCl) — a process called 'salting out' — and is separated, purified and moulded into cakes.

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