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Soap: RCOONa — sodium salt of long-chain fatty acid (C12-C18). Made by saponification (fat + NaOH → glycerol + soap). NaOH → hard soap (bars); KOH → soft soap (liquid). Cleaning mechanism: In water above CMC, soap forms micelles (hydrophobic tails in, hydrophilic COO- heads out). Grease dissolves in hydrophobic core → emulsified → washed away. Hard water problem: 2RCOONa + Ca2+ → (RCOO)2Ca (insoluble scum) → wastes soap, leaves residue. Detergent: R-OSO3Na (sodium alkyl sulfate) or R-C6H4-SO3Na (sodium alkylbenzene sulfonate). Made from petroleum. Same micelle cleaning mechanism as soap. Advantage: Ca/Mg salts are SOLUBLE → no scum → works in hard water. Environmental concern: Branched-chain detergents (hard) are non-biodegradable → foam pollution in water. Linear-chain detergents (soft) are biodegradable → bacteria metabolize straight chains. Most countries now mandate soft detergents. Both soaps and detergents are surfactants (surface-active agents) that lower water's surface tension, enabling wetting and cleaning. JEE tests: soap vs detergent in hard water, biodegradable vs non-biodegradable, saponification reaction, micelle structure.