Soaps: Sodium/potassium salts of long-chain fatty acids. Sodium stearate = CH3(CH2)16COONa. Made by saponification: fat/oil + NaOH → glycerol + soap.

In water, soap forms micelles (spherical aggregates): hydrophobic tails point inward (away from water), hydrophilic COO- heads point outward (toward water). Grease/oil dissolves in the hydrophobic interior → emulsified → washed away.

Hard water problem: Ca2+ and Mg2+ ions react with soap → insoluble precipitate (scum): 2RCOONa + CaCl2 → (RCOO)2Ca (precipitate) + 2NaCl. This wastes soap and leaves residue on clothes/surfaces.

Detergents: Sodium alkyl sulfates (CH3(CH2)11OSO3Na — sodium lauryl sulfate) or alkylbenzene sulfonates (CH3(CH2)11C6H4SO3Na). Their calcium/magnesium salts are SOLUBLE → no scum in hard water.

Biodegradability issue: Linear chain detergents (soft detergents) are biodegradable — bacteria can metabolize straight chains. Branched chain detergents (hard detergents) are non-biodegradable — branching blocks enzymatic degradation → persist in water → foam pollution.