Sodium hydroxide

Sodium hydroxide, commonly known as caustic soda, is one of the most-used strong bases in the world — about 80 Mt produced annually, almost entirely via chlor-alkali electrolysis. This route is what couples its production to chlorine: the same NaCl-brine electrolysis cell simultaneously produces Cl₂ at the anode and NaOH + H₂ at the cathode. The fixed co-production ratio — ~1.1 t Cl₂ per 1 t NaOH — creates recurring imbalances on global markets: when chlorine demand (PVC, disinfectants) drops, NaOH becomes temporarily abundant and cheap, and vice versa.

NaOH applications span all industrial chemistry. The Kraft pulping process (~30 % of consumption) mixes it with Na₂S to break down lignin in wood and release cellulose fibres. The Bayer process (15 %) uses it at 220 °C and 30 bar to selectively dissolve alumina from bauxite, a key step in aluminium production. Saponification of fats (reaction NaOH + fatty ester → soap + glycerol) is the oldest domestic process — it dates from Babylon in -2500. Today, NaOH also intervenes in wastewater treatment, semiconductor etching and fine organic chemistry.

Handling: pure NaOH is a hygroscopic white solid that rapidly absorbs atmospheric moisture, and its dissolution in water is strongly exothermic (+44 kJ/mol) — hence the safety rule "always add acid to water, never the reverse" which applies symmetrically to concentrated bases. Skin contact triggers saponification of cutaneous lipids and deep burns that are sometimes initially painless (saponification of nerve receptors), making the injuries deceptive.