氢氧化钠Sodium hydroxide

NaOH 是离子化合物，在水中完全电离为 Na⁺ 和 OH⁻，0.1 mol/L 溶液 pH 约 13。它能与酸中和、与酸性氧化物和两性物质反应，并使油脂皂化。溶解热约 −44.5 kJ/mol，配制浓溶液时需不断搅拌散热。玻璃中的 SiO₂ 会被缓慢腐蚀，因此盛放 NaOH 溶液的试剂瓶要用橡胶塞。

NaOH is ionic and dissociates completely in water into Na⁺ and OH⁻; a 0.1 mol/L solution has a pH of about 13. It neutralises acids, reacts with acidic oxides and amphoteric substances, and saponifies fats. Its enthalpy of solution is about −44.5 kJ/mol, so concentrated solutions must be stirred while dissolving. It slowly attacks the SiO₂ in glass, so bottles of NaOH solution are closed with rubber stoppers.

古代用草木灰（K₂CO₃）或纯碱与石灰乳反应制得苛性碱，用于制肥皂：Na₂CO₃ + Ca(OH)₂ → 2 NaOH + CaCO₃↓（苛化法）。1890 年代起改用电解饱和食盐水，现代采用离子交换膜法，同时得到氯气和氢气。全球年产量约 8000 万吨。

In the past caustic alkali was made from wood ash (K₂CO₃) or soda ash with slaked lime for soap making: Na₂CO₃ + Ca(OH)₂ → 2 NaOH + CaCO₃↓ (causticisation). From the 1890s brine electrolysis took over, and modern plants use ion-exchange membrane cells that also give chlorine and hydrogen. World output is about 80 million tonnes a year.

氢氧化钠用于造纸、制铝（拜耳法溶解铝土矿）、肥皂和洗涤剂、人造纤维、石油精制和水处理，也是疏通下水道的家用产品成分。它对皮肤和眼睛有严重腐蚀性，沾到皮肤上应先用大量水冲洗，再涂硼酸溶液。

It is used in paper making, aluminium production (dissolving bauxite in the Bayer process), soaps and detergents, rayon, petroleum refining and water treatment, and in household drain cleaners. It is severely corrosive to skin and eyes; wash any splash with plenty of water, then apply boric acid solution.