sodium hydroxide(redirected from Naoh)
Also found in: Dictionary, Thesaurus, Medical, Acronyms.
(caustic soda, soda lye), NaOH, a caustic alkali; colorless crystals. Density, 2.13 g/cm3; melting point, 320°C. The industrial product is an opaque, white solid mass with a radial fracture. Sodium hydroxide is hygroscopic; a large amount of heat is liberated upon its reaction with water. Aqueous solutions of NaOH exhibit a strong alkaline reaction. The solubility of sodium hydroxide in water is 52.2 percent at 20°C and 75.8 percent at 80°C. It forms crystal hydrates, such as NaOH-H2O, which is stable at ordinary temperatures (12.3°-61.8°C). Upon exposure to air, NaOH absorbs CO2 and is converted into sodium carbonate. Sodium hydroxide has a destructive effect on skin, paper, and other materials; even very small quantities of NaOH cause extremely severe damage upon contact with the eyes.
Sodium hydroxide is prepared by electrolysis of NaCl solutions or by boiling a Na2 CO3solution with milk of lime: Na2C03+ Ca (OH)2 CaC03+ 2NaOH. The sodium hydroxide solution is evaporated, and the residue is heated to the melting point and then poured into molds. Electrolysis yields chlorine in addition to NaOH. Sodium hydroxide is one of the main products of the modern chemical industry; it is widely used both in the chemical industry and in many other sectors.