Potassium hydroxide

Potassium hydroxide is an inorganic compound with the formula KOH, and is commonly called caustic potash. Potassium hydroxide is an inorganic compound with the formula KOH, and is commonly called caustic potash. Along with sodium hydroxide (NaOH), this colorless solid is a prototypical strong base. It has many industrial and niche applications, most of which exploit its caustic nature and its reactivity toward acids. An estimated 700,000 to 800,000 tonnes were produced in 2005. About 100 times more NaOH than KOH is produced annually. KOH is noteworthy as the precursor to most soft and liquid soaps, as well as numerous potassium-containing chemicals. It is a white solid that is dangerously corrosive. Most commercial samples are ca. 90% pure, the remainder being water and carbonates. Potassium hydroxide is usually sold as translucent pellets, which become tacky in air because KOH is hygroscopic. Consequently, KOH typically contains varying amounts of water (as well as carbonates - see below). Its dissolution in water is strongly exothermic. Concentrated aqueous solutions are sometimes called potassium lyes. Even at high temperatures, solid KOH does not dehydrate readily. At higher temperatures, solid KOH crystallizes in the NaCl crystal structure. The OH group is either rapidly or randomly disordered so that the  OH− group is effectively a spherical anion of radius 1.53 Å (between Cl− and F− in size). At room temperature, the  OH− groups are ordered and the environment about the K+ centers is distorted, with K+—OH− distances ranging from 2.69 to 3.15 Å, depending on the orientation of the OH group. KOH forms a series of crystalline hydrates, namely the monohydrate KOH • H2O, the dihydrate KOH • 2H2O and the tetrahydrate KOH • 4H2O. Like NaOH, KOH exhibits high thermal stability. The gaseous species is dimeric. Because of its high stability and relatively low melting point, it is often melt-cast as pellets or rods, forms that have low surface area and convenient handling properties. About 121 g of KOH dissolve in 100 mL water at room temperature, which contrasts with 100 g/100 mL for NaOH. Thus on a molar basis, KOH is slightly less soluble than NaOH. Lower molecular-weight alcohols such as methanol, ethanol, and propanols are also excellent solvents. They participate in an acid-base equilibrium. In the case of methanol the potassium methoxide (methylate) forms: Because of its high affinity for water, KOH serves as a desiccant in the laboratory. It is often used to dry basic solvents, especially amines and pyridines. KOH, like NaOH, serves as a source of  OH−, a highly nucleophilic anion that attacks polar bonds in both inorganic and organic materials. Aqueous KOH saponifies esters: When R is a long chain, the product is called a potassium soap. This reaction is manifested by the 'greasy' feel that KOH gives when touched — fats on the skin are rapidly converted to soap and glycerol.