Potassium Hydroxide (Koh)

Topics: Potassium hydroxide, Sodium hydroxide, Potassium Pages: 5 (1663 words) Published: December 31, 2012
Potassium Hydroxide (KOH)
Potassium hydroxide is an inorganic compound with the formula KOH, 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 applications exploit its reactivity toward acids and its corrosive nature. In 2005, an estimated 700,000 to 800,000 tonnes were produced. Approximately 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. Other names are Caustic Potash, Potash Lye, Potassia or Potassium Hydrate. Properties

Potassium hydroxide can be found in pure form by reacting sodium hydroxide with impure potassium. Potassium hydroxide is usually sold as translucent pellets, which will 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, meaning the process gives off significant heat. Concentrated aqueous solutions are sometimes called potassium lyes. Even at high temperatures, solid KOH does not dehydrate readily. Other info is:- Physical Properties

1.Molecular formulaKOH
2.Molar mass56.1056 g/mol
3.Appearancewhite solid, deliquescent
5.Density2.044 g/cm3
6.Melting point406 °C, 679 K, 763 °F
7.Boiling point1327 °C, 1600 K, 2421 °F
8.Solubility in water97 g/100 mL (0 °C)
121 g/100 mL (25 °C)
178 g/100 mL (100 °C)
9.Solubilitysoluble in alcohol, glycerol
insoluble in ether, liquid ammonia
10.Acidity (pKa)13.5 (0.1 M)
11.Refractive index (nD)1.409
12.Crystal structurerhombohedral
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 dehydrate KOH•2H2O, and the tetra hydrate KOH•4H2O. Approximately 121 g of KOH will dissolve in 100 mL of water at room temperature (compared with 100 g of NaOH in the same volume). Lower alcohols such as methanol, ethanol, and propanols are also excellent solvents. The solubility in ethanol is about 40 g KOH/100 mL. 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: distillation of these basic liquids from slurry of KOH yields the anhydrous reagent. 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. Reactions

KOH is highly basic, forming strongly alkaline solutions in water and other polar solvents. These solutions are capable of deprotonating many acids, even weak ones. In analytical chemistry, titrations using solutions of KOH are used to assay acids. KOH, like NaOH, serves as a source of OH−, a highly nucleophilic anion that attacks polar bonds in both inorganic and organic materials. In perhaps its most well-known reaction, aqueous KOH saponifies esters: KOH + RCO2R' → RCO2K + R'OH

When R is a long chain, the product is called 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. Molten KOH is used to displace halides and other leaving groups. The reaction is especially useful for aromatic reagents to give the corresponding phenols. Complementary to its reactivity...
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