Potassium:
Kalium. K; at. wt. 39.0983; at. no. 19. valence 1. Alkali metal. Occurence in earth's crust: 2.59% by wt. Natural isotopes: 39 (93.22%); 40 (0.012%); 41 (6.77); 40K is radioactive: T 1.26 x 109 years; isotopes range mass number from 37 to 47. Found mainly as teh chloride (sylvite); also in the aluminosilicates orthoclase, and microcline (KAlSi3O8), and as carnallite (KCl.MgCl2.6H2O). First prepd in free form by Davy in 1807 by electrolysis of fused potassium hydroxide. Prepns: Hackspill, Helv. Chim. Acta 11, 1003 (1928); Jackson, Werner, U.S. pat. 2,480,655 (1949 to Mine Safety Appliances Co.). NMR Spectrum of potassium anion (K-): P.P. Edwards et al., Nature 317, 242 (1985). Review: Whaley, "Sodium, Potassium, Rubidium, Cesium, and Francium" in comprehensive Inorganic Chemistry vol. 1, J.C. Bailar, Jr. et al., Eds (Pergamon Press, Oxford, 1973) pp 369-529; J.S. Greer et al., in Kirk-Othmer Encyclopedia of Chemical Technology vol. 18 (Whiley-Interscience, New York, 3rd ed., 1982) pp 912-920.

Soft, silvery-white metal; body-centered cubic structure; tarnishes on exposure to air; becomes brittle at low temps; mp 63.2. bp 765.5; d20 0.856. Specific heat (0): 0.176 cal/g deg. Thermal conductivity (cal /sec C cm): 0.23 (21); 0.956 (400). Sol in liq ammonia, ethylenediamine, aniline; sol in several metals, forming alloys. One of the most active metals; E (aq) K/K+ 2.922V. Reacts vigorously with oxygen; with water even at -100; with acids; with the halogens, igniting with bromine and iodine. Molten metal reacts with sulfur; with hydroten sulfide. Reacts with hydrogen slowly at 200, rapidly at 350-400. Reacts slowly with anhydr hydrogen halides at room temp; molten metal ignites in the reaction. Reduces silicates, sulfates, nitrates, carbonates, phosphates, oxides and hydroxides of the heavy metals, often with the separation of the metal. Reacts with organic compds containing active groups. Inert to saturated aliphatic and tho aromatic hydrocarbons. Keep under liquid containing no oxygen, e.g., liquid petrolatum, petroleum, etc.

USE: In synthesis of inorganic potassium compds; in organic syntheses involving condensation , dehalogenation, reduction, and polymerization reactions. As heat transfer medium together with sodium: Chem. & Eng. News 33, 648 (1955).
Ref.: 7579, 1211 pp.
The Merck Index - Eleventh Edition.
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