Nomenclature
CAS number: 7440-09-7
Kalium.
Description and references
K; at. wt 39.0983; at. no. 19; valence 1.
Group IA (1). Alkali metal. Occurrence in earth's crust: 2.59%
by wt. Naturally occurring isotopes: 39 (93.26%); 40 (0.012%); 41
(6.73%); 40K is radioactive: T 1/2 1.27 × 109 years; known isotopes range in mass number from 35 to 54.
Found mainly as the chloride (sylvite); also in the aluminosilicates orthoclase, and microcline (KAlSi3O8), and as carnallite (KCl.MgCl2.6H2O). Major essential
element for plant growth. First prepd in free form by Davy in 1807
by electrolysis of fused potassium hydroxide. Produced industrially
by chemical reduction. Prepns: Hackspill, Helv. Chim. Acta 11, 1003 (1928); Jackson,
Werner, US 2480655 (1949 to Mine Safety Appliances Co.). NMR spectrum of potassium
anion (K-): P. P. Edwards et al., Nature 317, 242 (1985). Reviews: 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; Chemistry
of the Elements N. N. Greenwood, A. Earnshaw, Eds. (Pergamon
Press, New York, 1984) pp 75-116; K.-W. Chiu in Kirk-Othmer Encyclopedia of Chemical Technology vol. 19 (Wiley-Interscience, New York, 4th ed., 1996) pp 1047-1057.
Properties
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 liquid ammonia, ethylenediamine, aniline; sol
in several metals; forms liquid alloys with other alkali metals.
Emits characteristic violet color (766.5 nm) in flame. One of the
most active metals; E0 (aq) K/K+ 2.922 V. 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 hydrogen 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 to aromatic hydrocarbons. Dangerous when wet. Keep under liquid containing no oxygen, e.g.,
liquid petrolatum, petroleum, etc.Caution
Direct contact with metal may be
corrosive and cause skin and eye burns. See: Fire Protection Guide to Hazardous Materials (National Fire Protection Assoc., Quincy, MA, 12th ed., 1997) Section
49, p 109.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).
Radioactive decay of
40K to
40Ar used as tool
for geological dating.