Title: Lanthanum
CAS Registry Number: 7439-91-0
Literature References: La; at. wt 138.90547; at. no. 57; valence 3. Group IIIB (3). A rare earth metal; member of the lanthanide series. Naturally occurring isotopes (mass numbers): 139 (99.91%); 138 (0.09%), radioactive, T½ 1.06 ´ 1011 years; known artificial radioactive isotopes: 123-137; 140-149. Estimated abundance in earth's crust: 18-35 ppm. Found in association with cerium and other light lanthanons. Sources of commercial importance are the rare earth minerals monazite and bastnaesite; also found in cerite. Discovery and isoln: Mosander, Pogg. Ann. 47, 207 (1839). Sepn: James, J. Am. Chem. Soc. 34, 757 (1912). Prepn of metal: Mazzi, Atti X Congr. Int. Chim. 3, 604 (1938); Spedding et al., Ind. Eng. Chem. 44, 553 (1952). Toxicity study: Cochran et al., Arch. Ind. Hyg. Occup. Med. 1, 637 (1950). Reviews of prepn, properties and compds: The Rare Earths F. H. Spedding, A. H. Daane, Eds. (Krieger, Huntington, N.Y., 1971, reprint of 1961 ed.) 641 pp; Hulet, Bode, "Separation Chemistry of the Lanthanides and Transplutonium Actinides" in MTP Int. Rev. Sci.: Inorg. Chem., Ser. One Vol. 7, K. W. Bagnall, Ed. (University Park Press, Baltimore, 1972) pp 1-45; Vickery, "Scandium, Yttrium, Lanthanum" in Comprehensive Inorganic Chemistry vol. 3, J. C. Bailar Jr. et al., Eds. (Pergamon Press, Oxford, 1973) pp 329-353; Moeller, "The Lanthanides" ibid. vol. 4, 1-101; F. H. Spedding in Kirk-Othmer Encyclopedia of Chemical Technology vol. 19 (John Wiley & Sons, New York, 3rd ed., 1982) pp 833-854; Chemistry of the Elements N. N. Greenwood, A. Earnshaw, Eds. (Pergamon Press, New York, 1984) pp 1102-1110, 1423-1449. Brief review of properties: G. T. Seaborg, Radiochim. Acta 61, 115-122 (1993).
Properties: White, malleable metal; tarnishes in air. Three crystalline forms: hexagonal a-form, d 6.162, transforms to b-form at 310°; face-centered cubic b-form, d 6.19, transforms to g-form at 864°; body-centered cubic g-form, d 5.97, exists at >864°. mp 920°. bp 3464°. Heat of fusion: 6.201 kJ/mol. Heat of sublimation (25°): 431.0 kJ/mol. E°(aq) La3+/La -2.52 V (calc). Very active; dec water slowly in the cold, more readily on heating. Readily attacked by mineral acids; not attacked by cold concd H2SO4. Burns in air at about 450° producing a mixture of oxide and nitride; forms the hydride on heating in hydrogen. Forms alloys with several metals.
Melting point: mp 920°
Boiling point: bp 3464°
Density: d 6.162; d 6.19; d 5.97
Derivative Type: Oxide
Additional Names: Lanthana; lanthanum sesquioxide; lanthanum trioxide
Molecular Formula: La2O3
Molecular Weight: 325.81
Percent Composition: La 85.27%, O 14.73%
Properties: Almost white, amorphous powder. d 6.51. mp >2000°. Insol in water. Sol in dil mineral acids with formation of salts. Absorbs CO2 from the air.
Melting point: mp >2000°
Density: d 6.51
Derivative Type: Hydroxide
Molecular Formula: La(OH)3
Molecular Weight: 189.93
Percent Composition: La 73.14%, O 25.27%, H 1.59%
Properties: White, amorphous precip, prepd by adding excess of caustic alkali to a lanthanum salt soln. Strongly basic, displaces ammonia from ammonium salts, absorbs CO2 from air. On dehydration yields La2O3.H2O.
Derivative Type: Chloride
Molecular Formula: LaCl3
Molecular Weight: 245.26
Percent Composition: La 56.64%, Cl 43.37%
Properties: Heptahydrate, triclinic crystals. Sol in water or alc. On heating in HCl the anhydr salt (mp 852°) is formed. LD50 in rats: 4.2 g/kg orally; 350 mg/kg i.p. (Cochran).
Melting point: mp 852°
Toxicity data: LD50 in rats: 4.2 g/kg orally; 350 mg/kg i.p. (Cochran)
Derivative Type: Carbonate octahydrate
Additional Names: Artificial lanthanite
Molecular Formula: C3La2O9
Molecular Weight: 457.84
Percent Composition: C 7.87%, La 60.68%, O 31.45%
Properties: White, crystalline powder. Practically insol in water. Freely sol in dil mineral acids.
Derivative Type: Sulfate
Molecular Formula: La2(SO4)3
Molecular Weight: 566.00
Percent Composition: La 49.08%, S 17.00%, O 33.92%
Properties: Nonahydrate, hexagonal prisms. Prepd by treating a lanthanum salt with a slight excess of sulfuric acid. Dec at white heat. Is the least sol of the rare earth sulfates; soly in water decreases with increase in temp. Insol in alc. Forms double salts with alkali or ammonium hydroxide. Anhydr salt prepd by heating hydrate. LD50 in rats: >5000 g/kg orally; 275 mg/kg i.p. (Cochran).
Toxicity data: LD50 in rats: >5000 g/kg orally; 275 mg/kg i.p. (Cochran)
Derivative Type: Nitrate
Molecular Formula: La(NO3)3
Molecular Weight: 324.92
Percent Composition: La 42.75%, N 12.93%, O 44.32%
Properties: Hexahydrate, white deliquesc crystals, mp ~40°, at higher temp forms a basic salt. bp 126°. Very sol in water, alc. Forms double salts with bivalent ion nitrates and ammonium nitrates. Keep well closed. LD50 in rats: 4.5 g/kg orally; 450 mg/kg i.p. (Cochran).
Melting point: mp ~40°
Boiling point: bp 126°
Toxicity data: LD50 in rats: 4.5 g/kg orally; 450 mg/kg i.p. (Cochran)
Use: Oxide in glass to improve optical properties. La3+ used in experimental biology as a specific antagonist of calcium: Weiss, Annu. Rev. Pharmacol. 14, 343 (1974).

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