Nomenclature
CAS number: 7439-91-0
Description and 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, T 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 α-form, d 6.162, transforms to β-form at 310°; face-centered
cubic β-form, d 6.19, transforms to γ-form at 864°; body-centered cubic γ-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.Derivative
Oxide.
Nomenclature
CAS number: 1312-81-8
Lanthanum oxide (La
2O
3); lanthana; lanthanum sesquioxide; lanthanum trioxide.
La
2O
3; mol wt 325.81.
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.Derivative
Hydroxide.
Nomenclature
CAS number: 14507-19-8
Lanthanum hydroxide (La(OH)
3).
H
3LaO
3; mol wt 189.93.
H 1.59%, La 73.14%, O 25.27%.
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
Chloride.
Nomenclature
CAS number: 10099-58-8;
10025-84-0
(heptahydrate)
Lanthanum chloride (LaCl
3).
Cl
3La; mol wt 245.26.
Cl 43.37%, La 56.64%.
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).Derivative
Sulfate.
Nomenclature
CAS number: 10099-60-2;
10294-62-9
(nonahydrate)
Sulfuric acid lanthanum(3+) salt (3:2).
La
2O
12S
3; mol wt 566.00.
La 49.08%, O 33.92%, S 17.00%.
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: >5.0 g/kg orally; 275 mg/kg i.p. (Cochran).Derivative
Nitrate.
Nomenclature
CAS number: 10099-59-9;
10277-43-7
(hexahydrate)
Nitric acid lanthanum(3+) salt (3:1).
LaN
3O
9; mol wt 324.92.
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).Use
Oxide in glass to improve optical properties. Chloride
heptahydrate as matrix modifier in analytical chemistry. La
3+ used in experimental biology as a specific antagonist of calcium:
Weiss,
Annu. Rev. Pharmacol. 14, 343 (1974).