515. Ammonium Dichromate(VI)

Nomenclature

CAS number: 7789-09-5
Chromic acid (H2Cr2O7) ammonium salt (1:2); ammonium bichromate.
Cr2H8N2O7; mol wt 252.06.
Cr 41.26%, H 3.20%, N 11.11%, O 44.43%.
(NH4)2Cr2O7.

Description and references

Prepd from ammonium sulfate and sodium dichromate or by the interaction of ammonia gas and chromic acid in soln: W. H. Hartford, Ind. Eng. Chem. 41, 1993 (1949); Chromium Chemicals Vol. 52 (Mutual Chem. Div., Allied Chem.) p. 34-39. Review: ACS Monograph Series no. 132, entitled “Chromium,” vol. 1, M. J. Udy, Ed. (Reinhold, New York, 1956) passim. Laboratory information profile: J. A. Young, J. Chem. Educ. 82, 1617 (2005).

Properties

Combustible solid. Strong oxidizer. Swells dramatically; closed containers may rupture violently when heated. Bright orange-red monoclinic prisms. Odorless and non-hygroscopic. d425 2.155. Bulk density: 82 lbs/cu ft. Dec at about 180°. Decomposition becomes self-sustaining at about 225° with spectacular swelling and evolution of heat and nitrogen, leaving Cr2O3. Heat of soln 23.0 cal/g. Very sol in water. Soly in water (w/w): 15.16% (0°); 26.67% (20°); 36.99% (40°); 46.14% (60°); 54.20% (80°); 60.89% (100°). Acid reaction. A 1% soln has a pH of 3.95 and a 10% soln has a pH of 3.45.

Caution

Irritating to eyes, skin and respiratory sytem. May cause ulcers of the nasal passages and pulmonary edema.

Use

Source of pure nitrogen (especially in the laboratory); in pyrotechnics (Vesuvius fire); in lithography and photo engraving; in special mordant, catalysts, and porcelain finishes; intermediate in the manuf of pigments; of magnetic recording materials. Oxidimentric standard in analytical chemistry.