Nomenclature
CAS number: 7778-50-9
Chromic acid (H
2Cr
2O
7) potassium
salt (1:2); potassium bichromate.
Cr
2K
2O
7; mol wt 294.18.
Cr 35.35%, K 26.58%, O 38.07%.
K
2Cr
2O
7.
Description and references
In the U.S.A. it is usually prepared by the
reaction of potassium chloride on sodium dichromate: Vetter in Kirk-Othmer Encyclopedia of Chemical Technology vol. 3 (Interscience, New York, 1949) p 951; Hartford,
Copson, ibid. vol. 5 (2nd ed., 1964) pp 484-488.
In Germany it is obtained from potassium chromate produced by roasting
the chrome ore with KOH. Ref: Müller, Glissmann in Ullmanns Encyklop"adie der technischen Chemie vol. 5 (Munich, 3rd ed., 1954) p 580.
Properties
Bright orange-red crystals. Not hygroscopic or
deliquescent (difference from sodium dichromate). Crystal habit:
prismatic. Crystal system: triclinic pinacoidal, transition to
monoclinic at 241.6°. d425 2.676. Bulk density: 100 lbs/cu ft. mp 398°. Dec at about
500°. Heat of fusion 29.8 cal/g. Heat of soln -62.5 cal/g. Specific
heat 0.186 at 16° -98°. Soluble in water. A satd aq soln contains
at 0°: 4.3%, at 20°: 11.7%, at 40°: 20.9%, at 60°: 31.3%, at 80°:
42.0%, at 100°: 50.2%. Acid reaction: A 1% aq soln has a pH of
4.04 and a 10% soln has a pH of 3.57.Caution
Corrosive poison if ingested. Industrial
contact may result in ulceration of hands, destruction of mucous membranes
and perforation of nasal septum.
See E. Browning,
Toxicity of Industrial Metals (Appleton-Century
Crofts, New York, 2nd ed., 1969) pp 119-131.
See also Chromium.
Use
In tanning leather, dyeing, painting, decorating
porcelain, printing, photolithography, pigment-prints, staining wood,
pyrotechnics, safety matches; for bleaching palm oil, wax, and sponges;
waterproofing fabrics; as oxidizer in the manuf of organic chemicals;
in electric batteries; as depolarizer for dry cells. As corrosion
inhibitor in preference to sodium dichromate where lower soly is advantageous.
Pharmaceutic aid (oxidizing agent). Redox reagent.
Therapeutic Category (Veterinary)
Caustic.