Potassium chromate
Names
IUPAC name
Potassium chromate
Other names
Chromic acid, (K2CrO4), dipotassium salt
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.029.218 Edit this at Wikidata
EC Number
  • 232-140-5
RTECS number
  • GB2940000
UNII
  • InChI=1S/Cr.2K.4O/q;2*+1;;;2*-1 ☒N
    Key: XMXNVYPJWBTAHN-UHFFFAOYSA-N ☒N
  • InChI=K2CrO4
    Key: XMXNVYPJWBTAHN-QALQIXLOAU
  • [O-][Cr](=O)(=O)[O-].[K+].[K+]
Properties
K
2CrO
4
Molar mass 194.189 g·mol−1
Appearance Yellow powder
Odor odorless
Density 2.7320 g/cm3
Melting point 968 °C (1,774 °F; 1,241 K)
Boiling point 1,000 °C (1,830 °F; 1,270 K)
62.9 g/100 mL (20 °C)

75.1 g/100 mL (80 °C)
79.2 g/100 mL (100 °C)
Solubility insoluble in alcohol
−3.9·10−6 cm3/mol
1.74
Structure
rhombic
Hazards
GHS labelling:
H315, H317, H319, H335, H340, H350i, H410
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 0: Will not burn. E.g. waterInstability 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g. calciumSpecial hazard OX: Oxidizer. E.g. potassium perchlorate
3
0
1
OX
Safety data sheet (SDS) Chemical Safety Data
Related compounds
Other anions
 Potassium dichromate
Potassium molybdate
Potassium tungstate
Other cations
 Sodium chromate
Calcium chromate
Barium chromate
Related chromates
 Potassium hypochromate
Potassium perchromate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Potassium chromate is the inorganic compound with the formula K2CrO4. This yellow solid is the potassium salt of the chromate anion. It is a common laboratory chemical, whereas sodium chromate is important industrially.

Structure

Two crystalline forms are known, both being very similar to the corresponding potassium sulfate. Orthorhombic β-K2CrO4 is the common form, but it converts to an α-form above 66 °C.[1] These structures are complex, although the chromate ion adopts the typical tetrahedral geometry.[2]

Production and reactions

It is prepared by treating potassium dichromate with potassium hydroxide:

Or, the fusion of potassium hydroxide and chromium trioxide:

In solution, the behavior of potassium and sodium dichromates are very similar. When treated with lead(II) nitrate, it gives an orange-yellow precipitate, lead(II) chromate.

Applications

Unlike the less expensive sodium salt, potassium salt is mainly used for laboratory work in situations where an anhydrous salt is required.[1] It is as an oxidizing agent in organic synthesis. It is used in qualitative inorganic analysis, e.g. as a colorimetric test for silver ion. It is also used as an indicator in precipitation titrations with silver nitrate and sodium chloride (they can be used as standard as well as titrant for each other) as potassium chromate turns red in the presence of excess of silver ions.

Occurrence

Tarapacaite is the natural, mineral form of potassium chromate. It occurs very rarely and until now is known from only few localities on Atacama Desert.[citation needed]

Safety

As with other Cr(VI) compounds, potassium chromate is carcinogenic.[3] The compound is also corrosive and exposure may produce severe eye damage or blindness.[4] Human exposure further encompasses impaired fertility, heritable genetic damage and harm to unborn children.

References

  1. ^ a b Gerd Anger, Jost Halstenberg, Klaus Hochgeschwender, Christoph Scherhag, Ulrich Korallus, Herbert Knopf, Peter Schmidt, Manfred Ohlinger, "Chromium Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005. doi:10.1002/14356007.a07_067
  2. ^ Gaultier, M.; Pannetier, G. "Structure cristalline de la forme 'basse temperature' du sulfate de potassium K2SO4-beta" (Crystal structure of the "low temperature" β-form of potassium sulfate) Bulletin de la Société Chimique de France 1968, vol. 1, pp. 105-12.
  3. ^ IARC (2012) [17–24 March 2009]. Volume 100C: Arsenic, Metals, Fibres, and Dusts (PDF). Lyon: International Agency for Research on Cancer. ISBN 978-92-832-0135-9. Retrieved 2020-01-05. There is sufficient evidence in humans for the carcinogenicity of chromium (VI) compounds. Chromium (VI) compounds cause cancer of the lung. Also positive associations have been observed between exposure to Chromium (VI) compounds and cancer of the nose and nasal sinuses. There is sufficient evidence in experimental animals for the carcinogenicity of chromium (VI) compounds. Chromium (VI) compounds are carcinogenic to humans (Group 1).
  4. ^ "Potassium dichromate MSDS". JT Baker.
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