Potassium chromate

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
EC Number 232-140-5
RTECS number GB2940000
Properties
K
2CrO
4
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
Safety data sheet Chemical Safety Data
NFPA 704
Related compounds
Other anions
 Potassium dichromate
Potassium molybdate
Potassium tungstate
Other cations
 Sodium chromate
Calcium chromate
Barium chromate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

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. It is a class two carcinogen as it contains hexavalent chromium.[1]

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.[2] These structures are complex, although the sulfate adopts the typical tetrahedral geometry.[3]

Production and reactions

It is prepared by treating potassium dichromate with potassium hydroxide.

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.[2] It is as an oxidizing agent in organic synthesis. It is used as 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.

Safety

Potassium chromate is a carcinogen and strong oxidant.

References

  1. ↑ Potassium chromate information URL last accessed 15 March 2007
  2. 1 2 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
  3. ↑ 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 Societe Chimique de France 1968, vol. 1, pp. 105-12.


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