Potassium chromate

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Not to be confused with Potassium dichromate.
Potassium chromate
Potassium-chromate-sample.jpg
Potassium chromate.svg
Names
IUPAC name
Potassium chromate
Other names
Chromic acid, (K2CrO4), dipotassium salt
Identifiers
3D model (Jmol)
ChEBI
ChemSpider
ECHA InfoCard 100.029.218
EC Number 232-140-5
RTECS number GB2940000
Properties
CrK2O4
Molar mass 194.19 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
Safety data sheet Chemical Safety Data
Carc. Cat. 2
Muta. Cat. 2
Toxic (T)
Irritant (Xi)
Dangerous for the environment (N)
R-phrases R49, R46, R36/37/38, R43, R50/53
S-phrases S53, S45, S60, S61
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calcium Special hazard OX: Oxidizer. E.g., potassium perchlorateNFPA 704 four-colored diamond
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).
N verify (what is YesYN ?)
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.[1]

Structure[edit]

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[edit]

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[edit]

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[edit]

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[edit]

Potassium chromate is a carcinogen and strong oxidant.

References[edit]

  1. ^ Potassium chromate information URL last accessed 15 March 2007
  2. ^ 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
  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.