Potassium chromate

Potassium chromate

Names
IUPAC name Potassium chromate
Other names Chromic acid, (K2CrO4), dipotassium salt
Identifiers
CAS Number	7789-00-6 Y
3D model (Jmol)	Interactive image
ChEBI	CHEBI:75249 N
ChemSpider	22999 N
ECHA InfoCard	100.029.218
EC Number	232-140-5
PubChem	24597
RTECS number	GB2940000
InChI InChI=1S/Cr.2K.4O/q;2*+1;;;2*-1 N Key: XMXNVYPJWBTAHN-UHFFFAOYSA-N N InChI=1/Cr.2K.4O/q;2*+1;;;2*-1/rCrO4.2K/c2-1(3,4)5;;/q-2;2*+1 Key: XMXNVYPJWBTAHN-QALQIXLOAU
SMILES [O-][Cr](=O)(=O)[O-].[K+].[K+]
Properties
Chemical formula	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)
Solubility in water	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
Refractive index (nD)	1.74
Structure
Crystal structure	rhombic
Hazards
Safety data sheet	Chemical Safety Data
EU classification (DSD)	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	0 3 1 OX
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 YN ?)
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

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]

• 
  Structure of β-K₂CrO₄.
• 
  Coordination sphere of one of two types of K⁺ site.
• 
  The environment about the tetrahedral CrO₄^2- center in β-K₂CrO₄.

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.