Potassium chromate

Potassium chromate

Names
IUPAC name Potassium chromate
Other names Potassium dichromate, Chromic acid, (K2CrO4), dipotassium salt
Identifiers
CAS Number	7789-00-6 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:75249 N
ChemSpider	22999 N
EC Number	232-140-5
PubChem CID	24597
RTECS number	GB2940000
UNII	5P0R38CN2X Y
UN number	3077
InChI InChI=1S/Cr.2K.4O/q;2*+1;;;2*-1 N Key: XMXNVYPJWBTAHN-UHFFFAOYSA-N N InChI=K2CrO4 Key: XMXNVYPJWBTAHN-QALQIXLOAU
SMILES [O-][Cr](=O)(=O)[O-].[K+].[K+]
Properties
Chemical formula	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)
Solubility in water	63.7 g/100 mL (20 °C (68 °F; 293 K)) 75.1 g/100 mL (80 °C (176 °F; 353 K)) 79.2 g/100 mL (100 °C (212 °F; 373 K))
Magnetic susceptibility (χ)	3.9×10−6 cm3/mol
Refractive index (nD)	1.74
Structure
Crystal structure	rhombic
Hazards
Safety data sheet	Fisher Scientific[1]
GHS pictograms
GHS Signal word	Danger
GHS hazard statements	H315, H317, H319, H335, H340, H350, H410
GHS precautionary statements	P201, P202, P261, P264, P271, P272, P273, P280, P302+352, P304+340+312Script error: No such module "Preview warning".Category:GHS errors, P305+351+338, P308+313, P333+313, P337+313, P362, P391, P403+233, P405, P501
NFPA 704 (fire diamond)	[1] 0 2 0
Related compounds
Other anions	Potassium dichromate
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).
N verify (what is YN ?)
Infobox references

Potassium chromate is the inorganic compound with the formula K
2CrO
4. 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 prepared by treating potassium dichromate with potassium hydroxide:

K
2Cr
2O
7(aq) + 2 KOH → 2 K
2CrO
4 + H
2O

Or, the fusion of potassium hydroxide and chromium trioxide:

2 KOH + CrO
3 → K
2CrO
4 + H
2O

When treated with lead(II) nitrate, it gives an orange-yellow precipitate, lead(II) chromate.

Unlike the less expensive sodium salt, the potassium salt is mainly used for laboratory work in situations where an anhydrous salt is required, or as an oxidizing agent in organic synthesis.^[3]

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.^{[citation needed]}

Two crystalline forms are known, both being very similar to the corresponding potassium sulfate. Orthorhombic β-K
2CrO
4 is the common form, but it converts to an α-form above 666 °C (1,231 °F).^[3] These structures are complex, although the chromate ion adopts the typical tetrahedral geometry.^{[4][better source needed]}

• 
  Structure of β-K₂CrO₄
• 
  Coordination sphere of one of two types of K+
  site
• 
  The environment about the tetrahedral CrO2−
  4 center in β-K
  2CrO
  4

As with other Cr(VI) compounds, potassium chromate is carcinogenic. Positive associations with lung cancer at a very high rate, and nasal / sinus cancer at a 100x lower rate have been found using worker exposure data. In general, less soluble chromates are a larger chronic hazard as they can be encapsulated in the lung without being absorbed and excreted, giving more time for reactive intermediates to be produced. Animal data indicates a potential for impaired fertility, heritable genetic damage and harm to unborn children, along with other types of cancer via less common exposure routes.^[5]

As a highly soluble hexavalent chromium compound, potassium chromate is also acutely toxic, though it is poorly absorbed from the intestinal tract.^[5] The compound is also corrosive and exposure may produce severe eye damage or blindness.^[1]

Template:Chromates and dichromates

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