Calcium chromate

Calcium chromate is an inorganic compound with the formula CaCrO₄, i.e. the chromate salt of calcium. It is a bright yellow solid which is normally found in the dihydrate form CaCrO₄·2H₂O. A very rare anhydrous mineral form exists in nature, which is known as chromatite.^[1]

Calcium Chromate

Anhydrous calcium chromate
Calcium chromate pigment
Names
IUPAC name Calcium chromate
Other names Calcium chromate (VI) Calcium monochromate Calcium Chrome Yellow C. I. Pigment Yellow 33 Gelbin Yellow Ultramarine
Identifiers
CAS Number	13765-19-0 Y
3D model (JSmol)	Interactive image
ChemSpider	24471 Y
ECHA InfoCard	100.033.955
EC Number	237-66-8
PubChem CID	26264
RTECS number	GB2750000
UNII	J1FGH4ZJ4M Y
CompTox Dashboard (EPA)	DTXSID0024717
InChI InChI=1S/Ca.Cr.4O/q+2;;;;2*-1 Y Key: RFAFBXGYHBOUMV-UHFFFAOYSA-N Y InChI=1/Ca.Cr.4O/q+2;;;;2*-1/rCa.CrO4/c;2-1(3,4)5/q+2;-2 Key: RFAFBXGYHBOUMV-DETYUTSMAY
SMILES [Ca+2].[O-][Cr]([O-])(=O)=O
Properties
Chemical formula	CaCrO4
Molar mass	156.072 g/mol
Appearance	bright yellow powder
Density	3.12 g/cm3
Melting point	2,710 °C (4,910 °F; 2,980 K)
Solubility in water	anhydrous 4.5 g/100 mL (0 °C) 2.25 g/100 mL (20 °C) dihydrate 16.3 g/100mL (20 °C) 18.2 g/100mL (40 °C)
Solubility	soluble in acid practically insoluble in alcohol
Structure
Crystal structure	monoclinic
Related compounds
Other anions	Calcium dichromate
Other cations	Beryllium chromate Magnesium chromate Strontium chromate Barium chromate Radium chromate
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	highly toxic, carcinogen, mutagen
NFPA 704 (fire diamond)	3 0 1 OX
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

The compound is occasionally used as a pigment, but this usage is limited due to the very toxic and carcinogenic nature of hexavalent chromium compounds such as chromate salts.

Synthesis and reactions

Calcium chromate is formed from the salt metathesis reaction of sodium chromate and calcium chloride:

Na₂CrO₄ + CaCl₂ → CaCrO₄ + 2 NaCl

In aqueous solution the dihydrate is obtained, which loses water to afford the anhydrate at 200 °C.^{[citation needed]}

It is an oxidiser, oxidising organic compounds (e.g. alcohols) or reducing agents (e.g. metals) to the corresponding carbonyl compounds or metal oxides while the chromium(VI) centre in CaCrO₄ is reduced to chromium(III).

Solid calcium chromate will react explosively with hydrazine. It will also burn violently if mixed with boron and ignited, thereby posing a fire hazard.^[2]

Uses

The compound is occasionally used as a yellow inorganic pigment, or a corrosion inhibitor as part of the chromate conversion coating procedure.^{[citation needed]}

It has been also utilised in chromium electroplating, in photochemical processing, and as an industrial waste treatment.^{[citation needed]}

All applications suffer from the high toxicity of chromium(VI) species to humans, with chromates listed as IARC Group 1 carcinogens while also very corrosive (e.g. capable of producing permanent eye damage) and genotoxic.^[3][4]