calcium chromate
{{chembox
| Watchedfields = changed
| verifiedrevid = 472231906
| Name = Calcium Chromate
| ImageFile = Calcium chromate formula.svg
| ImageSize =
| ImageCaption = Anhydrous calcium chromate
| ImageFile1 =Kalsiyum kromat.jpg
| ImageSize1 = 200 px
| ImageCaption1 = Calcium chromate pigment
| IUPACName = Calcium chromate
| OtherNames = Calcium chromate (VI)
Calcium monochromate
Calcium Chrome Yellow
C. I. Pigment Yellow 33
Gelbin
Yellow Ultramarine
|Section1={{Chembox Identifiers
| CASNo_Ref = {{cascite|correct|??}}
| CASNo = 13765-19-0
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = J1FGH4ZJ4M
| PubChem = 26264
| EINECS = 237-66-8
| RTECS = GB2750000
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 24471
| SMILES = [Ca+2].[O-][Cr]([O-])(=O)=O
| InChI = 1/Ca.Cr.4O/q+2;;;;2*-1/rCa.CrO4/c;2-1(3,4)5/q+2;-2
| InChIKey = RFAFBXGYHBOUMV-DETYUTSMAY
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/Ca.Cr.4O/q+2;;;;2*-1
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = RFAFBXGYHBOUMV-UHFFFAOYSA-N
}}
|Section2={{Chembox Properties
| Formula = CaCrO4
| MolarMass = 156.072 g/mol
| Appearance = bright yellow powder
| Density = 3.12 g/cm3
| Solubility = 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)
| SolubleOther = soluble in acid
practically insoluble in alcohol
| MeltingPtC = 2710
| MeltingPt_notes =
}}
|Section3={{Chembox Structure
| Coordination =
| CrystalStruct = monoclinic
}}
|Section8={{Chembox Related
| OtherAnions = Calcium dichromate
| OtherCations = Beryllium chromate
Magnesium chromate
Strontium chromate
Barium chromate
Radium chromate}}
|Section9={{Chembox Hazards
| MainHazards = highly toxic, carcinogen, mutagen
| NFPA-H = 3
| NFPA-F = 0
| NFPA-R = 1
| NFPA-S = OX
}}
}}
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.{{cite web |url=http://www.mindat.org/ |title=Home |website=mindat.org}}
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|date=March 2021}}
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.[http://www.osha.gov/SLTC/healthguidelines/calciumchromate/recognition.html Occupational Safety And Health Guideline For Calcium Chromate] {{webarchive |url=https://web.archive.org/web/20070808184626/http://www.osha.gov/SLTC/healthguidelines/calciumchromate/recognition.html |date=August 8, 2007 }}
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|date=March 2021}}
It has been also utilised in chromium electroplating, in photochemical processing, and as an industrial waste treatment.{{Citation needed|date=March 2021}}
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.{{cite book|author=IARC|url=https://publications.iarc.fr/_publications/media/download/3026/50ed50733f7d1152d91b30a803619022ef098d59.pdf|title=Volume 100C: Arsenic, Metals, Fibres, and Dusts|date=2012|publisher=International Agency for Research on Cancer|isbn=978-92-832-0135-9|location=Lyon|quote=There is sufficient evidence in humans for the carcinogenicity of chromium (VI) compounds. Chromium (VI) compounds cause cancer of the lung. Also positive associations have been observed between exposure to Chromium (VI) compounds and cancer of the nose and nasal sinuses. There is sufficient evidence in experimental animals for the carcinogenicity of chromium (VI) compounds. Chromium (VI) compounds are carcinogenic to humans (Group 1).|author-link=International Agency for Research on Cancer|access-date=2020-01-05|orig-year=17-24 March 2009|archive-date=2020-03-17|archive-url=https://web.archive.org/web/20200317095517/https://publications.iarc.fr/_publications/media/download/3026/50ed50733f7d1152d91b30a803619022ef098d59.pdf|url-status=dead}}{{Cite web|title=Calcium chromate 10827-V|url=https://ntp.niehs.nih.gov/whatwestudy/testpgm/status/ts-10827-v.html|access-date=2021-03-30|website=ntp.niehs.nih.gov|publisher=National Toxicology Program (United States Department of Health and Human Services)}}
References
{{reflist}}
{{Calcium compounds}}
{{Chromates and dichromates}}