Calcium arsenate
{{Use dmy dates|date=February 2023}}
{{chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 440601674
| Name = Calcium arsenate
| ImageFile = Calciumarsenaat.png
| ImageSize =
|IUPACName=Calcium arsorate
| ImageName = Calcium arsenate
| ImageFile2 = Arsenian Wapnia.jpg
| ImageSize2 =
| ImageName2 = Calcium arsenate
| OtherNames = Calcium orthoarsenate
Cucumber dust
Tricalcium arsenate
Tricalcium ortho-arsenate
|Section1={{Chembox Identifiers
| CASNo = 7778-44-1
| CASNo_Ref = {{cascite|correct|??}}
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 95OX15I8ZU
| PubChem = 24501
| RTECS = CG0830000
| KEGG_Ref = {{keggcite|correct|kegg}}
| KEGG = C18647
| EINECS = 233-287-8
| ChemSpiderID_Ref = {{chemspidercite|changed|chemspider}}
| ChemSpiderID = 22909
| SMILES = [O-][As](=O)([O-])[O-].[O-][As](=O)([O-])[O-].[Ca+2].[Ca+2].[Ca+2]
| InChI = 1/2AsH3O4.3Ca/c2*2-1(3,4)5;;;/h2*(H3,2,3,4,5);;;/q;;3*+2/p-6
| InChIKey = RMBBSOLAGVEUSI-CYFPFDDLAC
| StdInChI_Ref = {{stdinchicite|changed|chemspider}}
| StdInChI = 1S/2AsH3O4.3Ca/c2*2-1(3,4)5;;;/h2*(H3,2,3,4,5);;;/q;;3*+2/p-6
| StdInChIKey_Ref = {{stdinchicite|changed|chemspider}}
| StdInChIKey = RMBBSOLAGVEUSI-UHFFFAOYSA-H
}}
|Section2={{Chembox Properties
| Formula = Ca3(AsO4)2
| MolarMass = 398.072 g/mol
| Appearance = white powder
| Odor = odorless
| Density = 3.62 g/cm3, solid
| Solubility = 0.013 g/100 mL (25 °C)Tartar, H.V.; Wood, L; Hiner, E; A Basic Arsenate of Calcium. J. Am. Chem. Soc. 1924, vol. 46, 809-813.
| Solvent1 = Organic solvents
| Solubility1 = insoluble
| Solvent2 = acids
| Solubility2 = soluble
| MeltingPtC = 1455
| MeltingPt_notes = (decomposes)
| BoilingPt =
}}
|Section3={{Chembox Hazards
| NFPA-H = 4
| NFPA-R = 0
| NFPA-F = 0
| NFPA-S =
| LD50 = 20 mg/kg (rat, oral)
82 mg/kg (rat, oral)
74 mg/kg (mouse, oral)
50 mg/kg (rabbit, oral)
38 mg/kg (dog, oral){{IDLH|7778441|Calcium arsenate (as As)}}
| PEL = TWA 0.010 mg/m3{{PGCH|0089}}
| REL = Ca C 0.002 mg/m3 [15-minute]
| MainHazards = carcinogen
| FlashPt = noncombustible
}}
}}
Calcium arsenate is the inorganic compound with the formula Ca3(AsO4)2. A colourless salt, it was originally used as a pesticide and as a germicide. It is highly soluble in water, in contrast to lead arsenate, which makes it more toxic. Two minerals are hydrates of calcium arsenate: rauenthalite Ca3(AsO4)2·10H2O and phaunouxite Ca3(AsO4)2·11H2O.{{cite journal |doi=10.3406/bulmi.1982.7624 |title=Phaunouxite Ca3(AsO4)2•11H2O, a New Mineral Strictly Associated with Rauenthalite |date=1982 |last1=Bari |first1=Hubert |last2=Catti |first2=Michele |last3=Ferraris |first3=Giovanni |last4=Ivaldi |first4=Gabriella |last5=Permingeat |first5=François |journal=Bulletin de Minéralogie |volume=105 |issue=4 |pages=327–332 }} A related mineral is ferrarisite ({{chem2|Ca5H2(AsO4)4*9H2O}}.{{cite journal |doi=10.3406/bulmi.1980.7417 |title=La ferrarisite Ca5H2(AsO4)4.9 H2O, une Nouvelle Espèce Minérale Dimorphe de la Guérinite |date=1980 |last1=Bari |first1=Hubert |last2=Permingeat |first2=François |last3=Pierrot |first3=Roland |last4=Walenta |first4=Kurt |journal=Bulletin de Minéralogie |volume=103 |issue=5 |pages=533–540 }}
Preparation
Calcium arsenate is commonly prepared from disodium hydrogen arsenate and calcium chloride:
:2 Na2H[AsO4] + 3 CaCl2 → 4 NaCl + Ca3[AsO4]2 + 2 HCl
In the 1920s, it was made in large vats by mixing calcium oxide and arsenic oxide.Smith, C.M.; Murray, C.W.; The Composition of Commercial Calcium Arsenate. Journal of Industrial and Engineering Chemistry; 1931, 23 In the United States, 1360 metric tons were produced in 1919, 4540 in 1920, and 7270 in 1922.
The composition of commercially available calcium arsenate varies from manufacturer to manufacturer. A typical composition is 80-85% of Ca3(AsO4)2 a basic arsenate probably with a composition of 4CaO.As2O5 together with calcium hydroxide and calcium carbonate.{{cn|date=September 2023}}
Use as a herbicide
It was once a common herbicide and insecticide. 38,000,000 kilograms were reported to be produced in 1942 alone, mainly for protection of cotton crops. Its high toxicity led the development of DDT.Robert L. Metcalf "Insect Control" in Ullmann’s Encyclopedia of Industrial Chemistry Wiley-VCH, Weinheim, 2002. {{doi|10.1002/14356007.a14_263}}
=Regulation=
Calcium arsenate use is now banned in the UK, and its use is strictly regulated in the United States. It is currently the active ingredient in TURF-Cal manufactured by Mallinckrodt, it is one of the few herbicides – used mainly for the control of Poa annua and crabgrass- that hinders earthworm activity. Its label states that it will "reduce and inhibit earthworm activity and survival" and is only recommended against serious earthworm infestations in places such as golf course greens.{{cite web | title=Turf insect pest control guide: Urban Phytonarian Series | url=http://learningstore.uwex.edu/assets/pdfs/A2934.pdf | first=C.F. | last=Koval | publisher=College of Agricultural and Life Sciences – University of Wisconsin-Madison | access-date=9 November 2018 }}
Toxicity and regulation
Calcium arsenate is highly toxic, having both carcinogenic and systemic health effects.Tchounwou, P.B.; Patlolla, A.K.; Centeno, J.A.; Carcinogenic and Systematic Health Effects Associated with Arsenic – A Critical Review. Toxicologic Pathology; 2003, 31, 575-588 The Occupational Safety and Health Administration has set a permissible exposure limit at 0.01 mg/m3 over an eight-hour time-weighted average, while the National Institute for Occupational Safety and Health recommends a limit five times less (0.002 mg/m3).{{cite web| title = Calcium Arsenate| work = NIOSH Pocket Guide to Chemical Hazards| publisher = Centers for Disease Control and Prevention| date = 4 April 2011| url = https://www.cdc.gov/niosh/npg/npgd0089.html| access-date = 18 November 2013}}
It is classified as an extremely hazardous substance in the United States as defined in Section 302 of the U.S. Emergency Planning and Community Right-to-Know Act (42 U.S.C. 11002), and is subject to strict reporting requirements by facilities which produce, store, or use it in significant quantities.{{Cite journal | publisher = Government Printing Office | title = 40 C.F.R.: Appendix A to Part 355—The List of Extremely Hazardous Substances and Their Threshold Planning Quantities | url = http://edocket.access.gpo.gov/cfr_2008/julqtr/pdf/40cfr355AppA.pdf | edition = 1 July 2008 | access-date = 29 October 2011 | archive-url = https://web.archive.org/web/20120225051612/http://edocket.access.gpo.gov/cfr_2008/julqtr/pdf/40cfr355AppA.pdf | archive-date = 25 February 2012 | url-status = dead }}
Other natural occurrences
Weilite is the monohydrogenated counterpart, Ca(HAsO4),{{Cite web|url=https://www.mindat.org/min-4259.html|title=Weilite}} while švenekite – the dihydrogenated one, Ca(H2AsO4)2.{{Cite web|url=https://www.mindat.org/min-7076.html|title=Švenekite}} Hydrated analogues of weilite are haidingerite (monohydrate) and pharmacolite (dihydrate), with the latter name reflecting arsenic-related toxicity. Examples of more complex, hydrated Ca arsenates with some anions hydrogenated, are ferrarisite,{{Cite web|url=https://www.mindat.org/min-1485.html|title=Ferrarisite}} guérinite,{{Cite web|url=https://www.mindat.org/min-1767.html|title=Guérinite}} sainfeldite,{{Cite web|url=https://www.mindat.org/min-3503.html|title=Sainfeldite}} vladimirite,{{Cite web|url=https://www.mindat.org/min-4195.html|title=Vladimirite}} and jeankempite.{{Cite web|url=https://www.mindat.org/min-53206.html|title = Jeankempite}}{{Cite web|url=https://www.ima-mineralogy.org/Minlist.htm|title=List of Minerals|date=21 March 2011}}
References
{{Reflist}}
{{Calcium compounds}}
{{Insecticides}}
{{DEFAULTSORT:Calcium Arsenate}}