Calcium arsenate
| Calcium arsenate | |
|---|---|
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Other names
Calcium orthoarsenate |
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| Identifiers | |
| CAS number | 7778-44-1  = |
| PubChem | 24501 |
| KEGG | C18647 |
| RTECS number | CG0830000 |
| Properties | |
| Molecular formula | Ca3As2O8 |
| Molar mass | 398.072 g/mol |
| Appearance | white powder |
| Odor | odorless |
| Density | 3.62 g/cm3, solid |
| Melting point |
1455°C (decomposes) |
| Solubility in water | 0.013 g/100 mL (25 °C)[1] |
| Solubility in Organic solvents | insoluble |
| Solubility in acids | soluble |
| Hazards | |
| LD50 | 20 mg/kg (rat, oral) |
 (verify) (what is:  / ?)Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
Calcium arsenate is the inorganic compound with the formula Ca3(AsO4)2. A colourless solid, it was originally used as a pesticide and as a germicide. It is highly soluble in water, as compared with lead arsenate, which makes it more toxic.
Contents |
Preparation[edit]
Calcium arsenate is commonly prepared by 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.[2] In the United States, 1360 metric tons were produced in 1919, 4540 in 1920, and 7270 in 1922.[1]
Use as an herbicide[edit]
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.[3]
Regulation[edit]
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.[4]
Toxicity and regulation[edit]
Calcium arsenate is highly toxic, having both carcinogenic and systemic health effects.[5]
References[edit]
- ^ a b Tartar, H.V.; Wood, L; Hiner, E; A Basic Arsenate of Calcium. J. Am. Chem. Soc. 1924, vol. 46, 809-813.
- ^ Smith, C.M.; Murray, C.W.; The Composition of Commercial Calcium Arsenate. Journal of Industrial and Engineering Chemistry; 1931, 23
- ^ Robert L. Metcalf “Insect Control” in Ullmann’s Encyclopedia of Industrial Chemistry” Wiley-VCH, Weinheim, 2002. doi:10.1002/14356007.a14_263
- ^ Turf insect pest control guide: Urban Phytonarian Series. learningstore.uwex.edu/pdf/A2934.pdf (Accessed 04/16/10)
- ^ 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
