Aluminium arsenate

Aluminium arsenate is an inorganic compound with the formula AlAsO₄.^[2] It is most commonly found as an octahydrate. It is a colourless solid that is produced by the reaction between sodium arsenate and a soluble aluminium salt. Aluminium arsenate occurs naturally as the mineral mansfieldite.^[3] Anhydrous form is known as an extremely rare, fumarolic mineral alarsite^[4] A synthetic hydrate of aluminium arsenate is produced by hydrothermal method. with the formulation Al₂O₃·3As₂O₅·10H₂O.^[5]

Aluminium arsenate

Names
Other names Aluminium arsenate
Identifiers
CAS Number	13462-91-4 Y (Octahydrate): 60763-04-4 Y
3D model (JSmol)	Interactive image (Octahydrate): Interactive image
ChemSpider	10636688 (Octahydrate): 21391673
PubChem CID	57351442 (Octahydrate): 24884165
CompTox Dashboard (EPA)	DTXSID601031713 (Octahydrate): DTXSID70647789
InChI InChI=1S/Al.AsH3O4/c;2-1(3,4)5/h;(H3,2,3,4,5)/q+3;/p-3 Key: RCJAOTMBSRLOJZ-UHFFFAOYSA-K (Octahydrate): InChI=1S/Al.AsH3O4.8H2O/c;2-1(3,4)5;;;;;;;;/h;(H3,2,3,4,5);8*1H2/q+3;;;;;;;;;/p-3 Key: CHNKHEXWDMIYLG-UHFFFAOYSA-K
SMILES [O-][As](=O)([O-])[O-].[Al+3] (Octahydrate): O.O.O.O.O.O.O.O.O=[As]([O-])([O-])[O-].[Al+3]
Properties
Chemical formula	AlAsO4
Molar mass	165.899 g·mol−1
Appearance	colourless crystals
Density	3.25 g/cm3
Melting point	1,000 °C (1,830 °F; 1,270 K)
Solubility in water	insoluble
Solubility product (Ksp)	10−18.06 for 2 AlAsO4.7 H2O.[1]
Refractive index (nD)	1.596
Structure
Crystal structure	hexagonal
Thermochemistry
Std molar entropy (S⦵298)	145.6 J/mol K
Std enthalpy of formation (ΔfH⦵298)	−1431.1 kJ/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Modification of aluminium orthoarsenate was carried out by heating different samples to different temperatures. Both amorphous and crystalline forms were obtained.^[6] The solubility product was determined to be 10^−18.06 for aluminium arsenate hydrate of formula AlAsO₄·3.5H₂O.^[1] Like gallium arsenate and boron arsenate, it adopts the α-quartz-type structure. The high pressure form has a rutile-type structure in which aluminium and arsenic are six-coordinate.