Gallium(III) selenate
| Names | |
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| Other names
Gallium selenate | |
| Identifiers | |
PubChem CID |
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CompTox Dashboard (EPA) |
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| Properties | |
| Ga2(SeO4)3 | |
| Molar mass | 568.33 g/mol |
| Appearance | Colorless crystalline solid (hydrates) |
| Melting point | 550 °C (1,022 °F; 823 K) decomposes |
| Soluble in water | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Gallium(III) selenate is an inorganic compound of gallium and the selenate ion, with the chemical formula Ga2(SeO4)3. Several hydrated forms have been reported.
Preparation
[edit]Gallium(III) selenate can be prepared by reaction of gallium(III) hydroxide with selenic acid:[1]
- 2 Ga(OH)3 + 3 H2SeO4 → Ga2(SeO4)3 + 6 H2O
An early preparation used a slight deficiency of selenic acid and excess gallium hydroxide. After digestion near the boiling point, excess hydroxide was filtered off and the solution was evaporated at room temperature to give hydrated gallium selenate crystals.[2]
Properties
[edit]Gallium(III) selenate is readily soluble in water. Early measurements on hydrated material at 25 °C found approximately one part of the salt to dissolve in 1.74 parts of water.[2]
Several hydration states have been reported. Dennis and Bridgman obtained air-dried crystals corresponding approximately to Ga2(SeO4)3·16H2O, while freshly isolated crystals appeared to contain about 22 molecules of water per formula unit.[2] A later thermochemical study reported an octadecahydrate, Ga2(SeO4)3·18H2O.[3]
An acidic selenate, GaH(SeO4)2·10H2O, has also been reported when gallium selenate is crystallized in the presence of excess selenic acid.[1]
Structure
[edit]Anhydrous Ga2(SeO4)3 is isostructural with the corresponding anhydrous aluminium selenate and with related trivalent-metal sulfates.[4]
The structure is constructed from GaO6 coordination polyhedra and SeO4 tetrahedra linked through shared oxygen atoms.[4]
Thermal decomposition
[edit]Hydrated gallium selenates lose water progressively on heating. The acidic selenate is converted to the normal selenate at approximately 300 °C.[1]
Anhydrous Ga2(SeO4)3 decomposes at about 550 °C, ultimately yielding gallium(III) oxide and volatile selenium oxides.[1]
Double salts
[edit]Gallium(III) selenate forms double salts with alkali-metal selenates. The caesium compound CsGa(SeO4)2·12H2O is an alum-type salt and crystallizes in the characteristic octahedral habit of alums.[2]
Sodium and potassium gallium selenate double salts have also been reported.[1]
References
[edit]- 1 2 3 4 5 Zhang, Qinglian (ed.). 无机化学丛书 第二卷：铍 碱土金属 硼 铝 镓分族 [Inorganic Chemistry Series, Volume 2: Beryllium, Alkaline-Earth Metals, Boron, Aluminium and Gallium Groups] (in Chinese). Science Press. p. 574.
- 1 2 3 4 Dennis, L. M.; Bridgman, J. Allington (1919). "A Study of Certain Salts of Gallium". Journal of the American Chemical Society. 41.
- ↑ Chemical Thermodynamics of Selenium. Chemical Thermodynamics. Vol. 7. OECD Nuclear Energy Agency. 2005.
- 1 2 Perret, René; Rosso, Bernard. "Crystalline parameters of anhydrous trivalent sulfates and selenates. II. Aluminum and gallium selenates." Bulletin de la Société Chimique de France. 1968. 7: 2700–2701.