Caesium chromate
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| Names | |
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| IUPAC name
Caesium chromate
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| Other names
Dicaesium chromate
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| Identifiers | |
3D model (JSmol)
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| ChemSpider | |
| ECHA InfoCard | 100.033.296 |
| EC Number |
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PubChemCID
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CompTox Dashboard(EPA)
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| Properties[1] | |
| Cs2CrO4 | |
| Appearance | Yellow crystalline solid |
| Density | 4.237 g/cm3 |
| Melting point | 954 to 961 °C (1,749 to 1,762 °F; 1,227 to 1,234 K) |
| 45.50 g/100 g (25 °C) | |
| Structure | |
| orthorhombic | |
| Pnma (№ 62) | |
a= 8.368 Å,b= 6.226 Å,c= 11.135 Å
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| 4 | |
| Hazards | |
| Occupational safety and health(OHS/OSH): | |
Main hazards
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highly toxic, carcinogenic, oxidiser, environmental hazard |
| GHSlabelling: | |
   
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| Flash point | Non-flammable |
| Related compounds | |
Otheranions
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Caesium sulfate |
Othercations
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Sodium chromate Potassium chromate Ammonium chromate |
Except where otherwise noted, data are given for materials in theirstandard state(at 25 °C [77 °F], 100 kPa).
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Caesium chromateorcesium chromateis an inorganic compound with the formula Cs2CrO4.It is a yellow crystalline solid that is thecaesiumsaltofchromic acid,and it crystallises in theorthorhombicsystem.
Its major application in the past was for the production of caesium vapour duringvacuum tubemanufacture.[2]Currently it is only used as the precursor for other compounds of academic interest.[3][4]
Preparation
[edit]Caesium chromate is mainly obtained from the reaction ofchromium(VI) oxidewithcaesium carbonate,whereincarbon dioxidegas is evolved:[3]
- CrO3(aq) + Cs2CO3(aq) → Cs2CrO4(aq) + CO2(g)
Alternatively,salt metathesisbetweenpotassium chromateandcaesium chloridecan be performed:[4]
- K2CrO4(aq) + 2 CsCl(aq) → Cs2CrO4(aq) + 2 KCl(aq)
Finally,caesium dichromate(itself derivedviasalt metathesis fromammonium dichromate) yields the chromate following alkalinisation withcaesium hydroxide:[2]
- Cs2Cr2O7(aq) + 2 CsOH(aq) → 2 Cs2CrO4(aq) + H2O(ℓ)
Applications
[edit]Caesium chromate was formerly used in the final stages of creating vacuum tubes. Therein, caesium vapour was produced by reaction of caesium chromate withsilicon,boron,ortitaniumas reducing agents. The vapour was then added to the tube to react with and remove remaining gases, includingnitrogenandoxygen.[5]
References
[edit]- ^Weast, Robert C., ed. (1981).CRC Handbook of Chemistry and Physics(62nd ed.). Boca Raton, FL: CRC Press. p. B-91.ISBN0-8493-0462-8..
- ^abLiebhafsky, H. A.; Winslow, A. F. (1947), "Cesium Chromate Photo-Tube Pellets",Journal of Applied Physics,18(12), Journal of Applied Physics, Vol. 18, No. 12: 1128,Bibcode:1947JAP....18.1128L,doi:10.1063/1.1697594
- ^abPejov, Ljupčo; Petruševski, Vladimir M (2003-08-01)."Latent symmetry versus accidental degeneracy effects in the vibrational spectra of dopant chromate anions in M2CrxS1−xO4 solid solutions (M∈{K, Rb, Cs})".Journal of Physics and Chemistry of Solids.64(8): 1353–1363.doi:10.1016/S0022-3697(03)00160-4.ISSN0022-3697.
- ^abBender, Johannes; Wohlfarth, Andreas; Hoch, Constantin (2010-12-01)."Crystal Structures of New Alkali Metal-rich Oxometallates: Rubidium Aluminate Tetrahydroxide, Rb9(AlO4)(OH)4, Rubidium Orthogallate, Rb5GaO4, Cesiumbis-Chromate(IV) Oxide, Cs10(CrO4)2O, and Cesium Diindate, Cs8In2O7".Zeitschrift für Naturforschung B.65(12): 1416–1426.doi:10.1515/znb-2010-1202.ISSN1865-7117.S2CID12985977.
- ^Emsley, John (2001),Nature's Building Blocks: An A-Z Guide to the Elements,Oxford University Press, p. 81,ISBN0-19-850340-7.