Caesium chromate
{{chembox
| ImageFile = Cesium chromate crystals.jpg
| ImageSize =
| ImageFile1 = File:Caesium chromate formula.svg
| IUPACName =Caesium chromate
| OtherNames = Dicaesium chromate
|Section1={{Chembox Identifiers
| SMILES = [Cs+].[Cs+].[O-][Cr]([O-])(=O)=O
| InChIKey = BROHICCPQMHYFY-UICSPCLAAP
| CASNo = 13454-78-9
| EINECS = 236-640-4
| ChemSpiderID = 55521
| PubChem = 61613
| InChI = 1/Cr.2Cs.4O/q;2*+1;;;2*-1/rCrO4.2Cs/c2-1(3,4)5;;/q-2;2*+1
| RTECS =
}}
|Section2={{Chembox Properties
| Properties_ref = {{RubberBible62nd|page=B-91}}.
| Formula = Cs2CrO4
| Appearance = Yellow crystalline solid
| Density = 4.237 g/cm3
| MeltingPtC = 954 to 961
| MeltingPt_notes =
| BoilingPt =
| BoilingPt_notes =
| Solubility = 45.50 g/100 g (25 °C)
| SolubleOther =
| Solvent =
}}
| Section3 = {{Chembox Structure
| CrystalStruct = orthorhombic
| SpaceGroup = Pnma (№ 62)
| LattConst_a = 8.368 Å
| LattConst_b = 6.226 Å
| LattConst_c = 11.135 Å
| UnitCellFormulas = 4
}}
|Section7={{Chembox Hazards
| MainHazards = highly toxic, carcinogenic, oxidiser, environmental hazard
| GHSPictograms = {{GHS03}}{{GHS07}}{{GHS08}}{{GHS09}}
| FlashPt = Non-flammable
| PEL =
}}
|Section8={{Chembox Related
| OtherAnions = Caesium sulfate
| OtherCations = Sodium chromate
Potassium chromate
Ammonium chromate
| OtherFunction =
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| OtherCompounds =
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}}
Caesium chromate or cesium chromate is an inorganic compound with the formula Cs2CrO4. It is a yellow crystalline solid that is the caesium salt of chromic acid, and it crystallises in the orthorhombic system.
Its major application in the past was for the production of caesium vapour during vacuum tube manufacture.{{citation | title = Cesium Chromate Photo-Tube Pellets | first1 = H. A. | last1 = Liebhafsky | year = 1947 | publisher = Journal of Applied Physics, Vol. 18, No. 12 | page = 1128 | doi = 10.1063/1.1697594 | bibcode = 1947JAP....18.1128L | last2 = Winslow | first2 = A. F. | journal = Journal of Applied Physics | volume = 18 | issue = 12}} Currently it is only used as the precursor for other compounds of academic interest.{{Cite journal|last1=Pejov|first1=Ljupčo|last2=Petruševski|first2=Vladimir M|date=2003-08-01|title=Latent symmetry versus accidental degeneracy effects in the vibrational spectra of dopant chromate anions in M2CrxS1−xO4 solid solutions (M∈{K, Rb, Cs})|url=https://www.sciencedirect.com/science/article/pii/S0022369703001604|journal=Journal of Physics and Chemistry of Solids|language=en|volume=64|issue=8|pages=1353–1363|doi=10.1016/S0022-3697(03)00160-4|issn=0022-3697|url-access=subscription}}{{Cite journal|last1=Bender|first1=Johannes|last2=Wohlfarth|first2=Andreas|last3=Hoch|first3=Constantin|date=2010-12-01|title=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|journal=Zeitschrift für Naturforschung B|language=en|volume=65|issue=12|pages=1416–1426|doi=10.1515/znb-2010-1202|s2cid=12985977|issn=1865-7117|doi-access=free}}
Preparation
Caesium chromate is mainly obtained from the reaction of chromium(VI) oxide with caesium carbonate, wherein carbon dioxide gas is evolved:
: CrO3(aq) + Cs2CO3(aq) → Cs2CrO4(aq) + CO2(g)
Alternatively, salt metathesis between potassium chromate and caesium chloride can be performed:
: K2CrO4(aq) + 2 CsCl(aq) → Cs2CrO4(aq) + 2 KCl(aq)
Finally, caesium dichromate (itself derived via salt metathesis from ammonium dichromate) yields the chromate following alkalinisation with caesium hydroxide:
: Cs2Cr2O7(aq) + 2 CsOH(aq) → 2 Cs2CrO4(aq) + H2O(ℓ)
Applications
Caesium chromate was formerly used in the final stages of creating vacuum tubes. Therein, caesium vapour was produced by reaction of caesium chromate with silicon, boron, or titanium as reducing agents. The vapour was then added to the tube to react with and remove remaining gases, including nitrogen and oxygen.{{citation | title = Nature's Building Blocks: An A-Z Guide to the Elements | first = John | last = Emsley | year = 2001 | publisher = Oxford University Press | url = https://books.google.com/books?id=j-Xu07p3cKwC&q=%22Caesium+chromate%22+date:1950-2007&pg=RA1-PA81 | isbn = 0-19-850340-7 | page = 81}}.
References
{{reflist}}
{{Caesium compounds}}
{{Chromates and dichromates}}
{{DEFAULTSORT:Caesium Chromate}}