Caesium chromate

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.

Caesium chromate

Names
IUPAC name Caesium chromate
Other names Dicaesium chromate
Identifiers
CAS Number	13454-78-9
3D model (JSmol)	Interactive image
ChemSpider	55521
ECHA InfoCard	100.033.296
EC Number	236-640-4
PubChem CID	61613
CompTox Dashboard (EPA)	DTXSID20894903
InChI InChI=1/Cr.2Cs.4O/q;2*+1;;;2*-1/rCrO4.2Cs/c2-1(3,4)5;;/q-2;2*+1 Key: BROHICCPQMHYFY-UICSPCLAAP
SMILES [Cs+].[Cs+].[O-][Cr]([O-])(=O)=O
Properties[1]
Chemical formula	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)
Solubility in water	45.50 g/100 g (25 °C)
Structure
Crystal structure	orthorhombic
Space group	Pnma (№ 62)
Lattice constant	a = 8.368 Å, b = 6.226 Å, c = 11.135 Å
Formula units (Z)	4
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	highly toxic, carcinogenic, oxidiser, environmental hazard
GHS labelling:
Pictograms
Flash point	Non-flammable
Related compounds
Other anions	Caesium sulfate
Other cations	Sodium chromate Potassium chromate Ammonium chromate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Its major application in the past was for the production of caesium vapour during vacuum tube manufacture.^[2] Currently it is only used as the precursor for other compounds of academic interest.^[3][4]

Preparation

Caesium chromate is mainly obtained from the reaction of chromium(VI) oxide with caesium carbonate, wherein carbon dioxide gas is evolved:^[3]

CrO₃(aq) + Cs₂CO₃(aq) → Cs₂CrO₄(aq) + CO₂(g)

Alternatively, salt metathesis between potassium chromate and caesium chloride can be performed:^[4]

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:^[2]

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.^[5]