Caesium chromate or cesium chromate is an inorganic compound with the formula Cs₂CrO₄. It is a yellow crystalline solid that is the

caesium Caesium (IUPAC spelling; also spelled cesium in American English) is a chemical element; it has Symbol (chemistry), symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of , which makes it one of only f ...

salt In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...

chromic acid Chromic acid is a chemical compound with the chemical formula . It is also a jargon for a solution formed by the addition of sulfuric acid to aqueous solutions of dichromate. It consists at least in part of chromium trioxide. The term "chromic ...

, and it crystallises in the

orthorhombic In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic Lattice (group), lattices result from stretching a cubic crystal system, cubic lattice along two of its orthogonal pairs by two different factors, res ...

system. Its major application in the past was for the production of caesium vapour during

vacuum tube A vacuum tube, electron tube, thermionic valve (British usage), or tube (North America) is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied. It ...

manufacture. Currently it is only used as the precursor for other compounds of academic interest.

Preparation

Caesium chromate is mainly obtained from the reaction of chromium(VI) oxide with

caesium carbonate Caesium carbonate or cesium carbonate is a chemical compound with the chemical formula . It is white crystalline solid. Caesium carbonate has a high solubility in polar solvents such as water, ethanol and DMF. Its solubility is higher in organic ...

, wherein

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

gas is evolved: : CrO₃(aq) + Cs₂CO₃(aq) → Cs₂CrO₄(aq) + CO₂(g) Alternatively,

salt metathesis A salt metathesis reaction (also called a double displacement reaction, double replacement reaction, or double decomposition) is a type of chemical reaction in which two ionic compounds in aqueous solution exchange their component ions to form two ...

between

potassium chromate Potassium chromate is the inorganic compound with the formula Potassium, K2Chromate ion, CrO4. This yellow solid is the potassium salt of the Chromate ion, chromate anion. It is a common laboratory chemical, whereas sodium chromate is important ...

and

caesium chloride Caesium chloride or cesium chloride is the inorganic compound with the formula Caesium, CsChloride, Cl. This colorless salt is an important source of caesium ions in a variety of niche applications. Its crystal structure forms a major structural ...

can be performed: : K₂CrO₄(aq) + 2 CsCl(aq) → Cs₂CrO₄(aq) + 2 KCl(aq) Finally, caesium dichromate (itself derived ''via'' salt metathesis from

ammonium dichromate Ammonium dichromate is an inorganic compound with the Chemical formula, formula (NH4)2Cr2O7. In this compound, as in all chromates and dichromates, chromium is in a +6 oxidation state, commonly known as hexavalent chromium. It is a salt consisting ...

) 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 Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...

boron Boron is a chemical element; it has symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the boron group it has three ...

, or

titanium Titanium is a chemical element; it has symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in ...

as reducing agents. The vapour was then added to the tube to react with and remove remaining gases, including

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

and

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

References

{{DEFAULTSORT:Caesium Chromate Caesium compounds Chromates