Potassium Chlorochromate, CrO₂.OK.Cl

Potassium Chlorochromate, CrO₂.OK.Cl, may be obtained (a) by warming together a mixture of potassium dichromate and concentrated hydrochloric acid; (b) by the action of chromyl chloride upon a solution of potassium chloride or upon aqueous potassium chromate acidified with acetic acid; (c) by fusion of potassium dichromate with chromic chloride; or (d) by interaction of phosphorus trichloride and potassium dichromate.

Potassium chlorochromate crystallises in the monoclinic system (prismatic):

a:b:c = 0.9653:1:1.0174; β = 90° 20',

isomorphous with the corresponding ammonium salt. The crystals are brownish red in colour, have density 2.497, and are decomposed by fusion:

4CrO₂.OK.Cl = K₂Cr₂O₇ + Cr₂O₃ + 2KCl + Cl₂ + O₂.

With sulphuric acid, chromyl chloride is produced.

Rubidium Chromate, Rb₂CrO₄, crystallises in the bipyramidal class of the rhombic system:

a:b:c = 0.5665:1:0.7490;

it is obtained by interaction of chromic acid and rubidium carbonate, or fusion of chromium sesquioxide with rubidium nitrate. The double salt, Rb₂Mg(CrO₄)₂.6H₂O, has been prepared.