Potassium Chromate, K₂CrO₄

Potassium Chromate, K₂CrO₄, is usually prepared from the dichromate (vide infra) by neutralisation of the excess of CrO₃ above that necessary to form the normal salt, e.g. by potassium carbonate in aqueous solution; by fusion of the dichromate with potassium nitrate or potassium carbonate, and extraction with water; by interaction of potassium dichromate with ammonium chloride or sodium hydrogen phosphate.

Potassium chromate is yellow in colour, and crystallises in the rhombic system (bipyramidal):

a:b:c = 0.5694:1:0.7298,

and is isomorphous with potassium sulphate. It has a density of 2.741, a specific heat of 0.189, and melts at 971° C. The solid exists in two crystalline modifications, the a form being stable above, and the β form stable below, a transition temperature of 666° C. The solubility of potassium chromate in water is as follows:

Temperature, ° C.	Grams K2CrO4 in 100 Grams Water.
-11.35	54.54
0	57.11
30	65.13
60	74.60
105.8	88.8

The aqueous solution of potassium chromate has a sharp metallic taste, is poisonous, and exhibits an alkaline reaction. The freezing- point of a saturated solution is -11.35° C., and the boiling-point 105.8° C. Potassium chromate is soluble in solutions of potassium sulphate; it is insoluble in alcohol. Its solution is readily reduced by the usual agents on treatment with weak acids, with ammonium chloride, or with certain other salts.