Ammonium Chromate, (NH₄)₂CrO₄

Ammonium Chromate, (NH₄)₂CrO₄, is formed when a solution of chromic acid is neutralised by ammonia, and the mixture evaporated. It yields golden-yellow needles (monoclinic prisms):

a:b:c = 1.9603:1:1.2226; β = 115° 13',

of density 1.886, and soluble in water. On heating or on exposure to air they decompose, evolving ammonia, and form the dichromate:

2(NH₄)₂CrO₄ = (NH₄)₂Cr₂O₇ + 2NH₃ + H₂O;

consequently the chromate cannot be dried at 100° C. without undergoing decomposition.