Copper Chromates

Both cuprous and cupric chromates are known. The latter forms an ammoniacal salt, 2CuCrO₄.CuO.10NH₃, which is obtained on precipitating a green solution of basic copper chromate in ammonia by means of alcohol, as dark green needles which are unstable in air. The salt, CuCrO₄.4NH₃, also exists.

Three basic chromates have been described: (a) CuCrO₄.2CuO.2H₂O, a yellowish-brown precipitate obtained (together with some cupric dichromate) on mixing solutions of ammonium chromate and copper sulphate; (b) 2CuCrO₄.5CuO.5H₂O; and (c) CuCrO₄.6CuO.5H₂O.