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. |