碘量法测定六价铬镀液中的三氧化铬和三价铬

摘要

The traditional method for analysis of CrO3 and Cr(III) in Cr(VI) plating bath was improved. The initial CrC>3 content is determined by iodimetry. The Cr(III) is oxidized to Cr(VI) by (NH4)2S2O8 under a weakly acidic condition without AgNO3 as catalyst. The total quantity of Cr(VI) is determined by iodimetry, and the content of Cr(III) is calculated by subtracting the initial Cr(VI) content from the total quantity of Cr(VI). The Cr(III) content determined by the method is agreed with that determined by (NH4)2Fe(SO4)2 titration after oxidation in a strongly acidic media with AgNO3 as catalyst. The precision of the method meets the practical production requirement. The method has advantages of simple operation, stable standard solution, and low cost.%改进了六价铬镀铬溶液中三氧化铬和三价铬的分析方法.先用碘量法测定三氧化铬的浓度,然后在弱酸性条件下,不加硝酸银作催化剂,用过硫酸铵将三价铬氧化成六价铬,用碘量法测定六价铬的总量,减去镀液中初始六价铬的量,即得到三价铬的质量浓度.该方法与硝酸银催化强酸性氧化后硫酸亚铁铵滴定法的三价铬测定结果基本一致,精度符合实际生产要求,但操作更为简单,标准溶液更稳定,成本更低.