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试样以硫磷混酸溶解后,加盐酸使铁转化为氯化铁,首先用SnCl_2预还原大部分Fe~(3+)为Fe~(2+),然后用TiCl。定量还原剩余的Fe~(3+)为Fe~(2+),以钨酸钠作指示剂还原终点,即当Fe3+定量还原为Fe~(2+)后,过量一滴TiCl_3溶液时,可使作为指示剂的钨酸钠中的六价钨(无色)还原成蓝色的五价钨化合物,故溶液呈显蓝色。过量的TiCl_3可在硫酸铜的催化下,借水中溶解氧及空气中的游离氧氧化使钨蓝色泽褪去,从而消除过量TiCl_3还原剂的影响。避免了国标法及经典法的无汞测铁分析方法用重铬酸钾氧化过量TiCl_3时易引入的误差。在硫磷混酸介质中,以二苯胺磺酸钠为指示剂,用重铬酸钾标准溶液滴定全铁量,取得了令人满意的结果。
After the sample was dissolved with phosphoric acid and phosphoric acid, hydrochloric acid was added to convert the iron to ferric chloride. First, most of Fe 3+ was pre-reduced to Fe 2+ with SnCl 2, and then TiCl was used. The rest of Fe (3+) was quantitatively reduced to Fe 2+, and the end point was reduced with sodium tungstate as indicator. That is, when a drop of TiCl 3 solution was overdone after the Fe 3 + was quantitatively reduced to Fe 2+, The hexavalent tungsten (colorless) in sodium tungstate as an indicator was reduced to a blue pentavalent tungsten compound so that the solution appeared blue. Excess TiCl_3 can be catalyzed by copper sulfate, which can eliminate the influence of excess TiCl_3 reductant by dissolving oxygen in water and free oxygen in air to fade the blue color of tungsten. Avoid the national standard method and the classic method of mercury-free determination of iron with potassium dichromate oxidation TiCl_3 excessive error introduced easily. In phosphoric acid and phosphoric acid mixed medium, sodium diphenylamine sulfonate is used as an indicator to titrate all iron with potassium dichromate standard solution, and satisfactory results have been obtained.