三氯化钛还原重铬酸钾滴定法测定锆铁中铁

Determination of Fe in ferroziconium by potassium dichromate reduction titration with titanium trichloride

以王水、氢氟酸溶解试样后，硫磷混酸冒烟驱除去硅和氟，加盐酸使铁转化为氯化铁。首先用氯化亚锡预还原大部分Fe^3＋为Fe^2＋，然后用TiCL3定量还原剩余的Fe^3＋和Fe^2＋，以钨酸钠作指示剂指示还原终点，即当Fe^3＋定量还原为Fe^2＋后，过量一滴TiCL3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，故溶液呈蓝色。过量的TiCL3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TiCL3还原剂的影响。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铁量，结果满意。

The sample is dissolved by aqua regia and hydrofluoric acid, then silicon and fluorine are removed by smoking with sulfuric phosphoric acid, and the hydrochloric acid is added to translate ferric into ferric chloride. First, the stannous chloride is used to prereduce most of Fe^3＋ into Fe^2＋ , and the quantitative TiCL3 is used to reduce the residual Fe^3＋ and Fe^2＋ ,with sodium tungstate as an indicator to point the reducing end, that is to say, when all Fe^3＋ is reduced into Fe^2＋ , a excessive drop of TiCL3 solution can reduce the hexavalent tungsten （colorless） in sodium tungstate into the blue pentavalent tungsten compounds, so the solution presents blue. Catalyzed by copper sulfate, the excess TiCL3 is oxidized by the dissolved oxygen in water and the free oxygen in air, then the tungsten blue faded gradually, thus the influence of excess TiCL3 reducing agent is eliminated. Within the sulfuric phosphoric acid, taking sodi- um diphenylaminesulfonate as an indicator, the content of ferric is titrated by potassium dichromate stand- ard solution, reaching a satisfactory result.