三氯化钛还原——重铬酸钾滴定法测定铁酸钙中Fe2O3

Determination of Fe2O3 in Calcium Ferrite by Titanium Trichloride Reduction-Potassium Dichromate Titration

试样以硫磷混酸溶解后,加盐酸铁转化为氯化铁,首先用Sn Cl2预还原大部分Fe3＋为Fe2＋,然后用Ti Cl3定量还原剩余的Fe3＋为Fe2＋,以钨酸钠为指示剂作指示还原终点,即当Fe3＋定量还原为Fe2＋后,过量一滴Ti Cl3溶液时,可使作为指示剂钨酸钠中的六价钨（无色）还原成蓝色的五价钨化合物,故溶液呈显蓝色。过量的Ti Cl3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Ti Cl3还原剂的影响。避免了国标法及经典法的无汞测铁元素分析方法用重铬酸钾氧化过量Ti Cl3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。

The was added to c sample was dissolved by sulfuric and hange iron into ferric chloride. Now, phosphoric mixed acid, then the hydrochloric acid SnCI2 was used to pre-reduee most of Fe3＋ to Fe2＋ , after that, TiCI3 was used to quantitatively reduce the rest of Fe3＋ to Fe2＋, indicator to indicate the destination of reduction, that is to say, after Fe3＋ taking sodium tungstate as the was quantitatively reduced to Fe2＋ , when a drop of excessive TiCI3 solution was added, and the hexavalent tungsten （colorless） in the indicator of sodium tungstate was reduced to a blue pentavalent tungsten compound, so the solution showed blue. Under the catalysis of excessive copper sulfate, the bule color faded by the oxidation of the dissolved oxygen in water and the free oxygen in air, thereby the influence of excessive TiC13 reducing agent could be eliminated. Thus, the errors, easy imported when the excessive TiC13 was oxidized by potassium dichromate according to the mercury-free iron element analysis method in national standard method and classical method, were avoided. In the medium of sulfuric and phosphoric mixed acid, with diphenylamine sulfonate as an indicator, the standard solution of potassium dichromate was used to titrate the content of total iron, and the satisfactory results were obtained.