用五价钼为库仑滴定剂测定铈、铬和钒

COULOMETRIC TITRATION WITH PENTAVALENT MOLYBDENUM——DETERMINATION OF CERIUM,CHROMIUM AND VANADIUM

五价钼可用作库仑滴定剂,在4.5M硫酸,0.1M钼酸铵之混合介质中,电流密度在每平方厘米1毫安到10毫安之间;或在3M硫酸,0.05M钼酸铵介质中,电流密度在每平方厘米3毫安至7毫安之间,电流效率均可达到100%.我们用五价钼测定了高价的铈、铬和钒.测定在室温进行,空气中的氧不干扰测定.当铈、铬和钒的量分别在12.3毫克0.05—2.5毫克和0.5—2.5毫克范围内时,误差均在0.2%以内.铜离子对测定有干扰,但通入氮气后干扰可以消除.

ABSTRACT The use of electrolytically generated pentavalent molybdenum as a coulometric titrant has been studied.The current efficiency for the electrogeneration of molybdenum(V) at a platium cathode in sulfuric acid media was found to be a function of the generating current density and the concentration of haxavalent molybdenum in various concentration of sulfuric acid.With 4.5 M sulfuric acid containing 0.1 M ammonium molybdate the generation of molybdenum(V) is of 100 per cent efficiency up to a current density of 1—10 milliamp/cm^2.With this medium milligram quantities of cerium,chromium and vanadium can be titrated coulometrically with an average error of about ±0.2 per cent or less.Cooke's modified potentiometric method was used for end-point detection. In the presence of copper,the test solution must be free from air by bubbling with and titrating under nitrogen,as copper catalyzed the aerial oxidation of molybdenum(V).