Zur Polarographie von Niob und Tantal

Abstract

Abstract The polarographic behaviour of Nb V and Ta V in aqueous solvent systems does not allow a simultaneous determination of the two metals in presence of each other, therefore some organic solvents have been investigated. Characteristic waves have been obtained for Nb V in acetonitrile and for Nb IV in dimethylformamide. Melts of the system NaCl‐KCl‐AlCl 3 proved to be much more favourable however. NbCl 5 and TaCl 5 as solutes are present in such melts as monomolecular species and their products of hydrolysis, if any, are converted into the pentachlorides by AlCl 3 , one of the components of the solvent. In this kind of melt Nb V yields a polarographic double wave (Nb V → Nb IV → Nb III ) and Ta V a single wave (Ta V → Ta III ). The half wave potentials of the reductions of the two metals differ by 500 millivolts.