The polarographic behavior of metal ions in molten LiNO3-KNO3 eutectic in presence of complexon III

Abstract

The possibility of using complexon III as a complexing substance in the polarography of salt metls (LiNO3-KNO3 eutectic) has been investigated. Complexon III was found to form complexes with Cd, Pb, Ni and Zn ions in the ratios 1:2 for Cd and Pb, 2:1 for Ni and 1:1 for Zn. Cadmium and lead complexes can be reduced at the DME with E1/2=-0.70 V for the cadmium complex and E1/2=-0.59 V for the lead complex (vs. a calomel reference electrode). Diffusion coefficients D=1.5×10-6 cm2 s-1 and D=2.5×10-6 cm2 s-1 were found for non-complexed cadmium and lead ions, respectively. Complexes of cadmium and lead with complexon III gave values of D=3.0×10-7 cm2 s-1 and D=3.7×10-7 cm2 s-1, respectively, at 170°C. The activation energy of the complexed and non-complexed Cd ion diffusion current Q=4.50 kcal mol-1 and the heterogenous electrode process rate constants ke0=2.5×10-6 cm s-1 for the complexed ion have been determined.