Polarography of europium in aqueous and aqueous methanolic solutions

The standard rate constants for the reduction of europium in perchlorate and chloride media and the formal rate constants in sulphate, acetate and lactate solutions are reported. The rate increases in the order of increasing polarisability of the anion or the increasing stability of the complex, viz., perchlorate < sulphate < lactate ≈ acetate. The effect of methanol on the polarography of europium has been studied. In perchlorate and chloride media, the half-wave potential shifts to negative values and then to positive values as the methanol content is increased. In acetate solutions, the shift is continuously to negative potentials. This is attributed to the effect of complex formation in acetate media and ion-pairing in perchlorate and chloride media. The effect of viscosity on the diffusion current was found to obey the Stokes-Einstein equation