Potentiometric study on the activity coefficients in equimolal mixtures of some divalent metal perchlorates in acetonitrile solution

Abstract

E ectromotive force measurements of cells of the type Pt &∣ Cu(ClO4)2(m1), M(ClO4)2(m2), CuClO4(m3) ∣ Cu(ClO4)2(m), CuClO4(m3) ∣ Pt, where M ≡ Cd or Ni, and m = m1 + m2, at 25°C, have been used to derive the activity coefficient of copper(II) perchlorate in its equimolal mixtures with either cadmium(II) or nickel(II) perchlorates in acetonitrile solution in the presence of copper(I) perchlorate at low concentration. The fact that the activity coefficient remains constant, within the experimental error, when the composition of equimolal mixtures is varied, is ascribed to the existence of the divalent metals exclusively in the form of the [ML6]2+ complex cations (L = acetonitrile), whose interaction potentials are essentially independent of the nature of the central metal atoms.In an additional potentiometric study the equilibrium constant of the reaction Cu + Cu2+ ⇆ 2 Cu+ in acetonitrile solution has been determined.