DETERMINATION OF THE TRANSFER THERMODYNAMIC FUNCTIONS FOR THE ZINC(II), CADMIUM(II), MERCURY(II) AND MERCURY(I) IONS FROM WATER TO METHANOL, DIMETHYL-SULFOXIDE, ACETONITRILE, PYRIDINE AND N,N-DIMETHYLTHIOFORMAMIDE AND OF STANDARD ELECTRODE-POTENTIALS OF THE M2+/M(S) COUPLES IN THESE SOLVENTS

The transfer thermodynamic functions for the zinc, cadmium, mercury(II) and mercury(I) ions from water to methanol, dimethyl sulfoxide, acetonitrile, pyridine and NN-dimethylthioformamide are reported. The DELTA(t)G(THETA) values are calculated from potentiometrically determined standard electrode potentials in the different solvents with a silver reference electrode, and the DELTA(t)H(THETA) values are obtained from calorimetrically determined enthalpies of solution of the anhydrous metal trifluoromethylsulfonates. The entropies of transfer, DELTA(t)S(THETA), are calculated from the experimentally obtained DELTA(t)G(THETA) and DELTA(t)H(THETA) values; all of the measurements were performed at 25-degrees-C. The extrathermodynamic tetraphenylarsonium tetraphenylborate (TATB) assumption has been applied in order to calculate the contributions from the single ions. The studied ions are more strongly solvated in N,N-dimethylthioformamide, pyridine and dimethyl sulfoxide than in water, while they are more weakly solvated in methanol and acetonitrile. The entropies of transfer are negative for all the systems under study except for the cadmium ion to N,N-dimethylthioformamide.