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A faradaic impedance study has been made of the reduction of Cd(II) ions from a 1 M KF base electrolyte at the DME. It could be shown that only the Cd(II) present in the solution and the end product, viz. Cd(Hg), are the diffusing partmles and that intermediates are present only at the interface. From the analysis of the impedance data it followed that at the interface the Cd(II) species is first subject to a heterogeneous chemical transfer and thereafter is reduced according to two discrete one-electron transfers, both obeying the Butler--Volmer equation. The kinetm parameters of the steps are reported. A number of other conceivable mechanisms were considered, but fortunately they all either could be defimtely ruled out or were found to be less acceptable.

A method for the estimation of standard chemical potential differences (Ap') of single ions for the transfer from one solvent to another, described previously, is further improved and applied to the transfer from water to acetone and acetone-water mixtures.With some reservation a value of the surface potential x of acetone is derived.

E.m.f.-measurements on cells of the type: Hg/HgzClz/saturated KCI-soh.(aq.)/standard buffer soln./saturated KCl-soln.(aq.)/HgzClz/Hg, using standard buffer solutions in methanol-water and ethanol-water mixtures and liquidjunction forming devices of different design, showed that, for three different boundary-types, the liquid-junction potentials are identical within experimental error.E.m.f.-measurements on cells of the type: glass electrode/standard buffer soln./saturated KCl-soIn.(aq.)/HgzClz -Hg, using succinate standard buffer solutions in methanol-water and ethanol-water mixtures and different types of glass electrodes, proved that the variation of the standard potential of these glass electrodes with the composition of the alcohol-water mixture does not depend on the type of glass electrode. Theoretical PartIn alcohol-water mixtures (as in water), the electrometric method of pH-determination is based upon the measurement of the electromotive forces Es and EX of the cells: glass electrode/standard buffer soh. S/saturated KCI (as./ glass electrode/"unknown" soh. X/saturated KCI (aq.)/ reference electrode (I) reference electrode (11)* Address: Croesestraat 77A, Utrecht.

In the diffusion through the boundary layer between electrolyte solutions in diferent media, the transport of uncharged particles comes into play. The contribution of this transport to the diffusion potential is measured for alkali halide solutions in methanol-water mixtures. Using A$-values of individual ions in methanol-water mixtures, the total diffusion potentials are calculated.It can be concluded that the diffusion potential between electrolyte solutions in different solvents depends mainly on the primary medium effect.

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A method for the estimation of standard chemical potential differences (Ap") of single ions for the transfer from one solvent to another, derived previously, is applied to the transfer of ions from water to ethanol and ethanol-water mixtures.A similar method is used to estimate the standard partial molar enthalpy of transfer, AH' of single ions, and from these data values for the standard partial entropy of transfer, ASo are obtained.The difference between the standard real potentials of the chloride ion in ethanol and in water has been determined by Case and Parsons. From these data, the corresponding value of Ap' and the surface potential of water, the surface potential of ethanol is determined.