| Popis: |
The specific adsorption of chloride, bromide, iodide, azide, and thiocyanate has been studied at an electropolished polycrystalline silver-aqueous interface using differential capacitance measurements. For chloride, bromide, and azide, quantitative estimates of the surface concentration of specifically adsorbed anions were obtained from capacitance-potential data in mixed fluoride electrolytes having a constant ionic strength of 0.5. The dependence of the measured capacitance upon the ionic strength of sodium fluoride was also investigated in order to check the behavior of the polycrystalline surface in comparison with the predictions of conventional double-layer models. Estimates of the specifically adsorbed charge densities of chloride, bromide, and thiocyanate anions were also obtained from a “kinetic probe” technique which entailed monitoring the response of the outer-sphere reduction rate of CO(NH3)5F2+ and Co(NH3)63+ to the addition of the appropriate adsorbing anion. At the average potential of zero charge for the polycrystalline silver surface, the standard free energies of adsorption − Δ3o for chloride, bromide, and azide were found to be within ca. 5 kJ mol−1 of the corresponding quantities obtained at mercury electrodes. However. significantly greater increases in − Δ3o in the sequence Cl− |
