No abstract

The relation of the " medium effect " or " solvent activity coefficient " to the directly measurable real free energy of transfer is discussed. Measurements of the latter quantity for solutions in aqueous solvents containing methanol, ethanol, dioxan, acetone, ethylene glycol, formamide or dimethyl sulphoxide are reported and discussed. The surface composition of the solvent mixture is accessible and this information can be used to set reasonable limits on the possible value of the " medium effect ". Thus it can be shown that some assignments of single ion medium effects based on oversimplified models of solvation are inadequate. The assignment based on the neglect of liquid junction potentials between solvents is often surprisingly good.

Dehydration of Hydrated Ions in Solution 1245 C112O is 23 kcal/mol while for CuO is 25 kcal/mol. This latter oxide is partly reduced to CU2O at least on the surface, due to the pretreatment adopted in catalysis (480°, 4 hr, 10-5 Torr). Consequently, its activity and its Ea are attributed to Cu+ .14 On the other hand, the Ea values obtained for the MCu specimens clearly resemble that found on CU2O. In these specimens the Cu+ content, formed during the outgassing treatment, can be evaluated by the esr methods only indirectly. In Table III an attempt to correlate the amount of Cu+ formed and the catalytic activity of some MCu specimens is made. The table reports the fraction of surface sites occupied by Cu+ ions, calculated from the decrease of Cu2+surface per unit surface area together with the absolute rate constant (kaba) at 350°for the N2O decomposition. It may be noted that the amount of reduced Cu+ formed parallels the increase in activity, thus suggesting that the main active sites in the N2O decomposition can be identified as Cu+ ions.