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Free energies of transfer of alkali halides from water to urea-water mixtures at 25°C from EMF measurements
Authors:Asim K. Das  Kiron K. Kundu
Affiliation:(1) Physical Chemistry Laboratories, Jadavpur University, 700032 Calcutta, India
Abstract:The standard potentialssEo of M/M+ (M=Li, Na, K, Rb, and Cs) electrodes in aqueous urea solutions containing 12, 20, 30 and 37% by weight of urea have been determined at 25°C from emf measurements on the cell M(Hg)/MCl (m), solvent/AgCl–Ag, from the activities of metals in amalgams by use of a similar type of cell in water, and from the values ofsEo of the Ag/AgCl electrode determined earlier. The standard free energies of transfer of MCl, DeltaGto(MCl), from water to the mixed solvents, computed by use of these values and those for the Ag–AgCl electrode, rise sharply from Li+ to Na+ but fall from Na+ to K+ and rather sharply from K+ to Cs+ with a maximum at Na+ in all the solvent compositions. This has been attributed to the superimposition of ldquosoft-softrdquo interactions on the ldquoelectrostatic interactionsrdquo between the ions and the negative charge centers of the possible hydrogen-bonded solvent complexes in the mixed solvents. Comparison of DeltaGto(i) values for individual ions, obtained by a ldquosimultaneous extrapolationrdquo procedure, with those in aqueous mixtures of methanol,t-butanol, and dimethyl sulfoxide leads to the conclusion that the solvation of these ions in all these solvents is chiefly dictated by the ldquoacid-baserdquo type of ion-solvent interactions.
Keywords:Standard potential  alkali metal/metal ion electrodes  urea-water mixtures  free energies of transfer  alkali metal chlorides    /content/u8856254j3480qw7/xxlarge8220.gif"   alt="  ldquo"   align="  MIDDLE"   BORDER="  0"  >acid-base  /content/u8856254j3480qw7/xxlarge8221.gif"   alt="  rdquo"   align="  MIDDLE"   BORDER="  0"  > type of ion-solvent interactions
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