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ION–SOLVENT INTERACTIONS 219

the trend and the sign of What is the driving force of the solution process
in case (Xu)
12. Chloride is surrounded by 4 water molecules. Calculate the ion–dipole interac-
tion work (Contractor)
13. Anomalous salting in is said to occur when the dipole moment of water is greater
than that of the organic molecule concerned, but the solubility of the latter
increases when ions are added to the solution. What kind of model could explain
the observation that anomalous salting in occurs when the electrolyte consists
of large ions?

From the model you derive, calculate the minimum radius of ions required to
salt-in benzoic acid in a 1 M solution of electrolyte. (Take the polarizability as
where is the radius of any entity involved.)
14. An ion of charge and radius r is transferred from a solvent of dielectric
constant to a solvent of dielectric constant Derive an expression for the
free-energy change associated with this transfer using the Born model. (Con-
tractor)
15. What is the free-energy change involved in transferring from water to a
nonpolar medium like carbon tetrachloride with a dielectric constant of 2.23 at
298 K? Is this an energetically favorable process? (Make use of Problem 3.)
Water has a dielectric constant of 78.54 at 298 K. (Contractor)
16. Living cells are surrounded by membranes and on either side of the membrane
an aqueous environment is present. The interior of the membrane is highly
nonpolar. Based on the result of Problem 15, can you explain why it is difficult
to transport or move charges across a membrane in a living cell? (Contractor)
17. For a given water molecule, what is the maximum number of hydrogen bonds
that can be formed with other neighboring water molecules? Are these hydrogen
bonds identical in bonding nature for this particular water molecule? Why? If
there is a difference in bonding nature for these hydrogen bonds, how would you