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214 CHAPTER 2

4. The heat of the chloride ion interaction with water is measured to be
, in which the contribution of the Born charging process is
If the dielectric constant of water at 298 K is 78.3, estimate its rate of change
with temperature at this temperature. Also calculate the percent error introduced
in the Born charging term if the dielectric constant is assumed to be independent
of temperature. Consider and (Contractor)
–
5. When an F comes in contact with water molecules, its ion–quadrupole interac-
tion energy is Calculate the quadrupole moment of water
(Contractor)

6. If the total primary hydration number of NaCl in a 1 M solution is 6, make a
rough calculation of the dielectric constant of the solution by assuming that the
dielectric constant of pure water is 80 and that of the water molecule in the
primary hydration sheath is 6.
7. For an NaCl solution, calculate the concentration at which the so-called “Gurney
co-sphere” is reached. (Hint: For 1:1 electrolyte, the average separation l (in Å)
where c is the concentration in mol Assume the Gurney
co-sphere is two water molecules beyond the ions periphery.) (Xu)
8. Suppose the results from Exercise 7 are true and calculate the solvation number
for NaCl. Comment on the reliability of the result. (Xu)
9. (a) A Roman spectrum shows that in a 4.0 M NaCl solution, about 40% of the
waters are in the primary sheath. Estimate the solvation number (b) If the SB
region consists of only one layer of water molecules, is there any bulk water left
in this solution? (Xu)
10. Solvation numbers for and CF have been measured at about 5 and 1,
respectively. With this information, and recalling that the number of moles per
liter of pure water is 55, calculate the dielectric constant of a 5 M solution of
NaCl. (The dielectric constant of pure water is to be taken as 80 near room
temperature; when the water molecules are held immobile in respect to the
variations of an applied field, M drops to 6.)
11. Calculate the sum of the heats of hydration of and The lattice energy is
The heat of the solution is
12. Using the Born equation as representing a part of the free energy of hydration
of ions, derive an expression for the entropy of Born hydration. According to
this, what would be the entropy of Born solvation of the ion with a radius of
200 pm?
13. Calculate the ion–solvent interaction free energy for and in
water. The ionic radii are 133, 99, 136, and 181 pm, respectively, and the
dielectric constant for water is 78.3 at 25°C. (Kim)