8.42.Approximate the expected voltage for the following
electrochemical reaction using (a)the given molal concentra-
tions and (b)the calculated activities using simple Debye-
Hückel theory. The value of å for both Zn^2 and Cu^2 is 6
10
10 m.
Zn (s) Cu^2 (aq, 0.05 molal) →
Zn^2 (aq, 0.1 molal) Cu (s)
Explain why you get the answers you do.
8.43. (a)Explain why it is important to specify an identity of
the anion in Example 8.12 even though it is a spectator ion.
(b)Recalculate part b of Example 8.12, assuming that the
salts are both sulfate salts rather than nitrate salts. Consider
the concentrations given in the example as the resultant cation
concentration, not the concentration of the salt itself.
8.44.Is equation 8.40 supported by Table 8.3? Explain your
answer.
8.8 Transport and Conductance
8.45.Show that equation 8.61 gives units of amperes, a unit
of current. You will have to use equation 8.5 to get proper
units for the electric field E.
8.46.(a) The salt NaNO 3 can be thought of as NaCl
KNO 3
KCl. Demonstrate that 0 values show this type of
additivity by calculating 0 for NaNO 3 from the 0 values of
NaCl, KNO 3 , and KCl found in Table 8.4. Compare your cal-
culated value with the 0 value for NaNO 3 in the table. (b)
Predict approximate 0 values for NH 4 NO 3 and CaBr 2 using
the values given in Table 8.4.
8.47.In a galvanic cell, determine whether I and I are
moving toward the cathode or the anode. How about for an
electrolytic cell?
8.48.What is the estimated velocity for Cu^2 ions moving
through water in a Daniell cell in which the electric field is
100.0 V/m? Assume that å for Cu^2 is 4 Å and the viscosity of
water is 0.00894 poise. Comment on the magnitude of your
answer.
8.49.Set up an expression that evaluates the force on two
unit charges of opposite sign at varying distance in vacuum
and in a medium having some dielectric constant r. Then,
evaluate the force between the two charges at distances rang-
ing from 1 Å to 25 Å in 1-Å increments. How do the values
vary between a vacuum and some medium with a nonzero di-
electric constant? Do the same evaluations for charges of same
sign, and compare the results with charges of opposite sign.
8.50.A Daniell cell is constructed with all standard concen-
trations except for Zn^2. The concentration of the zinc ion has
values of 0.00010 M, 0.0074 M, 0.0098 M, 0.0275 M, and
0.0855 M. What are the Evalues of the cell? What trend do
the Evalues show?
8.51.Ionic salts are composed of ions that can have charges
of up to 4 and 3. Construct a table of ionic strengths that
tabulate Iversus ion charge for every possible combination, as-
suming a 1-molal solution of each salt.
8.52.Calculate (a)the solubility product constant for Ag 2 CO 3
and (b)the value for Kwusing the following data:
Ag 2 CO 3 (s) 2e^ →2Ag (s) CO 32
(aq)
E1/20.47 V
Ag^ (aq) e^ →Ag (s) E1/20.7996 V
O 2 (g) 2H 2 O () 4e^ →4OH^ (aq) E1/20.401 V
O 2 (g) 4H^ (aq) 4e^ →2H 2 O () E1/21.229 V240 Exercises for Chapter 8
Symbolic Math Exercises