Physical Chemistry Third Edition

8.5 Thermodynamic Information from Electrochemistry 377

8.23 a.Find the solubility product constant for lead(II) chloride
at 298.15 K.
b. Find the molality of chloride ions in a saturated aqueous
solution of lead(II) chloride at 298.15 K.
c.Find the molality of lead(II) ions in a saturated aqueous
solution of lead(II) chloride at 298.15 K if 0.100 mol of
sodium chloride has been added per kilogram of water.

8.24 Using electrochemical data, find the value ofKw, the
ionization constant of water, at 298.15 K.

8.25 a.Find the value ofKspfor Ag 2 S at 298.15 K.

b. Find the molality of S^2 −in a saturated solution of Ag 2 S

in water at 298.15 K.

c.Find the molality of S^2 −at 298.15 K in a saturated

solution of Ag 2 S that contains 0.1000 mol kg−^1 of

AgNO 3. Use the Davies equation to approximate

activity coefficients.

8.26At 298.15 K the solubility product constant for PbS is
quoted as 6. 5 × 10 −^34. Find the value ofE◦for the
half-reaction at 298.15 K:

PbS(s)+ 2 e−−→Pb(s)+S^2 −

8.27 The solubility product constant of HgS is variously cited
as being equal to values between 4× 10 −^53 and
2 × 10 −^49. Find the largest and smallest value of the
standard reduction potential for the following half-reaction
that could correspond to these values:

HgS(s)+ 2 e−−→Hg(l)+S^2 −

8.28 a.Using half-cell potentials, find the value of the
equilibrium constant at 298.15 K for the reaction

Hg 2 Cl 2 (s)+2Ag+
Hg^22 ++2AgCl(s)

b. Calculate∆G◦and the equilibrium constant using

Gibbs energies of formation, and compare your value

with the value from part a.

c.Calculate the equilibrium values of the molalities of

Ag+ions and Hg^22 +ions. Remember the solubility

product constants.

8.29 a.Find the value at 298.15 K of the solubility product
constant for PbSO 4 in water.
b. Find the molality of SO^24 −ions in a saturated solution
of PbSO 4 in water at 298.15 K.
c.If 0.200 mol of NaNO 3 is added to the saturated
solution per kilogram of water, what will be the effect
on the solubility of PbSO 4? Give a qualitative verbal

answer, explaining your reasoning. If there is a change,

calculate the new molality of SO^24 −at saturation.

d.If 0.100 mol of solid Pb(NO 3 ) 2 per kilogram of water is

added to the original saturated solution (no sodium

nitrate present), what will the new molality of SO^24 −be

at saturation?

8.30a. Using electrochemical data, find the formation constant

at 298.15 K for the complex ion AuCl− 4 , which is the

equilibrium constant for the reaction

Au^3 ++4Cl−
AuCl− 4

b. Find∆G◦for the reaction.

c.If 0.200 mol of AuCl− 4 is added to 1.000 kg of water,

find the equilibrium concentration of Cl−ions.

8.31 Find the solubility product constants at 298.15 K for

a.Hg 2 Cl 2

b.Ag 2 S

8.32 Find the solubility product constants at 298.15 K for

a.PbSO 4

b.AgBr

8.33a. Find the equilibrium constant at 298.15 K for the

reaction

2Ce^4 ++2Cl−
2Ce^3 ++Cl 2 (g)

b. Find the equilibrium composition if a 0.0500 mol kg−^1

solution of CeF 4 is added to an equal volume of a

0.0500 mol kg−^1 solution of NaCl at 298.15 K. Assume

that the chlorine gas is maintained at pressureP◦and

use the Davies equation to estimate activity coefficients.

8.34 Find the equilibrium constant at 298.15 K for the reaction

I 2 (s)+2Cl−
2I−+Cl 2 (g)

8.35 Find the equilibrium constant at 298.15 K for the reaction

AgCl(s)+Br−
AgBr(s)+Cl−

8.36 The solubility product constant of PbS at 298.15 K is

quoted as 3. 4 × 10 −^28. From this value calculate the

standard reduction potential at 298.15 K of the

half-reaction

PbS(s)+ 2 e−−→Pb(s)+S^2 −

To see how reliable literature values can be, compare your

answer with that of Problem 8.26.