‫سری دوم مهلت یک هفته‬-‫تمرینات الکتروشیمی جبرانی‬
1 Devise a cell in which the overall reaction is
Pb(s) + Hg2SO4(s) ―> PbSO4(s) + 2Hg(l)
What is its potential when the electrolyte is saturated with both salts at 25˚C?
2 A fuel cell develops an electric potential from the chemical reaction between
reagents supplied from an outside source. What is the zero-current potential of a cell
fuelled by (a) hydrogen and oxygen, (b) the combustion of butane at 1.0 atm and 298
K?
3 Hydrogen behaves imperfectly at high pressure, and its equation of state may be
summarized by the virial equation
pVm/RT = 1 + 5.37 Х 10-4 (p/atm) + 3.5 Х 10-8 Х (p/atm)2
The zero-current potential of the cell
Pt | H2(g) | HCl(aq, 0.10 mol kg-1) | Hg2Cl2(s) | Hg(l)
has been measured up to 1000 atm and good agreement between experiment and a
theoretical expression was achieved up to 600 atm on the assumption that the only
significant volume change was that associated with the hydrogen. Above 600 atm the
compressibility of the other components became significant. What is the cell potential
at 500 atm? (Use activity coefficients from Table 10.4.)
4 The fugacity of a gas can be determined electrochemically from the pressure
dependence of the reduction potential of a gas electrode. The zero-current potential of
the cell
Pt | H2(g, pο ) | HCl(aq, 0.010 mol kg-1) | Cl2(g, p) | Pt
was as follows at 298 K:
p/bar
E/V
1.000
1.5962
50.00
1.6419
100.0
1.6451
Calculate the fugacities of chlorine at the three pressures. (Use activity coefficients
from Table 10.4.)
5 The zero-current potential of the cell
Pt | H2(g, pο ) | HCl(aq, m) | Hg2Cl2(s) | Hg(l)
Has been measure with high precision, with the following results at 25˚C:
m/(mmol kg-1)
E/V
1.6077
0.60080
3.0769
0.56825
5.0403
0.54366
7.6938
0.52267
10.9474
0.50532
Find the standard potential of the cell and the mean activity coefficient of HCl at these
molalities. (Make a least-squares fit of the data to the best straight line.)
6 Careful measurements of the potential of the cell
Pt | H2(g, pο ) | NaOH(aq, 0.0100 mol kg-1), NaCl(aq, 0.01125 mol kg-1) | AgCl(s) | Ag
have been reported. Among the data is the following information:
θ/˚C
E/V
20.0
1.04774
25.0
1.04864
30.0
1.04942
Calculate pKw at these temperatures and the standard enthalpy and entropy of the
autoprotolysis of water at 25˚C.