Electrochemistry

1
Electrochemistry
1. Balance each of the following RedOx reactions occurring in acidic conditions:
a. Fe2+
(aq) + MnO4
1-
(aq) → Fe3+
(aq) + Mn2+
(aq)
b. Br2(l) + SO2(g) → Br1-
(aq) + SO4
2-
(aq)
c. Cu(s) + NO3
1-
(aq) → Cu2+
(aq) + NO2(g)
d. HgS(s) + Cl1-
(aq) + NO3
1-
(aq) → HgCl4
2-
(aq) + NO2(g) + S(s)
e. Cl2(g) → ClO3
1-
(aq) + Cl1-
(aq)
2. Balance each of the following RedOx reactions occurring in basic conditions:
a. MnO4
1-
(aq) + NO2
1-
(aq) → MnO2(s) + NO3
1-
(aq)
b. Zn(s) + NO2
1-
(aq) → NH3(aq) + Zn(OH)4
2-
(aq)
c. N2H2(aq) + Cu(OH)2(s) → N2(g) + Cu(s)
d. Mn2+
(aq) + MnO4
1-
(aq) → MnO2(s)
e. Cl2(g) → ClO3
1-
(aq) + Cl1-
(aq)
3. Sketch the voltaic cell for each of the following RedOx reactions. Label the following: anode,
cathode, the half reaction at each electrode, electron flow, and ion flow.
a. 2Ag1+
(aq) + Pb(s) → 2Ag(s) + Pb2+
(aq)
b. 2ClO2(g) + 2I1-
(aq) → 2ClO2
1-
(aq) + I2(s)
c. O2(g) + 4H1+
(aq) 2Zn(s) → 2H2O(l) + 2Zn2+
(aq)
4. Determine the standard cell potential for each of the electrochemical cells and problem #3.
5. A voltaic cell containing a standard Cd2+/Cd electrode and a standard Au3+/Au electrode is
constructed and the circuit is closed. Without looking at a table of standard reduction potentials
diagram and describe the cell from the following experimental observations.
 Metallic gold plates out on one electrode and the gold ion concentration around that electrode
decreases.
 The mass of the cadmium electrode decreases, and the cadmium ion concentration increases
around the same electrode.
6. Repeat problem #5 for a voltaic cell containing standard Fe2+/Fe3+ and Pd2+/Pd electrode. The
following observations were made:
 The mass of the Pd electrode increases and the Pd2+ concentration decreases around that
electrode.
 The Fe2+ concentration decreases in the other electrode solution.
7. Calculate the standard cell potential for each of the electrochemical cells in problems 5 and 6.
8. Use shorthand notation to represent each of the electrochemical cells in problems 5 and 6.
9. Give the shorthand notation for electrochemical cells in which the following overall reactions occur
when the current flows. Calculate E°cell and ΔG°rxn.
a. Cr(s) + Cl2(g)⇄ CrCl2(aq) (Think!!)
b. Pb(s) + PbO2(s) + 2SO4
2-
(aq) + 4H+⇄ 2PbSO4(s) + 2H2O(l)
10. Calculate EC, EA, Ecell for each of the following cells:
a. Pt|Fe3+(aq,0.010M), Fe2+(aq,0.50M)||KCl(sat’d)|Hg2Cl2(s)|Hg(l)|Pt
b. Pt|O2(g,0.20atm)|HCl(aq,0.10M)||FeCl2(aq,0.10M|Fe
11. Based on E° values, what is the strongest reducing and oxidizing agent in each of the following
groups. Briefly explain your reasoning.
a. Strongest Reducing Agent: Ag(s), Ag+
(aq), Fe2+
(aq), Fe3+
(aq), Co2+
(aq), Co3+
(aq)
b. Strongest Oxidizing Agent: Cl2(g), Cl-
(aq), MnO4
–
(1M H+
), Mn2+(1M H+
), O2(1M H+
)
2
12. Use E° values to calculate K’s for the following reactions
a. Ksp for Hg2Cl2(s)
b. Kw for the autoionization of H2O
13. From the following shorthand notation, determine the reduction and oxidation half reactions and
then the overall reaction in the cell. Then determine Ecell and ΔG and if the reaction is spontaneous.
a. Sn|Sn2+(aq, 0.50M)||NO(g, 0.15atm)|NO3
1-
(aq, 0.035M)|Pt
b. Pt|H2(g,1atm)|Na+
,OH-
(aq,0.1M)||Na+
,OH-
(aq,0.1M)|O2(g,0.2atm)|Pt
14. Given the following data for the following half-reactions and E° (V vs. NHE):
Cu2+
+ 2e-⇄ Cu E°=0.340V
Cu2+
+ I-
+ e-⇄CuI E°=0.86V
O2 + 4H+
+ 4e-⇄ 2H2O E°=1.229V
H2O2 + 2H+
+ 2e-⇄ 2H2O E°=1.763V
Devise a thermodynamically sound basis for determining the standard potentials, E°, for new halfreactions by taking combinations of other half-reactions at 25°C for the following reactions.
a. CuI + e-⇄ Cu + Ib. O2 + 2H+
+ 2e-⇄ H2O2
15. The cell potential for this electrochemical cell depends on the pH of the solution in the anode halfcell. What is the pH of the solution of the Ecell is found to be 355mV?
Pt|H2(g, 1atm|H1+(aq, ??M)||Cu2+(aq, 1.0M)|Cu
16. What is the cell potential for each of the following reactions under the specified conditions at 25°C?
a. Zn(s) + 2H1+(aq, 0.001M) → Zn2+(aq, 3.0M) + H2(g, 5.0atm)
b. Cu(s) + 2Ag1+(aq, 1.0×10-6M) → Cu2+(aq, 0.050M) + 2Ag(s)
c. Sn4+(aq, 0.050M) + 2Fe2+(aq, 0.10M) → Sn2+(aq, 0.10M) + 2Fe3+(aq, 0.15M)
17. Determine ΔG and K for each of the reactions in problem 16 under the given conditions.
18. Given the following E° values at 25°C, calculate Ksp for cadmium sulfide, CdS.
Cd2+
(aq) + 2e- → Cd(s) E° = -0.403V
CdS(s) + 2e- → Cd(s) + S2-
(aq) E° = -1.21V
19. Determine ΔG° for the process in problem 18:
CdS(s) ⇄ Cd2+
(aq) + S2-
(aq)
20. The Ksp at 298K for iron(II) fluoride is 2.4×10-6
.
a. Write a half reaction that gives the likely products of the two-electron reduction of FeF2(s) in
water.
b. Use the Ksp value and the standard reduction potential of Fe2+
(aq) to calculate the standard
reduction potential for the half-reaction in part a. (Hint: Using Hess’s law chemical reactions can
be added together to get the desired reaction allowing the determination of thermodynamic
state functions.)
Fe2+
(aq) +2e- → Fe(s) E°=-0.440V
F
–
(aq) + e- → F2-
(aq) E°=-4.884V