Source: http://www2.ucdsb.on.ca/tiss/stretton/chem2/ElectroEx4.html
Cell Potentials and Reduction Potentials
1. Given the following:
Fe2+ + 2 e- → Fe Eo = -0.40 volt
Ni2+ + 2 e- → Ni Eo = -0.25 volt
Fe3+ + 3 e- → Fe Eo = -0.40 volt
Fe3+ + e- → Fe2+ Eo = +0.77 volt
Br2 + 2 e- → 2 Br- Eo = +1.09 volt
Which of the substances listed below is the strongest oxidizing agent?
a) Fe
b) Fe2+
c) Fe3+
d) Br2
e) Br2. Given the following:
Fe2+ + 2 e- → Fe Eo = -0.40 volt
Ni2+ + 2 e- → Ni Eo = -0.25 volt
Fe3+ + 3 e- → Fe Eo = -0.40 volt
Fe3+ + e- → Fe2+ Eo = +0.77 volt
Br2 + 2 e- → 2 Br- Eo = +1.09 volt
Which of the following reactions is not spontaneous under standard
conditions?
a) Fe2+ + Ni → Fe + Ni2+
b) 2 Fe3+ + 3 Ni → 2 Fe + 3 Ni2+
c) 2 Fe3+ + Ni → 2 Fe2+ + Ni2+
d) 2 Fe3+ + Fe → 3 Fe2+
e) 2 Fe + 3 Br2 → 2 Fe3+ + 6 Br3. Given the following half cell reactions:
Cl2(g) + 2 e- → 2 Cl-(aq) Eo = +1.36 V
Fe3+(aq) + e- → Fe2+(aq) Eo = +0.77 V
Which one of the following reactions may occur spontaneously?
a) Cl2(g) + 2 Fe2+(aq) → 2 Cl-(aq) + 2 Fe3+(aq)
b) Cl2(g) + 2 Fe3+(aq) → 2 Cl-(aq) + 2 Fe2+(aq)
c) 2 Cl-(aq) + 2 Fe3+(aq) → Cl2(g) + 2 Fe2+(aq)
d) 2 Cl- + 2 Fe2+(aq) → Cl2(g) + 2 Fe3+
4. What is the standard cell voltage for
Cd(s) + 2 Ag+(aq) → Cd2+(aq) + 2 Ag(s) ?
Ag+(aq) + e- → Ag(s) Eo = +0.799 V
Cd2+(aq) + 2 e- → Cd(s) Eo = -0.402 V
a) +0.397 V
b) +0.799 V
c) +1.000 V
d) +1.201 V
e) +2.000 V
5. What do the positive and negative signs of reduction potentials tell us?
Positive sign of reduction potential means the electrode reaction is
spontaneous and negative sign means non-spontaneous reaction.
6. What is cell potential? What are its units?
The cell potential is the difference between the cathode(RHE) potential and
the anode (LHE) potential
7. What would be the cell reaction and the standard cell potential of a galvanic
cell employing the following half-reactions?
Al3+(aq) + 3 e- → Al(s) EoAl3+ = -1.66 V
Cu2+(aq) + 2 e- → Cu(s) EoCu2+ = 0.34 V
Which half-cell would be the anode?
Cell reaction: 2Al + 3Cu2+ → 2Al3+ + 3Cu
Eocell= +0.34-(-1.66) = 2.0 V
The anode is the Al electrode
8. What is the overall cell reaction and the standard cell potential of a galvanic
cell employing the following half-reaction?
NiO2(s) + 2 H2O + 2 e- → Ni(OH)2(s) + 2 OH-(aq) EoNiO2 = 0.49 V
Fe(OH)2(s) + 2 e- → Fe(s) + 2 OH-(aq) EoFe(OH)2 = -0.88 V
These are the reactions in an Edison cell, a type of rechargeable storage
battery.
LHE: Fe(s) + 2 OH-(aq) → Fe(OH)2(s) + 2 e-
EoFe(OH)2 = -0.88 V
RHE: NiO2(s) + 2 H2O + 2 e- → Ni(OH)2(s) + 2 OH-(aq) EoNiO2 = 0.49 V
Cell reaction: Fe+ NiO2 +2H2O → Fe(OH)2(s) + Ni(OH)2(s)
Eocell = 0.49 -(-0.88) 1.37V
For more details see http://www.uniregensburg.de/Fakultaeten/nat_Fak_IV/Organische_Chemie/Didaktik/Keusch/chembox_edison-e.htm
9. Calculate the standard-state cell potentials Eocell for these reactions:
a) Cl2 + Ni(s) → Ni2+ + Clb) 2 Ce4+ + 2 I- → 2 Ce3+ + 5 I2
c) Sn4+ + Cd(s) → Sn2+ + Cd2+
d) Br2 + 2 Fe2+ → 2 Br- + 2 Fe3+
10. Calculate the potential (voltage) of a standard cell with these half-cell
reactions:
Ni(s) → Ni2+ + 2 e2 e- + Cl2(g) → 2 Cl-