Electrochemistry Worksheet #3
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)  Br-
 

2.  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 Br-
 

3. 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?
 
6. What is emf?  What are its units?
 
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?
 

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.
 

9. Calculate the standard-state cell potentials Eocell for these reactions:
a) Cl2 + Ni(s) ? Ni2+ + Cl-

b) 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 e-
         2 e- + Cl2(g) -----> 2 Cl-