Elector Chemical Cells Practice Problems

Wkst 3: Electrochemical Cells – Practice Problems

1. Write half-cell reactions and give standard reduction potentials for these reduction reactions. (use table)

a) Cu+ è Cu

b) Cl2 è 2Cl-

c) Cu2+ è Cu

d) Ba2+ è Ba

e) Ag+ è Ag

2. Determine which metal will be the anode, and E°cell for the following sets of half-reactions:

a) Al3+ + 3e- ===> Al E° =-1.66 V

Au3+ + 3e- ===> Au E° =+1.50 V

b) Li+ + e- ===> Li E° = -3.05 V

Ag+ + e- ===> Ag E° = +0.80 V

c) Mg2+ +2e- ===> Mg E° = -2.37 V

Fe3+ + 3e- ===> Fe E° = -0.036 V

3. Two half-cells, one containing Fe2+ and Fe and the other containing Ag+ and Ag, are connnected to form a voltaic cell. Use a Standard Reduction Potential table to determine the direction of spontaneous reaction and the value for E°cell. Diagram the cell and label its parts. Give equations for the half reactions.

4. Use a Standard Reduction Potential table to determine the E°cell value for the spontaneous reaction of each pair of half-cells listed below:

a) Ag ===> Ag+ + 1e-; Fe2+ + 2e- ===> Fe

b) Mg ===> Mg2+ + 2e-; Sn2+ + 2e- ===> Sn

c) Li ===> Li+ + 1e-; Mn2+ + 2e- ===> Mn

d) Cr ===> Cr3+ + 3e-; Hg2+ + 2e- ===> Hg

e) Ni ===> Ni2+ + 2e-; Cu2+ + 2e- ===> Cu

5. Two half cells, one containing Ca2+ and Ca and the other containing Ag+ and Ag, are connected to form a voltaic cell. Use a Standard Reduction Potential table to determine the direction of spontaneous reaction and the value for E° cell. Diagram the cell and label its parts. Give equations for the half reactions.

6. Explain why a rechargeable battery can be considered a combination voltaic-electrolytic cell.

7. A voltaic cell is composed of the following half-cells:

Ca2+ + 2e- è Ca E° = -2.87 V

Fe3+ + e- è Fe2+ E° = +0.77 V

Write the reaction that takes place at the anode (oxidation) and the reaction that takes place at the cathode (reduction). Calculate the standard cell potential (E° cell).

8. What is the standard cell potential for a voltaic cell composed of the following half-cells:

Cu2+ + 2e- è Cu E° = +0.34 V

Ag+ + e- è Ag E° = +0.80 V

Write the reaction that occurs at the anode (oxidation) and the cell reaction that occurs at the cathode (reduction).

9. Is the following redox reaction spontaneous as written? (Hint: write oxidation and reduction half-reactions; look up the standard reduction potentials, and find E° cell; if E° is positive, the reaction is spontaneous!)

2Ag+ + Ni è 2Ag + Ni2+

10. Decide if the following redox reaction is spontaneous as written: (see hint in #9)

Cr3+ + Al è Cr + Al3+