Lecture Notes: Predicting Oxidation of Metals by Lead (II) and Calculating Standard Cell Potentials

Objectives

• Predict whether lead (Pb2+) can oxidize solid aluminum (Al) or solid copper (Cu) under standard state conditions.
• Calculate standard cell potentials (E⁰) for each reaction at 25°C.

Key Concepts

• Standard Reduction Potential Table: A table listing half-reactions as reductions and their potentials in volts.
• Oxidizing Agent: A substance that gains electrons and is reduced.
• Diagonal Rule: An oxidizing agent can oxidize any reducing agent that lies below it on the standard reduction potential table.

Predictions

1. Lead (Pb2+) and Aluminum (Al)
   • Position: Aluminum is below lead (Pb2+) on the table.
   • Prediction: Yes, Pb2+ can oxidize Al (diagonal from Pb2+ to Al).
2. Lead (Pb2+) and Copper (Cu)
   • Position: Copper is above lead (Pb2+) on the table.
   • Prediction: No, Pb2+ cannot oxidize Cu.

Calculating Standard Cell Potentials

Pb2+ Oxidizing Al

• Reduction Half-Reaction: Pb2+ + 2e- → Pb
  • Standard Reduction Potential: -0.13 V
• Oxidation Half-Reaction: Al → Al3+ + 3e-
  • Reverse and change sign: Standard Oxidation Potential: +1.66 V
• Balancing Electrons:
  • Multiply Pb2+ half-reaction by 3 (6 electrons)
  • Multiply Al half-reaction by 2 (6 electrons)
• Overall Reaction: 3Pb2+ + 2Al → 3Pb + 2Al3+
• Standard Cell Potential Calculation:
  • E⁰ = -0.13 V + 1.66 V = +1.53 V
  • Result: Positive E⁰ indicates a spontaneous reaction.

Pb2+ and Cu

• Reduction Half-Reaction: Pb2+ + 2e- → Pb
  • Standard Reduction Potential: -0.13 V
• Oxidation Half-Reaction: Cu → Cu2+ + 2e-
  • Reverse and change sign: Standard Oxidation Potential: -0.34 V
• Overall Reaction: Pb2+ + Cu → Pb + Cu2+
• Standard Cell Potential Calculation:
  • E⁰ = -0.13 V + (-0.34 V) = -0.47 V
  • Result: Negative E⁰ indicates a non-spontaneous reaction.

Conclusions

• Aluminum vs. Copper
  • Aluminum is more easily oxidized than copper (more negative standard reduction potential).
  • Aluminum is more active than copper.
• The activity series can be explained through standard reduction potentials, reinforcing concepts from general chemistry.

Summary

• Lead (Pb2+) can oxidize aluminum but not copper under standard state conditions.
• Calculated standard cell potentials confirmed predictions: +1.53 V for Pb2+ and Al (spontaneous), -0.47 V for Pb2+ and Cu (non-spontaneous).
• Aluminum is more active than copper, aligning with the activity series.