Lecture Notes on Standard Reduction Potentials and Redox Reactions

Key Concepts

• Standard Reduction Potential: Measures the tendency of a chemical species to be reduced, expressed in volts. More positive values indicate a greater likelihood of reduction.
• Reduction and Oxidation:
  • Reduction involves the gain of electrons.
  • Oxidation involves the loss of electrons.

Standard Reduction Potentials

• Reduction half-reactions are shown with their potential values.
• The Standard Hydrogen Electrode (SHE) has a potential of 0 volts and serves as the reference.
• A more positive standard reduction potential value means the substance is more likely to be reduced.

Example Half-Reactions

• Silver Ion to Solid Silver
  • Reaction: Ag⁺ + e⁻ → Ag
  • Standard Reduction Potential: +0.80 volts
• Copper Ion to Solid Copper
  • Reaction: Cu²⁺ + 2e⁻ → Cu
  • Standard Reduction Potential: +0.34 volts
• Zinc Ion to Solid Zinc
  • Reaction: Zn²⁺ + 2e⁻ → Zn
  • Standard Reduction Potential: -0.76 volts

Comparing Reduction Potentials

• Copper vs. Zinc
  • Copper has a more positive potential than zinc, making it more likely to be reduced.
  • In a redox reaction involving copper and zinc, copper ions are reduced and zinc is oxidized.

Writing Redox Reactions

• Reduction Half-Reaction
  • Example: Cu²⁺ + 2e⁻ → Cu
  • Standard Reduction Potential: +0.34 volts
• Oxidation Half-Reaction
  • Starting with solid zinc, oxidation is reversed: Zn → Zn²⁺ + 2e⁻
  • Standard Oxidation Potential: +0.76 volts (sign changed from reduction potential)
• Overall Redox Reaction
  • Combine half-reactions: Cu²⁺ + Zn → Cu + Zn²⁺
  • Standard Cell Potential: +1.10 volts (sum of reduction and oxidation potentials)

Calculating Cell Potential

• Combine reduction and oxidation potentials to find the standard cell potential.
• Measured potential of a voltaic cell is +1.10 volts under standard conditions.

Oxidizing and Reducing Agents

• Zinc
  • Acts as a reducing agent because it loses electrons and facilitates the reduction of copper.
• Copper
  • Acts as an oxidizing agent because it gains electrons and facilitates the oxidation of zinc.

Trends in Reduction Potentials

• Oxidizing Agents
  • Greater tendency to be reduced as you move up the standard reduction potential table.
  • Copper is a stronger oxidizing agent than zinc.
• Reducing Agents
  • Greater tendency to be oxidized as you move down the table.
  • Zinc is a stronger reducing agent than copper.
  • Lithium has an even more negative potential, making it a stronger reducing agent than zinc.