Lecture on Redox Reactions in Galvanic Cells

Introduction

• Context: Lecture held in South Africa on a cold day.
• Topic: Redox reactions in galvanic cells.

Redox Reactions

• Redox is a compound word from "reduction" and "oxidation".
  • Reduction: Gain of electrons.
  • Oxidation: Loss of electrons.
• Redox reactions involve the transfer of electrons.

Structure of a Galvanic Cell

• Made of two beakers or containers.
• Contains electrodes (usually metals) and an electrolyte (soluble substance).
• Includes a voltmeter and wires.
• Salt Bridge: Contains a highly soluble salt with porous plugs (e.g., cotton wool).
  • Functions:
    • Neutralizes excess ions.
    • Completes the circuit.

Electrodes and Electrolytes

• Electrodes are the metals or materials that conduct electricity.
• Electrolyte: Must be a soluble solution.
• Use nitrates as electrolytes due to solubility (e.g., zinc nitrate for zinc electrode).

Concepts of Electrode Reactions

• Cathode: Electrode undergoing reduction (gains mass).
  • Mnemonic: Red Cat (reduction at the cathode).
• Anode: Electrode undergoing oxidation (loses mass).
  • Mnemonic: An Ox (oxidation at the anode).
• Energy Conversion: Chemical energy to electrical energy (in galvanic cells).
  • Reaction is spontaneous (happens naturally).

Agents in Redox Reactions

• Oxidizing Agent: Substance that undergoes reduction.
• Reducing Agent: Substance that undergoes oxidation.

Standard Reduction Potential

• Use a standard hydrogen electrode as a reference.
• Standard Conditions:
  • Temperature: 25°C
  • Concentration: 1 M
  • Pressure: 1 atm (if a gas is involved)
• Electrode potentials indicate preference for oxidation or reduction.

Example of a Galvanic Cell

• Zinc-Copper Cell: Common example.
  • Zinc undergoes oxidation; copper undergoes reduction.
  • Electrons move from anode to cathode.

Calculating Cell Potential

• Use the formula:
  • [ E_{cell} = E_{cathode} - E_{anode} ]
• Example: Zinc (-0.76V) and Copper (+0.34V)
  • [ E_{cell} = 0.34 - (-0.76) = 1.10V ]

Reaction Observations

• Zinc electrode corrodes (loses mass); copper electrode gains mass.
• Electrons flow from zinc to copper.

Standard Cell Notation

• Anode to cathode transition described using standard notations.
  • Example: Zn | Zn²⁺ || Cu²⁺ | Cu

Key Takeaways

• Understanding of electron flow and energy conversion in galvanic cells.
• Importance of salt bridges and standard conditions.
• Use standard reduction potential tables to predict reaction behavior.

Conclusion

• Encouragement to study and apply concepts for exams.