AQA Electrode Potentials and Electrochemical Cells Lecture Notes

Half Cells

• Definition: One half of an electrochemical cell
• Construction:
  • Metal dipped in its ions or
  • Platinum electrode with aqueous ions
• Example: Iron electrode in Fe²⁺/Fe³⁺ solution
• Reaction: Involves equilibrium between Fe²⁺ + 2e⁻ ↔ Fe
• Use of Platinum: For ions with no solid form due to good conductivity and inertness

Electrochemical Cell

• Components:
  • Two half-cells joined with wire, voltmeter, and salt bridge
• Salt Bridge: Completes the circuit, allows ion flow, typically uses KNO₃

Electrode Potentials (E°)

• Purpose: Measure potential of half-cells and shows how easily it's oxidised to predict redox reactions
• Electrochemical Series:
  • Always written in 'reduced form' (flip the –ve)
  • More negative = Better reducing agent
  • More Positive = Better oxidising agent
• Standard Hydrogen Electrode (SHE):
  • Reference for measuring potentials
  • E° = 0.00V
  • Conditions: 298K, 100 kPa, 1 mol dm-3 H⁺

Identifying Redox Reactions

• Acronym: PRON
  • Positive: Reduced (RIG = gains electrons)
  • Negative: Oxidised (OIL = loses electrons)
• EMF = Electromotive Force
• Electrode Potential Calculation:
  • EMF = E° (reduced/right/+ve) - E° (oxidised/left/–ve)

Cell Notation

• Purpose: Simplifies cell setup depiction
• Notation Rules:
  • Most negative half-cell on the left
  • Solid line for state changes
  • Double line for salt bridge
  • Comma for ions in the same state

Predicting Reactions

• Use electrode potentials to determine reaction feasibility
• Positive E° cell value indicates a feasible reaction

Batteries

• Types: Rechargeable and non-rechargeable
• Example: Lithium-ion batteries
• Components:
  • Electrode A: Lithium cobalt oxide
  • Electrode B: Graphite
  • Electrolyte: Lithium salt in organic solvent

Fuel Cells

• Continuous Fuel Supply: Unlike batteries
• Example: Alkaline hydrogen-oxygen fuel cell
• Pros:
  • More efficient than internal combustion engines
  • Only byproduct is water
• Cons:
  • Hydrogen is flammable and expensive to store
  • Production often reliant on fossil fuels

Conclusion

• Emphasis on the acronym "No Problem" for remembering oxidation and reduction processes
• Resources available for further learning and revision.