Lecture Notes: Redox Equilibria - Standard Electrode Potentials

Introduction

• Topic: Redox Equilibria, focusing on Standard Electrode Potentials.
• Relevant for the IE2 course for Edexcel Chemistry.

Key Concepts

• Oxidation & Reduction (Redox Reactions):
  • Oxidation: Loss of electrons, increase in oxidation number.
  • Reduction: Gain of electrons, decrease in oxidation number.
  • Remember: OIL RIG (Oxidation Is Loss, Reduction Is Gain).
  • Redox reactions involve a paired oxidation and reduction reaction.

Redox Equilibria

• Dynamic Equilibrium:

  • Forward and reverse reactions occur at the same rate.
  • Involves reactions between metals and their solutions.

• Electrode Potentials:

  • Measure the tendency of a metal to lose or gain electrons.
  • Use voltmeters to determine potential difference.
  • Absolute Potential Difference: Difficult to measure directly.

Standard Hydrogen Electrode

• Reference Electrode:
  • Used to measure electrode potentials of other metals.
  • Consists of hydrogen gas (100 kPa), platinum electrode, and hydrochloric acid (1 mol/dm³).
  • Conditions: 298 K temperature.
• Standard Electrode Potential (E°):
  • Measured relative to the standard hydrogen electrode.
  • E° values: positive or negative indicating the position of equilibrium.

Measuring Electrode Potentials

• Half Cells:

  • Consist of a metal and its ion in solution.
  • Combined with standard hydrogen electrode to form an electrochemical cell.
  • Require a salt bridge and high resistance voltmeter.

• Electromotive Force (EMF):

  • Measured when no electrons are flowing.
  • Provides the standard electrode potential for a half cell.

Factors Affecting Electrode Potential

• Position of Equilibrium:
  • More negative E°: Equilibrium lies to the left, metal loses electrons easily.
  • More positive E°: Equilibrium lies to the right.

Electrochemical Series

• Ordering of Metals:
  • Based on their standard electrode potentials.
  • Most Negative: Strong reducing agents.
  • Most Positive: Strong oxidizing agents.

Applications

• Determining Reactivity:
  • Helps predict the feasibility of redox reactions.
  • Useful in understanding oxidizing and reducing power.

Exam Preparation

• Diagram Labeling:

  • Be familiar with labeling diagrams of the standard hydrogen electrode.
  • Know the conditions: pressure, temperature, concentration.

• Past Paper Questions:

  • Practice standard electrode potential questions.
  • Understand the role of platinum and porous surfaces in electrodes.

Conclusion

• Recap on measuring standard electrode potentials.
• Upcoming topics to include thermodynamic feasibility and electrochemical cells.

Further Reading

• Review the electrochemical series in your data book for more examples.
• Assess the impact of electrode potentials on industrial applications of electrochemistry.