VTU E-Shikshana Program: Electrochemistry Lecture

Recap of Previous Lecture

• Introduction to Electrochemistry
• Concepts covered:
  • Free Energy
  • E cell (Electromotive Force of the cell)
  • E naught cell (Standard EMF)
  • Galvanic Cells
  • Differences between Electrolytic and Galvanic Cells
  • Derived Nernst Equation for Single Electrode Potential

Today's Focus: Nernst Equation Numerical Problems

Nernst Equation

• For single electrode potential:
  • E = E naught + (0.0591/N) log Mn+
• For the cell:
  • E cell = E0 cell - (2.303 RT/NF) log [(C^C D^D)/(A^A B^B)]
  • Products in numerator and reactants in denominator.

Problem Solving Using Nernst Equation

Problem 1: Standard Cadmium Copper Cell

• Representation: Cd | Cd²⁺ || Cu²⁺ | Cu
• Anodic Reaction: Cd → Cd²⁺ + 2e⁻
• Cathodic Reaction: Cu²⁺ + 2e⁻ → Cu
• Net Cell Reaction: Cd + Cu²⁺ → Cd²⁺ + Cu
• Standard EMF Calculation:
  • E0 cell = E0 cathode - E0 anode = 0.34 V - (-0.4 V) = 0.74 V

Problem 2: Nickel Silver (NiAg) Cell

• Representation: Ni | Ni²⁺ || Ag⁺ | Ag
• Anodic Reaction: Ni → Ni²⁺ + 2e⁻
• Cathodic Reaction: Ag⁺ + e⁻ → Ag
• Net Cell Reaction: Ni + 2Ag⁺ → Ni²⁺ + 2Ag
• Standard EMF Calculation:
  • E0 cell = E0 Ag - E0 Ni = 0.8 V - (-0.25 V) = 1.05 V

Problem 3: Fe | Fe²⁺ || Ag⁺ | Ag

• Cell Reaction: Fe + 2Ag⁺ → Fe²⁺ + 2Ag
• E0 cell Calculation:
  • E0 cell = 0.8 V - (-0.44 V) = 1.24 V
• EMF Calculation at 298K using given concentrations:
  • E = E0 - (0.0591/2) log (0.01/0.1²)

Problem 4: Zn | ZnSO₄ || AgNO₃ | Ag (23°C)

• Standard EMF Calculation:
  • E0 cell = 0.8 V - (-0.75 V) = 1.55 V
• EMF Calculation:
  • E = 1.55 - (0.0674)

Problem 5: Mg | Mg²⁺ || Ag⁺ | Ag

• Cell Reaction: Mg + 2Ag⁺ → Mg²⁺ + 2Ag
• Standard EMF Calculation:
  • E0 cell = 0.8 V - (-2.37 V) = 3.17 V
• EMF Calculation:
  • E = 3.17 - (calculated value)

Further Problems

• Calculation of half-cell potential, EMF of the cell using various concentrations and conditions.
• Practice problems involve applying Nernst equation with different cell setups and conditions to calculate potential differences and concentrations.

---

These notes cover the key concepts and examples from the lecture on solving electrochemistry problems using Nernst Equation, focusing on the calculation of EMF and standard cell potentials for different electrochemical cells.