Electrochemistry Lecture Notes

Introduction

• Chapter: Electrochemistry (Class 12 Chemistry, Chapter 2)
• Importance: Significant for competitive exams and boards
• Common Pitfall: Students often jump directly to numericals without understanding concepts leading to difficulties
• Main Concepts: Daniel Cell, Electrochemical Cells, Reduction Potential, Nernst Equation, Electrolysis, Faraday’s Laws, and Electrical Conductance

Key Concepts

Electrochemistry

• Combination of electric current and chemical reactions
• Focus: Mechanism of generating electric current from chemical reactions and vice versa

Electrochemical Cells

• Also Known As: Galvanic or Voltaic Cells
• Function: Convert chemical reactions into electric current
• Example: Daniel Cell
• Redox Reactions: Simultaneous oxidation and reduction occurring

Experiment Explanation

• Setup: Zinc rod in CuSO₄ (Copper Sulphate) solution
• Observations:
  • Zinc rod decreases in weight (Zn oxidizes)
  • Solution fades from blue (reduction of Cu²⁺ to Cu)
  • Red precipitate forms
  • Temperature rise observed
• Interpretation: Direct Redox reaction occurring, Zinc undergoes oxidation (Zn → Zn²⁺ + 2e⁻), Copper undergoes reduction (Cu²⁺ + 2e⁻ → Cu)
• Energy: Chemical energy converting to heat, not usable as electrical energy directly

Daniel Cell Setup

• Components: Zinc rod in ZnSO₄ solution (oxidation), Copper rod in CuSO₄ solution (reduction)
• Reactions:
  • Oxidation at zinc rod: Zn → Zn²⁺ + 2e⁻
  • Reduction at copper rod: Cu²⁺ + 2e⁻ → Cu
• Electrodes:
  • Anode: Negative (Oxidation, Zn)
  • Cathode: Positive (Reduction, Cu)
• Current Flow: From positive to negative (external circuit)

Problems in Electrochemical Cell

• Charge Imbalance:
  • Solutions become charged over time (Zn²⁺ increase in anode chamber, SO₄²⁻ increase in cathode chamber)
  • Results in electrostatic forces preventing further electron flow

Solution: Salt Bridge

• Function: Maintains charge neutrality and allows continuous electric current
• Components: Inverted U-tube containing inert electrolyte like KCl, K₂SO₄, KNO₃, NH₄Cl
• Mechanism: Allows ions to move and neutralize charge build-up
• **Functions: **
  1. Maintains electrical neutrality of electrolytes
  2. Completes the circuit
  3. Minimizes liquid-liquid junction potential

Conditions for Salt Bridge Electrolyte

• Inert Nature: Must not react with the ions of the half cells
• Good Ionic Mobility: Must allow ions to move easily

Cell Representation and Reaction

• Cell Representation:
  • Left side: Oxidation half-cell (Anode)
  • Right side: Reduction half-cell (Cathode)
  • Example: Zn | Zn²⁺ (1M) || Cu²⁺ (1M) | Cu
• Cell Reaction: Electrons in the half-reactions must cancel out
  • Example: Zn + Cu²⁺ → Zn²⁺ + Cu

Examples and Sample Problems

1. Write Cell Reaction for Ni | Ni²⁺ (0.1M) || Ag⁺ (1M) | Ag

• Oxidation Half-Cell: Ni → Ni²⁺ + 2e⁻
• Reduction Half-Cell: 2Ag⁺ + 2e⁻ → 2Ag
• Cell Reaction: Ni + 2Ag⁺ → Ni²⁺ + 2Ag

2. Write Cell Reaction for Cr | Cr³⁺ (1M) || Pb²⁺ (1M) | Pb

• Determine balancing if needed for electrons

Upcoming Topics

• Next Lecture: Reduction potential, electrode potential, Nernst Equation, understanding cell potential across different conditions
• Applications: Cell potential in different battery configurations