Electrochemistry Lecture

Introduction

• Instructor: Ajay Jhumri
• Subject: Electrochemistry (Part of Physical Chemistry)
• Target: Cover three chapters in seven days, starting today.

Chapter Overview

• Electrochemistry is one of the most important and tough chapters in Physical Chemistry.
• Concepts need to be understood thoroughly, starting from the basics.
• The chapter is particularly significant for exams like JEE Mains, NEET, and EAMCET.
• Generally, expects 1-2 questions in exams.

Key Sections in Electrochemistry

1. Conductance
2. Cell (Galvanic, Electrolytic, etc.)
3. Electrolysis

Detailed Discussion

Conductance

• Definition: Measure of the rate at which electric charge flows through a solution.
• Symbol: C
• Formula: C ∝ 1/R, where R is resistance.
• Units: Siemens (S), where 1 S = 1/Ω (Ohm inverse or Ohm^-1).

Factors Affecting Conductance

1. Number of Ions: More ions lead to higher conductance; directly proportional to concentration for strong electrolytes and inversely for weak ones.
2. Nature and Size of Ions: Smaller ions generally have higher conductance due to higher mobility.
3. Charge on Ions: Conductance is inversely proportional to the charge on ions.
4. Temperature: Higher temperatures generally increase conductance.

Types of Electrolytes

• Strong Electrolytes: Dissociate fully in solution (e.g., NaCl, HCl), high λ (molar conductance).
• Weak Electrolytes: Partially dissociate (e.g., Acetic acid), low λ.

Specific Conductance (κ or κappa)

• Definition: Conductance of a solution of 1 cm³ volume between electrodes 1 cm apart.
• Units: Siemens per meter (S/m) or Siemens per centimeter (S/cm).
• Formula: κ = C × (L/A), where L is the distance between electrodes and A is the cross-sectional area of the electrode.

Molar Conductance (Λm)

• Definition: Conductance of all ions produced by one mole of electrolyte in solution.
• Units: S·cm²·mol⁻¹.
• Formula: Λm = (κ × 1000) / M, where M is molarity.

Equivalent Conductance (Λe)

• Definition: Conductance of a solution containing 1 gram equivalent of electrolyte.
• Formula: Λe = κ × (1000 / Normality), related to Λm by the factor of valency.

Relationships and Trends

• Strong Electrolytes: Λm increases slightly with dilution due to complete ionization.
• Weak Electrolytes: Λm increases significantly with dilution due to increased ionization.

Common Questions and Problems

1. Calculating conductance and specific conductance using the given values and relationships.
2. Relating molar conductance with concentration, typically involving formula manipulation.
3. Understanding and applying Kohlrausch's Law for weak electrolytes.
4. Determining the conductance ratio and its implications for ionic speeds and solution behavior.

Practical Implications and Experimental Setup

• Equipment: Conductivity meter, electrolytes, defined electrode setup.
• Key Considerations: Temperature control, accurate molarity calculations, maintaining clean electrodes.

Summary

• Focus Areas: Basics and conceptual clarity are crucial, especially for weak vs strong electrolytes and their respective behaviors in solutions.
• Exam Preparation: Understand key relationships, practice problem-solving extensively, and apply theoretical knowledge to practical scenarios.