Conductance In Electrolytic Solutions

1.0Introduction

Electrochemistry explores the interconversion of chemical energy and electrical energy. It examines how spontaneous chemical reactions generate electricity and how electrical energy drives non-spontaneous chemical reactions.

Electrochemistry is fundamentally based on redox reactions, where oxidation and reduction occur simultaneously. Electrochemical cells facilitate these transformations by converting chemical energy into electrical energy or using electrical energy to induce chemical changes.

2.0Types Of Electrochemical Cells

Electrochemical cells are classified into two main types:

1. Electrolytic Cells – These cells use electrical energy to drive non-spontaneous chemical reactions, converting electrical energy into chemical energy.
2. Galvanic (Voltaic) Cells – These cells generate electrical energy from spontaneous chemical reactions, converting chemical energy into electrical energy. Galvanic cells are further categorised into:

• Chemical Cells – Electrical energy is produced solely by chemical changes within the cell, without transferring matter. (Example: Batteries)
• Concentration Cells – Electrical energy is generated through physical changes involving the transfer of matter from one part of the cell to another. (Example: Standard Hydrogen Electrode)

Electrochemistry primarily focuses on three main aspects:

1. Electrolysis (Electrolytic Cells) – The process where electrical energy drives a non-spontaneous chemical reaction.
2. Galvanic (Voltaic) Cells – Systems where spontaneous chemical reactions produce electrical energy.
3. Electrolytic Conduction – The study of how electric current flows through an electrolyte via the movement of ions.

3.0Conductance Of Electrolytic Solutions

Conductors are materials that allow electricity to pass through them, while insulators do not conduct electricity. Conductors are classified into two main types:

1. Electronic Conductors (Metallic Conductors)

These conduct electricity without undergoing any decomposition. Conductance is due to the flow of electrons rather than ions.

Examples: Metals, graphite, and certain minerals.

Properties:

• Conductance depends on the structure, density, and number of valence electrons per atom.
• An increase in temperature decreases conductivity because vibrating metal ions (kernels) hinder the flow of electrons.
• Resistance arises due to the vibrations of metal kernels.

2. Electrolytic Conductors

These conduct electricity through the movement of ions rather than electrons. When an electric current passes through, electrolytic decomposition occurs.

Examples: Solutions of acids, bases, and salts in water.

Properties:

• Conductance increases with temperature due to increased ion dissociation and reduced interionic attraction.
• Resistance depends on factors such as interionic attractions and the viscosity of the solvent.

4.0Specific Conductivity, Equivalent Conductivity, and Molar Conductivity

1. Specific Conductivity (κ)

• Also known as conductivity, it is the conductance (G) of a one-centimetre cubic solution of an electrolyte.
• Denoted by κ (kappa).
• It represents the conductance of a solution with a length (l) of one centimetre and a cross-sectional area (a) of one square centimetre.
• Specific conductivity is the reciprocal of resistivity.
• Formula: $k=\frac{l\times G}{a}$
• Unit: Siemens per meter (S m⁻¹) or ohm⁻¹ cm⁻¹.

2. Equivalent Conductivity (Λeq)

• The conductance of all ions produced from one gram equivalent of an electrolyte dissolved in V cm³ of solution.
• Formula: $\Lambda eq=k\times \frac{1000}{C_{eq}}$, where $C_{eq}$ is the normality (gram equivalent per 
• $\Lambda eq=k\times \frac{1000}{Normality}$
• Unit: S m² eq⁻¹ or S cm² eq⁻¹.

3. Molar Conductivity (Λ_m )

• The conductance of all ions produced from one mole of an electrolyte dissolved in V cm³ of solution.
• Formula:Λ_m = κ×V, where V is the volume of the solution containing one mole of electrolyte.
• Unit: S m² mol⁻¹.

5.0Strong Electrolytes And Weak Electrolytes

Strong Electrolytes

• Electrolytes that completely dissociate in aqueous solutions or a molten state.
• Examples: HCl, H₂SO₄, HNO₃, NaCl, KCl.

Weak Electrolytes

• Electrolytes, with a low degree of dissociation, conduct electricity to a lesser extent.
• Examples: NH₄OH, Ca(OH)₂, CH₃COOH.