Question

Freundlich isotherm becomes Nernst isotherm when n is

• A. 0.2
• B. 0.5
• C. 0.8
• D. 1.0

Hint:

The Freundlich isotherm becomes the Nernst (linear) isotherm when the Freundlich constant 'n' equals 1. This signifies a constant distribution of the adsorbate between the solid and solution phases.

Answer 1

The Correct Option is D

Step 1: Understanding Adsorption Isotherms: Adsorption isotherms describe the relationship between the amount of a substance adsorbed onto a surface (e.g., dye onto a fiber) and the concentration of the substance in the surrounding solution at equilibrium.
Step 2: Freundlich Isotherm: The Freundlich isotherm is an empirical equation: \[ x/m = K C^{1/n} \] where: \( x \) is the mass of adsorbate (e.g., dye) adsorbed. \( m \) is the mass of adsorbent (e.g., fiber). \( C \) is the equilibrium concentration of the adsorbate in solution. \( K \) and \( n \) are constants that depend on the system (dye, fiber, temperature). \(n\) is greater than 1. The Freundlich isotherm typically applies to heterogeneous surfaces and suggests multilayer adsorption.
Step 3: Nernst Isotherm (Distribution Law): The Nernst isotherm (also known as the linear isotherm or distribution law) describes a simple linear relationship: \[ x/m = KC \] where K is a constant (distribution coefficient). This implies a constant ratio of adsorbate concentration on the solid phase to that in the solution phase.
Step 4: Freundlich Becoming Nernst: The Freundlich equation becomes the Nernst equation when the exponent \( 1/n \) equals 1. This happens when \( n = 1 \).