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Ethanol Agar Diffusion Lab

Quantitative Ethanol Diffusion in Agar Gel Using Raman Spectroscopy

Learning Objectives:

  1. Determine the benefits of Raman and IR spectroscopies

  2. Analyze similar compounds with vibrational spectroscopies

 

Introduction:

There are two prominent demonstrations used to show diffusion.  First, cotton balls are wet with HCl and NH3 and stuck into the ends of a long glass tube. As these gasses diffuse through the tube they meet and combine to form visible NH4Cl.1 This lab primarily demonstrates the effect of mass on diffusion as the location of the NH4Cl is based on the ratio of the molecular masses of the reactants. A second lab measures the diffusion of a colored solution or dye by measuring distance relative to time. Although this method measures two of the key components of individual diffusion, it fails to measure concentration. Some labs adjust for this by using colorimeters.2

 

In this lab, all three variables related to diffusion will be measured in order to approximate the diffusion constant of ethanol in a water-based gel using Raman spectroscopy.