Physical Chemistry Experiment - Amperometry

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Physical Chemistry Experiment:

Amperometry

Introduction:

A general redox reaction Ox +né ⇋Red has three different ways of mass transport, diffusion, migration and convection.

The first one is the motion of the species in a gradient which appears when there is a change of concentration at the electrode. The concentrations of the oxidant and the reducer are functions of the distance of the electrode due to the reaction and a layer of thickness up to 10-2 can appear. Because of this the concentration of the oxidant at the electrode is weaker than in the solution. The diffusion of the oxidant from the solution to the electrode takes place and can be describes thanks to the Fick equation.

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Where  is the molecular flow by unit of surface and time [mol m-2 s-1],  is the diffusion coefficient [m2 s-1],, x is the distance of the oxidant from the electrode [m] and  is the concentration [M].[pic 3][pic 4][pic 5]

Then the migration is the motion of the charged species in a potential field. This describes the transport of the charges through the electrolyte. The electrons flow in the conductor and the flow of the ions in the solution between the electrodes have to be equal, and the migration flow is given by: