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2.10: Ladder Diagrams: Redox Equilibria

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JoVE Core
Analytical Chemistry

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Ladder Diagrams: Redox Equilibria
 
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2.10: Ladder Diagrams: Redox Equilibria

Ladder diagrams are useful tools for understanding redox equilibrium reactions, especially the effects of concentration changes on the electrochemical potential of the reaction. The vertical axis in the redox ladder diagrams represents the electrochemical potential, E. The area of predominance is demarcated using the Nernst equation.

Consider the Fe3+/Fe2+ half-reaction, which has a standard-state potential of +0.771 V. At potentials more positive than +0.771 V, Fe3+ predominates, whereas Fe2+ predominates at potentials more negative than +0.771 V. When the Fe3+/Fe2+ half-reaction is coupled with the Sn4+/Sn2+ reaction, the concentration of Fe3+ can be reduced by adding Sn2+ to excess. In this case, the potential of the resulting solution approaches +0.154 V down to +0.771 V, and Fe2+ and Sn4+ predominate.

To understand the interdependence between change in solution pH and electrochemical potential, consider the example of UO22+/U4+ half-reaction, whose electrochemical potential varies with the pH of the solution. As the pH of the solution decreases, the electrochemical potential increases, changing the dominant species from U4+ to UO22+.

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Keywords: Ladder Diagrams Redox Equilibrium Electrochemical Potential Nernst Equation Fe3+/Fe2+ Half-reaction Sn4+/Sn2+ Reaction UO22+/U4+ Half-reaction PH Dependence Dominant Species

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