Dissemination of IT for the Promotion of Materials Science (DoITPoMS)

DoITPoMS Teaching & Learning Packages The Nernst Equation and Pourbaix Diagrams Example 1
The Nernst Equation and Pourbaix Diagrams AimsBefore you startIntroductionBackgroundThe Nernst equationConstruction of a Pourbaix DiagramAnatomy of a Pourbaix DiagramExamples of a Pourbaix DiagramConstructing a 3D Pourbaix DiagramSummaryQuestionsGoing further
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Example 1

Find the electrochemical reaction for an equilibrium between Zn and Zn(OH)42–

1. Write reduced species on right

 Zn(OH) 4 2–  →  Zn

2. Balance zinc atoms

 Zn(OH) 4 2–  →  Zn

3. Balance oxygen atoms with water

 Zn(OH) 4 2–  →  Zn +   4 H2O

4. Balance hydrogen atoms with hydrogen ions

 Zn(OH) 4 2–  +  4 H+ →  Zn   +   4 H2O

5. Balance charge with electrons

  Zn(OH) 4 2– + 4 H+ + 2 e-  →   Zn  + 4 H2O

Check: Each side of the equation has: One Zn, four O, four H and zero residual charge – so it is balanced.

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