Advanced Topic 600 of 1102 Acids, Bases & Electrochemistry
Pourbaix Diagram
Plots stable species of an element against pH and potential.
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In-depth explanation of Pourbaix Diagram
A Pourbaix diagram maps the stable chemical species of an element in water as a function of pH and electrode potential, dividing the plot into regions of immunity, corrosion and passivation. It is constructed from the Nernst equation and solubility data for all the relevant species. Lines on the diagram mark equilibria between species, and the boundaries show where one form becomes thermodynamically stable. It is used to predict whether a metal corrodes, forms a protective oxide or is immune under given conditions. The diagram is a key tool in corrosion engineering.
Going deeper: Pourbaix Diagram
Key ideas: A plot of electrode potential E (vertical) against pH (horizontal) showing regions of stability for a metal, its ions and oxides or hydroxides. Lines are drawn from the Nernst equation: vertical lines for pH-only equilibria, horizontal for redox only, sloped (-0.0592 m/n V per pH unit) when H+ is involved. Water stability lies between the O2 and H2 lines.
Common mistakes and connections: Mistakes: reading it as a rate guide (it shows thermodynamics only, not kinetics) and ignoring that diagrams assume a fixed ion concentration, often 1e-6 M. Regions: immunity, corrosion, passivation. Use it to select pH and potential for protection, such as Fe at high pH becoming passive.
Visualization of Pourbaix Diagram
The Pourbaix diagram of water: between the O2 and H2 lines water is stable, and both boundaries slide down by 59 mV per pH unit. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Iron is immune at low potential, but at moderate pH and potential it corrodes, as the Pourbaix diagram for iron shows.
Frequently asked questions about Pourbaix Diagram
What is Pourbaix Diagram?
Plots stable species of an element against pH and potential.
Is Pourbaix Diagram a beginner, intermediate or advanced topic?
Pourbaix Diagram is a advanced topic in Acids, Bases & Electrochemistry. It builds on beginner and intermediate topics, so review those first if needed.
What should I learn before Pourbaix Diagram?
Study these earlier topics in Acids, Bases & Electrochemistry first: Ionic Strength, Activity and Activity Coefficients, Overpotential.
What comes after Pourbaix Diagram?
The next topics in Acids, Bases & Electrochemistry are Latimer and Frost Diagrams and Ion-Selective Electrodes.
Can I practise Pourbaix Diagram with quizzes?
Yes. The interactive lesson includes a self-check question on Pourbaix Diagram, and the Acids, Bases & Electrochemistry quiz draws on every topic in this area.
Where Pourbaix Diagram fits in Acids, Bases & Electrochemistry
Pourbaix Diagram is topic 90 of 105 in Acids, Bases & Electrochemistry.