Question

The Pourbaix diagram represents the metal's:

• A. Mechanical strength vs. temperature
• B. Potential-pH stability regions
• C. Electrical conductivity vs strength
• D. Magnetic domain formation

Hint:

Horizontal lines on a Pourbaix diagram represent pure electron-transfer reactions (independent of pH), while vertical lines represent pure acid-base reactions (independent of potential).

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks what physical or electrochemical variables are mapped on a Pourbaix diagram.

Step 2: Key Formula or Approach:
Pourbaix diagrams are calculated based on the Nernst equation for electrochemical reactions:
\[ E = E^\circ - \frac{RT}{nF} \ln Q \]
For reactions involving hydrogen ions (\( \text{H}^+ \)), the potential \( E \) becomes a linear function of pH, since:
\[ \text{pH} = -\log[\text{H}^+] \]

Step 3: Detailed Explanation:

• Variables Mapped: A Pourbaix diagram is a thermodynamic plot of electrode potential (\( E \), usually relative to the Standard Hydrogen Electrode on the y-axis) versus pH (on the x-axis) for a metal-water system.

• Stability Regions: The diagram is divided into major thermodynamic regions:
1.

Immunity: The metal itself is thermodynamically stable and will not corrode.
2.

Corrosion: Soluble metal ions are stable, meaning the metal will actively dissolve.
3.

Passivity: Insoluble oxides or hydroxides form a protective surface film, limiting further corrosion.

• Other Options: The diagram does not contain any mechanical (Option A), electrical (Option C), or magnetic (Option D) properties.


Step 4: Final Answer:
Therefore, the Pourbaix diagram represents the Potential-pH stability regions of a metal, corresponding to Option (B).