Introduction
Standard electrode potentials help predict the direction of redox reactions and compare the strengths of oxidizing and reducing agents. These values are measured relative to a common reference electrode under standard conditions.
🔹 1. What is an Electrode Potential?
Electrode potential is the voltage produced when a metal (or other electrode) is in contact with a solution of its ions.
🔹 2. Standard Electrode Potential (E°)
It is the potential of a half-cell under standard conditions (1 mol/dm³, 1 atm, 25°C) relative to the Standard Hydrogen Electrode (SHE).
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SHE is assigned E° = 0.00 V
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Measured using a voltmeter in a galvanic cell setup
🔹 3. Electrode Potential Table (E° Series)
Selected E° values (in volts):
| Half-Reaction | E° (V) | Tendency |
|---|---|---|
| F₂ + 2e⁻ → 2F⁻ | +2.87 | Strong oxidizer |
| MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O | +1.51 | Oxidizer |
| Cl₂ + 2e⁻ → 2Cl⁻ | +1.36 | |
| Fe³⁺ + e⁻ → Fe²⁺ | +0.77 | |
| Cu²⁺ + 2e⁻ → Cu | +0.34 | |
| H⁺ + e⁻ → ½H₂ | 0.00 | Reference |
| Zn²⁺ + 2e⁻ → Zn | -0.76 | Reducer |
| Al³⁺ + 3e⁻ → Al | -1.66 | Strong reducer |
| Na⁺ + e⁻ → Na | -2.71 |
🔹 4. Interpretation of E° Values
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A positive E° means the species is a strong oxidizing agent (more likely to gain electrons)
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A negative E° means the species is a strong reducing agent (more likely to lose electrons)
🔹 5. How to Use E° in Redox Prediction
Rule:
In a redox pair, the species with higher E° will be reduced, and the one with lower E° will be oxidized.
🧪 Example 1:
Will Zn(s) displace Cu²⁺ from solution?
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Zn²⁺ + 2e⁻ → Zn (E° = –0.76 V)
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Cu²⁺ + 2e⁻ → Cu (E° = +0.34 V)
Since Zn has a lower E°, it is a stronger reducing agent, so:
✅ Yes, Zn can displace Cu²⁺
🧪 Example 2:
Which is the better oxidizing agent: Fe³⁺ or MnO₄⁻?
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Fe³⁺ + e⁻ → Fe²⁺ (E° = +0.77 V)
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MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ (E° = +1.51 V)
✅ MnO₄⁻ is the stronger oxidizing agent (higher E°)
🔹 6. Applications in NECTA and Real Life
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Predicting redox displacement reactions
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Explaining corrosion (e.g., Fe vs Cu)
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Designing batteries (e.g., Zn–Cu cell)
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Understanding electrolysis and cell potentials
🧠 NECTA Tips
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Always show E° values when comparing two half-cells
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Use E° cell = E°(cathode) – E°(anode)
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Remember: oxidation occurs at lower E°, reduction at higher E°
✅ Summary
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Standard electrode potential (E°) compares redox strength
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Measured against Standard Hydrogen Electrode
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More positive E° = stronger oxidizer
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Use E° differences to predict feasible reactions
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Essential for electrochemistry theory, cell design, and NECTA interpretation