Identifying Oxidizing & Reducing Agents
Based on Standard Electrode Potential ($E^\circ$) | Electrochemistry
1. Standard Electrode Potential ($E^\circ$)
The standard electrode potential generally refers to the Standard Reduction Potential. It is a measure of the tendency of a species to gain electrons (get reduced).
Convention: By IUPAC standards, Standard Electrode Potential = Standard Reduction Potential.
2. The Golden Rules
To identify the nature of an agent, look at its $E^\circ$ value:
$$ \text{Higher } E^\circ \text{ (+ve)} \Rightarrow \text{Stronger Oxidizing Agent} $$
$$ \text{Lower } E^\circ \text{ (-ve)} \Rightarrow \text{Stronger Reducing Agent} $$
- High Positive $E^\circ$: The species loves to gain electrons (get reduced). Therefore, it is a strong Oxidizing Agent.
- High Negative $E^\circ$: The species loves to lose electrons (get oxidized). Therefore, it is a strong Reducing Agent.
3. The Electrochemical Series Trends
| Element/Ion | Reaction (Reduction) | $E^\circ$ (Volts) | Nature |
|---|---|---|---|
| Fluorine ($F_2$) | $F_2 + 2e^- \rightarrow 2F^-$ | +2.87 | Best Oxidizing Agent |
| ... | ... | ... | (Increasing Reducing Power) |
| Hydrogen ($H^+$) | $2H^+ + 2e^- \rightarrow H_2$ | 0.00 | Reference |
| ... | ... | ... | (Decreasing Oxidizing Power) |
| Lithium ($Li^+$) | $Li^+ + e^- \rightarrow Li$ | -3.05 | Best Reducing Agent |
4. Predicting Feasibility of Reaction
For a redox reaction to be spontaneous, the overall cell potential ($E^\circ_{cell}$) must be positive.
$$ E^\circ_{cell} = E^\circ_{cathode} - E^\circ_{anode} > 0 $$In simple terms: A substance with higher $E^\circ$ will oxidize (take electrons from) a substance with lower $E^\circ$.
Rule: A metal with lower $E^\circ$ (more negative) will displace a metal with higher $E^\circ$ from its salt solution.
Example: $Zn$ ($E^\circ=-0.76$) displaces $Cu$ ($E^\circ=+0.34$).
Example: $Zn$ ($E^\circ=-0.76$) displaces $Cu$ ($E^\circ=+0.34$).
Practice Quiz
Given standard potentials are in Volts. Identify the agents.
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