Oxidizing & Reducing Agents from Electrode Potential | Electrochemistry

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 $Cu$ ($E^\circ=+0.34$).

Practice Quiz

Given standard potentials are in Volts. Identify the agents.