Redox Reactions and Electrode Processes

NCERT Reference:Chapter 7 – Redox Reactions– Page 127–129 (Part I)

Quick Notes

Redox reactions are central to electrochemical processes.
Oxidation occurs at the anode and reduction occurs at the cathode.
Electrochemical cell: Converts chemical energy into electrical energy.
Electrolytic cell: Converts electrical energy into chemical energy.
Standard electrode potential (E°) is a measure of the tendency of a species to gain electrons.

More positive E° → greater tendency to be reduced.

Electrode potential values help predict the direction of redox reactions.

Full Notes

This section explores how redox reactions can drive electrical energy when electrons flow through an external circuit – forming the basis of electrochemical cells.

Recap – Direct Redox Reaction

When a zinc rod is placed in a solution of copper sulfate:

NCERT 11 Chemistry diagram showing a zinc rod dipped in copper sulfate where zinc is oxidised to Zn²⁺ and Cu²⁺ is reduced to copper metal.

Zinc is oxidised to Zn²⁺ by losing electrons.
Copper ions are reduced to copper metal by gaining those electrons.
Electrons transfer directly from Zn to Cu²⁺.
Energy (as heat) is released during the reaction as it is exothermic (−ΔH).

Indirect Electron Transfer (Electrochemical Cell)

To harness energy released in redox reactions as electrical energy, we must separate the oxidation and reduction half-reactions.

For Example Using zinc and copper.

Experimental Setup:

NCERT 11 Chemistry Daniell cell diagram with Zn/Zn²⁺ anode, Cu/Cu²⁺ cathode, salt bridge and external wire allowing electron flow.

Beaker 1: Zn rod in ZnSO₄ solution
Beaker 2: Cu rod in CuSO₄ solution
Connected by:
- A salt bridge (e.g., KCl or NH₄NO₃ in agar) to allow ion migration and complete the circuit
- A metallic wire to conduct electrons between electrodes

This setup is known as a Daniell Cell.

Now, electrons flow through an external circuit to get to the copper half cell for the reduction of Cu²⁺ ions. This flowing of electrons is electrical energy and can be used as an energy transfer.

Redox Couples

A redox couple consists of the oxidised and reduced forms of a substance.

In the above example:
- Zn²⁺/Zn is the redox couple at the oxidation site
- Cu²⁺/Cu is the redox couple at the reduction site

Observations

Electron Flow: Electrons move through the wire from Zn to Cu, generating current.
Ion Flow: Ions migrate through the salt bridge to balance charge between solutions.

Electrode Potential

For more detail on electrode potentials see NCERT 12 Chapter 2.

Each electrode develops a potential, depending on its tendency to gain or lose electrons.
When measured against a standard, this is called Standard Electrode Potential (E°).
The Standard Hydrogen Electrode (SHE) is assigned E° = 0.00 V and used as a reference.

Interpreting E° Values

A negative E° means the species is a strong reducing agent (readily loses electrons).
A positive E° means it's a weaker reducing agent compared to H₂/H⁺.

In Class 12, you’ll explore these electrode potentials in detail, including how to calculate EMF and apply this to electrochemical and galvanic cells.

Summary

Redox processes drive electron flow that can be channelled as electrical energy.
Oxidation occurs at the anode and reduction at the cathode.
Separating half-reactions in a Daniell cell allows useful electrical work.
Standard electrode potentials compare reduction tendencies and help predict reaction direction.