Lesson Plan: Redox Reactions

Physical Chemistry

Redox Reactions

This chapter deals with the transfer of electrons. It is the fundamental logic behind batteries, corrosion, and metallurgy. Mastering Oxidation Numbers here is non-negotiable for understanding Class 12 Electrochemistry.

🔋

⚠️ Prerequisites

Chemical Bonding: Understanding Electronegativity is crucial for assigning oxidation states.
Valency: Common charges on ions (e.g., $SO_4^{2-}$, $NO_3^-$).
Stoichiometry: Balancing simple atoms.

🧠 Study Approach

Systematic Process: Balancing redox reactions is algorithmic. Do not try to guess coefficients. Follow the Ion-Electron Method step-by-step strictly (Balance Atom $\to$ O $\to$ H $\to$ Charge).

Study Sequence

1. Classical vs Electronic Concept

Classical: Gain of Oxygen/Loss of Hydrogen (Oxidation).
Modern: Loss of Electrons (Oxidation) / Gain of Electrons (Reduction) - OIL RIG.

2. Oxidation Number (CRITICAL)

Rules for assigning O.N. (Alkali metals +1, O usually -2, H usually +1).
Paradoxes: Fractional O.N. ($S_4O_6^{2-}$), Peroxide linkages ($CrO_5$, $H_2SO_5$). Calculating average vs individual O.N.

3. Types of Redox Reactions

Combination, Decomposition, Displacement (Metal/Non-metal).
Disproportionation: Same element gets oxidized AND reduced (e.g., $H_2O_2 \to H_2O + O_2$).

4. Balancing: Ion-Electron Method

Splitting into Half-Reactions. Balancing atoms other than O/H.
Acidic Medium: Add $H_2O$ for O, $H^+$ for H.
Basic Medium: Balance as acidic, then add $OH^-$ to neutralize $H^+$.

5. Redox Titrations

Concept of n-factor (Change in O.N. per molecule).
Examples: Permanganometry ($KMnO_4$ self-indicator), Iodometry ($I_2/Na_2S_2O_3$ using Starch).

6. Electrochemical Cells

Redox Couple. Daniel Cell ($Zn-Cu$): Anode (-ve, Oxidation) vs Cathode (+ve, Reduction). Salt Bridge function. Standard Electrode Potential ($E^\circ$).

🎯 How to Practice

Structure Drawing: Don't rely on algebra for "Paradox" cases. Draw the Butterfly structure of $CrO_5$ to see the Peroxide linkage (-1) vs Oxide (-2).

The Balancing Drill: Pick 5 reactions (e.g., $MnO_4^-$ with $Fe^{2+}$, $C_2O_4^{2-}$, $I^-$). Balance them in Acidic medium until you can do it without looking at the steps.

Disproportionation Check: Always identify the element undergoing both oxidation and reduction (e.g., $P_4 + NaOH \to PH_3 + NaH_2PO_2$).

📝 Quick Revision Notes

Oxidation Number Rules

Group 1 Metals: Always $+1$
Fluorine: Always $-1$
Oxygen: $-2$ (Oxide), $-1$ (Peroxide), $-1/2$ (Superoxide), $+2$ (in $OF_2$)

Balancing Sequence

Atom $\to$ Oxygen ($H_2O$) $\to$ Hydrogen ($H^+$) $\to$ Charge ($e^-$)

Mnemonics

OIL RIG

LEO GER

Oxidation Is Loss, Reduction Is Gain

Search This Blog