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DrX Whiz Niraj
Redox Titrations: Oxidation & Reduction
Master the foundational concepts of Redox Titrations. Learn about Classical, Electronic, and Oxidation Number concepts in detail for your B.Pharm exams.
The term REDOX is made up of two words: REDuction and OXidation. A redox titration is a volumetric analysis based on an electron transfer reaction between the titrant and the analyte.
In any redox reaction, oxidation and reduction always occur simultaneously. One substance loses electrons (gets oxidized), while another substance gains those exact same electrons (gets reduced).
The Golden Mnemonic: "OIL RIG"
Oxidation Is Loss (of electrons)
Reduction Is Gain (of electrons)
Historically and scientifically, oxidation and reduction can be defined using three different concepts:
1. Classical Concept
Based on Oxygen and Hydrogen transfer.
- Oxidation: Addition of Oxygen OR removal of Hydrogen.
(e.g., C + O₂ → CO₂) - Reduction: Addition of Hydrogen OR removal of Oxygen.
(e.g., CuO + H₂ → Cu + H₂O)
2. Electronic Concept
Based entirely on the transfer of electrons (Modern concept).
- Oxidation: Complete or partial Loss of one or more electrons by an atom or ion.
- Reduction: Complete or partial Gain of one or more electrons by an atom or ion.
3. Oxidation Number
Based on the apparent charge an atom possesses.
- Oxidation: An Increase in the oxidation number.
(e.g., Fe²⁺ → Fe³⁺ + e⁻) - Reduction: A Decrease in the oxidation number.
(e.g., Cl₂ + 2e⁻ → 2Cl⁻)
| Agent Type | Definition | What happens to it? | Common Examples in Titration |
|---|---|---|---|
| Oxidizing Agent (Oxidant) |
A substance that accepts electrons from another substance. | It undergoes Reduction. (Its oxidation number decreases) |
KMnO₄ (Potassium Permanganate), K₂Cr₂O₇, I₂ (Iodine). |
| Reducing Agent (Reductant) |
A substance that donates electrons to another substance. | It undergoes Oxidation. (Its oxidation number increases) |
Na₂S₂O₃ (Sodium Thiosulphate), Oxalic Acid, FeSO₄. |
Practical Alert: Auto-Indicators
In many redox titrations, you don't need to add an external indicator! The titrant itself acts as a Self-Indicator.
The classic example is Potassium Permanganate (KMnO₄). It is intensely purple in the burette. As it reacts and gets reduced (to Mn²⁺), it becomes colorless. At the exact end point, when all the analyte is consumed, a single drop of unreacted KMnO₄ turns the entire flask Faint Pink.