Redox titration is a type of titration in which the reaction between the titrant and the analyte involves a transfer of electrons, i.e., oxidation and reduction. It is used to determine the concentration of an oxidizing or reducing agent.
Basic Idea
- Redox reactions involve electron transfer:
- Oxidation: Loss of electrons
- Reduction: Gain of electrons
- In redox titration, the amount of electrons exchanged is used to find the concentration of one of the reactants.
How It Works
- Setup:
- A solution of unknown concentration is placed in a flask.
- A titrant of known concentration (either oxidizing or reducing agent) is added from a burette.
- An indicator that changes color at a specific redox potential may be used, or the reaction itself may be self-indicating.
- Reaction Progress:
- As titrant is added, the oxidation or reduction of the analyte occurs.
- At the equivalence point, the stoichiometric amount of titrant has reacted with the analyte.
- Endpoint Detection:
- Some redox reactions are self-indicating (e.g., permanganate titrations, where MnO₄⁻ is purple and disappears upon reduction).
- Others require a redox indicator (like ferroin, diphenylamine).
Examples
- Permanganometry:
- Titration of Fe²⁺ with KMnO₄
- Reaction: 5Fe²⁺ + MnO₄⁻ + 8H⁺ → 5Fe³⁺ + Mn²⁺ + 4H₂O
- Endpoint: The appearance of a faint pink color indicates all Fe²⁺ is oxidized.
- Iodometry/Iodimetry:
- Titration of Cu²⁺ with Na₂S₂O₃ via iodine liberation
- Reaction involves oxidation and reduction steps.
- Endpoint detected with starch indicator (blue color disappears).
- Cerimetry:
- Using Ce⁴⁺ as a titrant to oxidize Fe²⁺.
- The endpoint is detected by a redox indicator.
Significance
- Redox titrations are widely used when acid-base titration is not possible.
- Important in pharmaceuticals, water analysis, and metal content determination.
- Can be used for both oxidizing and reducing agents.