Redox Titration

Titration Animation

Analyte Solution Titrant (from burette) Drops Added

Potential E vs Volume Titrant

Volume Added: 0.00 mL

Current E: 0.00 V

Equivalence Point: 0.00 mL

Equivalence Point Jump Region

Jump Range: 0.00 V

Midpoint E: 0.00 V

Redox Indicators

Current Color:

Indicator E°: 0.00 V

In Range: No

Redox Titration Controls

Analyte (Being Titrated)

Analyte Type: E°(Ox/Red): 0.77 V

Standard reduction potential of analyte

[Analyte]₀: 0.100 M Initial Volume: 25.0 mL Electrons (n): 1

Titrant (Added from Burette)

Titrant Type: E°(Ox/Red): 1.51 V

Standard reduction potential of titrant

[Titrant]₀: 0.020 M Electrons (n): 5

Redox Indicator

Indicator: Indicator E°: 0.76 V

Color change when E≈E°±0.06V

Reduced Color: Oxidized Color:

Titration Control

Volume to Add: 0.00 mL Temperature: 25 °C

Affects Nernst equation (RT/nF)

Common Titrations

Redox Titration Equations

Redox Half-Reaction: Ox + ne⁻ ⇌ Red

Nernst Equation: E = E° - (RT/nF)ln([Red]/[Ox])

At 25°C (298K): E = E° - (0.0592/n)log₁₀([Red]/[Ox])

Equivalence Point: E = (n₁E₁° + n₂E₂°)/(n₁ + n₂)

Before EP (Analyte): E = E°(analyte) - (0.0592/n)log([Red]/[Ox])

After EP (Titrant): E = E°(titrant) - (0.0592/n)log([Red]/[Ox])

Indicator Requirement: E°(indicator) ≈ E at equivalence point

What is Redox Titration?

Redox titration is a volumetric analysis technique based on oxidation-reduction reactions. It involves the transfer of electrons between the analyte and titrant. The potential of the solution changes as titrant is added, creating a characteristic S-shaped curve with a sharp jump at the equivalence point. The equivalence point potential is calculated from the standard potentials of both redox couples. Redox indicators change color at specific potentials, marking the endpoint.

The Nernst Equation in Titration

Fundamental Equation: E = E° - (RT/nF)ln(Q).
At 25°C: E = E° - (0.0592/n)log₁₀([Red]/[Ox]).
Before EP: Use analyte's redox couple.
After EP: Use titrant's redox couple.
At EP: E = (n₁E₁° + n₂E₂°)/(n₁ + n₂).

Equivalence Point Characteristics

Definition: Where electrons lost = electrons gained.
Calculation: V(ep) = (n(analyte) × C(analyte) × V₀)/(n(titrant) × C(titrant)).
Potential: E(ep) = (n₁E₁° + n₂E₂°)/(n₁ + n₂).
Jump Size: Larger ΔE° = sharper endpoint.

Redox Indicators

Principle: Redox-active molecules that change color when oxidized/reduced.
Range: E° ± 0.06V at 25°C.
Selection: E°(indicator) ≈ E at EP.
Common: Diphenylamine (0.76V), Ferroin (1.06V).

Common Redox Titrations

Permanganometry: Self-indicating; used for Fe²⁺, C₂O₄²⁻.
Cerimetry: Strong oxidant; stable solutions.
Dichrometry: Stable primary standard.
Iodometry: Starch indicator (blue).

Titration Curve Analysis

Shape: Sigmoidal (S-shaped).
Equivalence Point: Steepest point on curve.
Jump Size: Larger ΔE° = larger jump.

Factors Affecting Redox Titrations

Temperature: Affects RT/nF term.
pH: Many couples are pH-dependent.
Ionic Strength: Affects activity coefficients.
Catalysts: Some reactions require catalysis.

Real-World Applications

Environmental: COD using dichromate.
Food: Peroxide value, vitamin C.
Pharmaceuticals: Assay of reducing agents.
Water Treatment: Chlorine residual.
Clinical: Glucose, uric acid measurements.