TCE Chemistry — Level 4
Redox Titration — Flashcards & Quiz
Redox titration determines the concentration of an oxidising or reducing agent by titrating against a standard of known concentration. TCE Chemistry Level 4 commonly uses permanganate (MnO₄⁻) or dichromate (Cr₂O₇²⁻) as the oxidising titrant, and asks you to balance the half-equations, combine them for the net ionic equation, and calculate the unknown concentration from the titre.
Key Points
- Permanganate (MnO₄⁻) in acidic solution reduces to Mn²⁺: MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O.
- Dichromate (Cr₂O₇²⁻) in acidic solution reduces to Cr³⁺: Cr₂O₇²⁻ + 14H⁺ + 6e⁻ → 2Cr³⁺ + 7H₂O.
- Permanganate is self-indicating — the endpoint is marked by a persistent pink colour when excess MnO₄⁻ is added.
- Dichromate needs an indicator (e.g. diphenylamine sulfonate) because the colour change is less obvious.
- Balancing: balance atoms first, then charges with electrons, then combine half-equations to cancel electrons.
- Calculation: use stoichiometric ratios from the balanced equation to relate moles of titrant to moles of analyte.
Common Mistakes to Avoid
- Forgetting the acidic conditions required for permanganate and dichromate.
- Not balancing half-equations before combining them.
- Using the wrong stoichiometric ratio when calculating concentrations.
- Missing that permanganate is self-indicating and doesn't need an external indicator.
- Reading the burette at the wrong point — meniscus, eye level.
Exam Strategy
TASC Level 4 redox titration questions ask you to balance equations and calculate unknowns. Method: (1) identify the oxidising and reducing agents, (2) balance each half-equation, (3) combine to cancel electrons, (4) use stoichiometry to relate moles, (5) calculate concentration. Show each step explicitly for full marks.
Sample Flashcards
Q1: How is a redox titration calculation different from an acid-base one?
The method is the same (n = cV, mole ratio, c = n ÷ V), but the mole ratio comes from the balanced redox equation built from half-equations. Potassium permanganate is self-indicating: the purple MnO₄⁻ is reduced to almost colourless Mn²⁺, so the first permanent pink colour marks the end point.
Sample Quiz Questions
Q1: In the titration of Fe²⁺ with acidified MnO₄⁻, the two react in a 1 : 1 mole ratio.
Answer: FALSE
MnO₄⁻ + 5Fe²⁺ + 8H⁺ → Mn²⁺ + 5Fe³⁺ + 4H₂O: one MnO₄⁻ gains five electrons, so the ratio is 1 : 5.
Revision Tip
Redox titration calculations are procedural — drill a Revizi deck with permanganate and dichromate titrations against iron, oxalate, and hydrogen peroxide.
Related Concepts
Last updated: 9 October 2026 · 1 sample flashcards · 1 sample quiz questions