Redox titrations Quiz
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5 questions, one answer each
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1. Why must hydrochloric acid not be used when titrating with MnO₄⁻?
- A. HCl reduces Fe³⁺ to Fe²⁺ so the titre is too small
- B. HCl is too weak an acid
- C. MnO₄⁻ oxidises Cl⁻ to Cl₂ so the titre is too large
- D. Cl⁻ ions form a precipitate with Mn²⁺
2. What is the end-point in the titration of Fe²⁺ with MnO₄⁻?
- A. The first permanent pale pink
- B. Colourless to blue-black
- C. Purple to brown
- D. Yellow to colourless
3. 20.0 cm³ of 0.0100 mol dm⁻³ MnO₄⁻ reacts exactly with Fe²⁺. What amount of Fe²⁺ was present?
- A. 2.00 × 10⁻⁴ mol
- B. 4.00 × 10⁻⁵ mol
- C. 1.00 × 10⁻² mol
- D. 1.00 × 10⁻³ mol
4. When is starch added in the thiosulfate–iodine titration?
- A. At the start
- B. Near the end-point, when the solution is pale yellow
- C. After the end-point
- D. Only after the colour has become blue-black
5. A burette is read to ±0.05 cm³. What is the percentage uncertainty in a titre of 20.00 cm³?
- A. 0.25%
- B. 0.10%
- C. 0.50%
- D. 1.0%