Redox titrations Quiz
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5 questions, one answer each
Each answer is checked as you go, with why.
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1. Why is dilute sulfuric acid, rather than hydrochloric acid, used in an iron(II) titration with manganate(VII)?
- A. Hydrochloric acid is too weak
- B. Sulfuric acid reacts with Fe²⁺
- C. Hydrochloric acid would reduce Fe³⁺
- D. Cl⁻ ions would be oxidised by MnO₄⁻, giving a titre that is too large
2. 20.0 cm³ of 0.0150 mol dm⁻³ MnO₄⁻ react exactly with an acidified Fe²⁺ solution. How many moles of Fe²⁺ were present?
- A. 6.00 × 10⁻⁵ mol
- B. 3.00 × 10⁻⁴ mol
- C. 1.50 × 10⁻³ mol
- D. 1.50 × 10⁻² mol
3. When should starch be added in an iodine–thiosulfate titration?
- A. At the very start
- B. When the iodine solution has faded to pale yellow
- C. After the end-point
- D. Never; thiosulfate is its own indicator
4. What is the mole ratio of I₂ to S₂O₃²⁻ in the titration reaction?
- A. 1 : 2
- B. 1 : 1
- C. 2 : 1
- D. 1 : 4
5. Why is no indicator needed in a titration using potassium manganate(VII)?
- A. MnO₄⁻ is colourless
- B. MnO₄⁻ is purple and its excess gives a permanent pink colour at the end-point
- C. Fe²⁺ changes colour
- D. The acid acts as the indicator