Half-life and experimental techniques Quiz
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5 questions, one answer each
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1. Three half-lives measured from different starting concentrations on a concentration–time graph are all 40 s. What is the order?
- A. Zero
- B. First
- C. Second
- D. Third
2. Which method is suitable for following CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)?
- A. Measure the mass lost as CO₂ escapes
- B. Colorimetry
- C. Titrate samples with sodium thiosulfate
- D. Use a conductivity probe in a gas jar
3. In an iodine clock reaction, why is 1/t proportional to the initial rate?
- A. Thiosulfate catalyses the reaction
- B. Starch speeds up the reaction
- C. The same amount of iodine is formed before the colour appears in every experiment
- D. The reaction stops when the colour appears
4. Why is a sample added to excess sodium hydrogencarbonate before being titrated?
- A. To dissolve the iodine
- B. To react with the thiosulfate
- C. To make the starch end-point sharper
- D. To neutralise the acid catalyst and stop the reaction
5. A 10.0 cm³ sample needs 20.0 cm³ of 0.0100 mol dm⁻³ sodium thiosulfate. What is the concentration of iodine in the sample?
- A. 0.0050 mol dm⁻³
- B. 0.0100 mol dm⁻³
- C. 0.0200 mol dm⁻³
- D. 0.0400 mol dm⁻³