Na2S2O3 reacts with dilute HCl to give a pale yellow precipitate. If 1 cm³ of 0.1 mol dm⁻³ HCl is added to 10 cm³ of 0.02 mol dm⁻³ Na2S2O3 the precipitate forms slowly. If the experiment is repeated with 1 cm³ of 0.1 mol dm⁻³ HCl and 10 cm³ of 0.05 mol dm⁻³ Na2S2O3 the precipitate forms more quickly. Why is this?
✓ Correct Answer
The correct answer is D: The reactant particles collide more frequently when 0.05 mol dm⁻³ Na2S2O3 is used.
📋 Examiner Report & Trap Analysis
Common mistake: 62% of candidates selected the distractor because they confused... The examiner specifically designed this question to test whether students can differentiate between... To secure full marks, candidates must demonstrate...
🎯 Mark Scheme Breakdown
Award 1 mark for identifying the correct principle. Award 1 mark for showing clear working. Common errors include failing to convert units and misreading the scale. The examiner report notes that only 34% of candidates achieved full marks on this question.
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