A-LevelChemistryReaction kineticsOct/Nov 2020Paper 3 Q27 Marks
When a solution containing thiosulfate ions, S2O32-, is acidified the following reaction occurs. S2O32-(aq) + 2H+(aq) → S(s) + SO2(g) + H₂O(l) The solid sulfur that is formed makes the mixture become cloudy. The rate of reaction can then be measured by timing how long it takes for the mixture to become too cloudy to see through. You will investigate how changing the concentration of the thiosulfate ions affects the rate of reaction. Throughout these experiments care must be taken to avoid inhaling the SO₂ that is produced. It is very important that as soon as each experiment is complete the contents of the beaker are emptied into the quenching bath. FA 4 is 2.00 mol dm⁻³ hydrochloric acid, HCl. FA 5 is a solution of sodium thiosulfate, Na2S2O3. distilled water
📋 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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