A-LevelChemistryAnalytical techniquesOct/Nov 2017Paper 3 Q114 Marks
In this experiment you will determine the oxidation number of iodine in one of its compounds by titration. FA 1 is a 0.0197 mol dm-³ solution of the iodine-containing compound. FA 2 is dilute sulfuric acid, H₂SO₄. FA 3 is aqueous potassium iodide, KI. FA 4 is 0.105 mol dm-³ sodium thiosulfate, Na₂S₂O₃. starch indicator FA 1 reacts with excess acidified potassium iodide to produce iodine, I₂. This iodine is then titrated with aqueous sodium thiosulfate using starch indicator.
📋 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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