A-LevelChemistryAnalytical techniquesMay/June 2017Paper 3 Q112 Marks
In this experiment you will determine the relative formula mass of a copper salt by titration. A solution of the copper salt reacts with excess acidified potassium iodide, producing iodine. This iodine is then titrated with aqueous sodium thiosulfate, using starch indicator. FA 1 is an aqueous solution of the copper salt prepared by dissolving 26.0g of the salt to make 1.00 dm³ of solution. FA 2 is dilute sulfuric acid, H2SO4. FA 3 is aqueous potassium iodide, KI. FA 4 is 0.110 moldm⁻³ sodium thiosulfate, Na2S2O3. 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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