A-LevelChemistryAnalytical techniquesOct/Nov 2025Paper 3 Q115 Marks
Hydrated ethanedioic acid is a diprotic acid with the formula (COOH)2•xH2O where x is an integer. Ethanedioic acid reacts with manganate(VII) ions when heated. 5(COOH)2(aq) + 2MnO4¯(aq) + 6H+(aq) → 10CO2(g) + 2Mn2+(aq) + 8H2O(l) You will determine the value of x in (COOH)2•xH2O by titrating a solution containing ethanedioic acid with manganate(VII) ions. • FA 1 is 6.20 g dm⁻³ aqueous ethanedioic acid, (COOH)2•xH2O. • FA 2 is 0.0200 mol dm⁻³ potassium manganate(VII), KMnO4. • FA 3 is 1.0 mol dm⁻³ sulfuric acid, H2SO4·
📋 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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