A-LevelChemistryAtoms, molecules and stoichiometryOct/Nov 2020Paper 1 Q51 Mark
A white powder is known to be a mixture of magnesium oxide and aluminium oxide. 100 cm³ of 2 mol dm⁻³ NaOH(aq) is just enough to dissolve the aluminium oxide in x grams of the mixture. The reaction is shown. Al₂O₃ + 2OH¯ + 3H₂O → 2Al(OH)₄¯ 800 cm³ of 2 mol dm⁻³ HCl(aq) is just enough to dissolve all of the oxide in x grams of the mixture. The reactions are shown. Al₂O₃ + 6H⁺ → 2Al³⁺ + 3H₂O MgO + 2H⁺ → Mg²⁺ + H₂O How many moles of each oxide are present in x grams of the mixture?
A0.05 | 0.25
B0.05 | 0.50
C0.10 | 0.25
D0.10 | 0.50
✓ Correct Answer
The correct answer is D: 0.10 | 0.50
📋 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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