A-LevelChemistryGroup 2Oct/Nov 2021Paper 2 Q213 Marks
The reaction scheme shows some reactions of calcium. [Figure: Reaction scheme showing Ca(s) to Ca(NO₃)₂(aq) via HNO₃ (reaction 1), then to Ca(OH)₂(aq) via NaOH(aq). From Ca(OH)₂(aq) to CaO(s) via heat (reaction 2, CO₂(g) byproduct), then from CaO(s) to CaCO₃(s) + H₂O(l) (reaction 3, excess CO₂(g) involved). From CaCO₃(s) + H₂O(l) to Ca(HCO₃)₂(aq) via excess CO₂(g). Also from CaO(s) to CaC₂(s) via C(s) (reaction 4).]
📋 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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