A-LevelChemistryChemical energeticsMay/June 2018Paper 3 Q215 Marks
2 In this experiment you will determine the enthalpy change, ∆H, for the decomposition of calcium hydroxide to calcium oxide. Ca(OH)2(s) → CaO(s) + H₂O(I) To do this, you will determine the enthalpy changes for the reactions of calcium hydroxide and calcium oxide with hydrochloric acid. Excess acid will be used for both experiments. You will then use Hess' Law to calculate the enthalpy change for the reaction above. FB 2 is 3.0 mol dm⁻³ hydrochloric acid, HCl. FB 3 is calcium hydroxide, Ca(OH)2. FB 4 is calcium oxide, CaO.
📋 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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