A-LevelChemistryChemical energeticsMay/June 2021Paper 3 Q211 Marks
When anhydrous sodium carbonate dissolves in water the following reaction occurs. Na2CO3(s) + aq → 2Na+(aq) + CO32-(aq) The enthalpy change for this reaction is the enthalpy change of solution of anhydrous sodium carbonate. Its value is -28.1 kJ mol-1. You will use this information to find the percentage purity of an impure sample of anhydrous sodium carbonate. FB 3 is a sample of impure anhydrous sodium carbonate.
📋 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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