A-LevelChemistryEquilibriaOct/Nov 2017Paper 1 Q341 Mark
Methanoic acid, HCO2H, and hydrocyanic acid, HCN, can both behave as acids. A solution of methanoic acid has a lower pH than a solution of hydrocyanic acid of the same concentration. Which statements explain this? 1 HCO2H molecules dissociate more fully than HCN molecules do. 2 Each HCO2H molecule has two hydrogen atoms; each HCN molecule only has one. 3 Methanoic acid is a weaker acid than hydrocyanic acid.
A1, 2 and 3 are correct
B1 and 2 only are correct
C2 and 3 only are correct
D1 only is correct
✓ Correct Answer
The correct answer is D: 1 only is correct
📋 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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