A-LevelChemistryHalogen derivativesMay/June 2025Paper 1 Q331 Mark
Four drops of 1-chlorobutane, 1-bromobutane and 1-iodobutane are put separately into three test-tubes containing 1.0 cm³ of aqueous silver nitrate at 60°C. In each case, a hydrolysis reaction occurs. H2O(l) + R–X(l) + Ag⁺(aq) → R–OH(aq) + AgX(s) + H⁺(aq) R represents C4H9 and X represents the halogen atom. The rate of formation of cloudiness in the test-tubes is in the order RCl < RBr < RI. Why is this?
AThe bond energy of R-X decreases from RCl to RI.
BThe first ionisation energy of the halogen decreases from Cl to I.
CThe solubility of AgX(s) decreases from AgCl to AgI.
DThe R-X bond polarity decreases from RCl to RI.
✓ Correct Answer
The correct answer is A: The bond energy of R-X decreases from RCl to RI.
📋 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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