A-LevelChemistryReaction kineticsOct/Nov 2021Paper 5 Q219 Marks
Halogenoalkanes undergo hydrolysis with aqueous sodium hydroxide to form alcohols. e.g. CH3CH2CH2CH2Br(l) + NaOH(aq) → CH3CH2CH2CH2OH(l) + NaBr(aq) A student carried out an experiment to compare the rate at which three halogenoalkanes, 1-chlorobutane, CH3CH2CH2CH2Cl, 1-bromobutane, CH3CH2CH2CH2Br, and 1-iodobutane, CH3CH2CH2CH2I, undergo hydrolysis. The method used was as follows: • Place a 5 cm³ sample of each halogenoalkane into separate test-tubes. • Add 1 cm³ of organic solvent to each test-tube. • Add 2 cm³ aqueous sodium hydroxide to each test-tube. • Add 3 drops of acid-base indicator to the mixture. • Heat the test-tubes in a thermostatically controlled, electrically heated water bath. • Record the time taken for the indicator to change colour.
📋 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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