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A-LevelChemistryReaction kineticsFeb/Mar 2024Paper 5 Q212 Marks

A student wants to investigate the rate of the hydrolysis of methyl methanoate, HCOOCH3. HCOOCH3 + H2O ⇌ HCOOH + CH3OH The reaction is catalysed by dilute hydrochloric acid, HCl(aq). The amount of methanoic acid, HCOOH, produced as the reaction progresses can be monitored by titration with aqueous sodium hydroxide, NaOH(aq), of known concentration using thymolphthalein as the indicator. To determine this, the volume of NaOH(aq) needed to neutralise the H+(aq) from the catalyst needs to be found beforehand. The student uses the following procedure. step 1 Add approximately 150 cm³ of iced water to a 250 cm³ conical flask, A. step 2 Add 200 cm³ of 0.250 moldm-3 HCl(aq) to a 500 cm³ conical flask, B. Conical flask B is the flask in which the reaction takes place. step 3 Transfer 2.00cm³ of 0.250moldm¯³ HCl(aq) from conical flask B to conical flask A. Carry out a single titration of the contents of conical flask A with NaOH(aq) of known concentration. step 4 Add 10.0cm³ of methyl methanoate to conical flask B, swirl the reaction mixture and immediately start a stopwatch. step 5 After 1 minute transfer 2.00cm³ of the reaction mixture from conical flask B into conical flask A. Carry out a further single titration of the contents of conical flask A against NaOH(aq). Do not empty the contents of conical flask A between titrations. step 6 After 10 minutes transfer 2.00 cm³ of the reaction mixture from conical flask B into conical flask A. Titrate the contents of conical flask A against NaOH(aq). step 7 Repeat step 6 at intervals of 10 minutes for 1 hour.

📋 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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About This A-Level Chemistry Question

Topic

This structured question tests Reaction kinetics in A-Level Chemistry (syllabus code 9701). It is worth 12 marks.

Source

This question appeared in the Cambridge A-Level Chemistry Feb/Mar 2024 examination, Paper 5 Variant 2.

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