A-LevelChemistryReaction kineticsMay/June 2022Paper 5 Q218 Marks
In a neutral solution, aqueous potassium iodide acts as a catalyst for the decomposition of aqueous hydrogen peroxide. 2H2O2(aq) → 2H2O(l) + O2(g) A student plans to carry out an investigation to find how temperature affects the initial rate of the decomposition of aqueous hydrogen peroxide, H2O2(aq), in the presence of aqueous potassium iodide, KI(aq). The student knows that the initial rate of the reaction can be measured by timing the production of the oxygen. The student carries out a series of experiments. In experiment 1 the student notes the temperature of the H2O2(aq) and KI(aq) under room conditions. The solutions are mixed in apparatus designed to collect the oxygen produced. A stop-watch is started at the beginning of the reaction. The volume of oxygen is noted at regular time intervals. In experiments 2–8 the solutions are heated to different temperatures before mixing and measurement of the oxygen produced. The data collected is used to determine a value for the activation energy of the decomposition of H2O2(aq) in the presence of KI(aq).
📋 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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