A-LevelChemistryAnalytical techniquesMay/June 2025Paper 3 Q218 Marks
You will determine the percentage purity of another sample of calcium carbonate, CaCO3, by titration. The experiment involves three steps. step 1 A known mass of the same impure calcium carbonate, FA 1, is reacted with an excess of hydrochloric acid to form FA 3. This step has been done for you. step 2 You will dilute the products of step 1 to a known volume. step 3 You will carry out a titration to find out how much acid remains after the reaction in step 1. FA 3 has been prepared by reacting 19.0g of FA 1 with 250cm³ of 2.00moldm⁻³ hydrochloric acid, HCl. FA 5 is 0.0900 moldm⁻³ sodium hydroxide, NaOH. FA 6 is bromophenol blue indicator.
📋 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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