A-LevelChemistryAnalytical techniquesOct/Nov 2025Paper 4 Q67 Marks
(a) Thin-layer and gas/liquid chromatography can be used to separate mixtures into their individual components. (i) Define the following terms used in chromatography. Rf value retention time [2] (ii) Each type of chromatography makes use of a stationary phase and a mobile phase. Complete Table 6.1 with a description of each of these. [Table 6.1] [1] (b) A mixture of two substances A and B is analysed by thin-layer chromatography. The Rf value of substance A is larger than that of substance B. Suggest why substance A has a larger Rf value. [1] (c) The two isomeric compounds Y and Z are analysed by proton (1H) NMR spectroscopy. [Figure Y.Y] (i) Complete Table 6.2 to predict the number of peaks observed in the proton (1H) NMR spectra for Y and Z. [Table 6.2] [1] (ii) Name all the different splitting patterns observed in the proton (1H) NMR spectra for Y and Z. Y Z [2]
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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...
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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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