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A-LevelChemistryAnalytical techniquesOct/Nov 2018Paper 4 Q67 Marks

The isoelectric point is the pH at which an amino acid exists as a zwitterion. The isoelectric point of valine is 6.0 and of lysine is 9.8. A mixture of the dipeptide, val-lys, and its two constituent amino acids, valine and lysine, was analysed by electrophoresis using a buffer at pH 6.0.

Q: What topic does this question test?

This question tests Analytical techniques in A-Level Chemistry (syllabus code 9701). It is worth 7 marks.

📋 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 Analytical techniques in A-Level Chemistry (syllabus code 9701). It is worth 7 marks.

Source

This question appeared in the Cambridge A-Level Chemistry Oct/Nov 2018 examination, Paper 4 Variant 1.

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