This exam focus covers Exam Focus within Purity & Formulations for GCSE Chemistry. Revise Purity & Formulations in Chemical Analysis for GCSE Chemistry with 20 exam-style questions and 12 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 11 of 13 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
Topic position
Section 11 of 13
Practice
20 questions
Recall
12 flashcards
🎯 Exam Focus
Very High Frequency
What Examiners Ask About Purity
- "Explain what is meant by a pure substance" (1 mark) — Say: contains only one type of element or compound
- "Describe how you could test the purity of aspirin" (3 marks) — Measure melting point, compare to literature value (135 °C), pure = sharp melting point at correct temperature
- "Explain why impurities lower the melting point" (2 marks) — Disrupts regular structure, requires less energy to break apart
- "What is a formulation? Give an example" (2 marks) — Designed mixture with each component in a measured quantity; e.g. medicine, paint, petrol
- Data interpretation — You may be given a table of melting point data and asked to identify which sample is most pure (narrowest range, closest to literature value)
AO2 Application Tips
- When given melting point data, always compare range AND temperature to the pure value
- A sample melting over 5+ degrees is definitely impure
- One degree range could still be impure — look for the word "sharp"