A student uses paper chromatography to investigate two food colourings, X and Y. Food colouring X produces three spots and food colouring Y produces one spot. Explain what the chromatography results tell the student about the composition of each food colouring.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Food colouring X gives three spots, so it contains three different components – it is a mixture, not a pure compound.
Food colouring Y gives one spot, so it contains only one component – it is a pure substance (a single compound).
Food colouring Y gives one spot, so it contains only one component – it is a pure substance (a single compound).
Examiner tips
- Use the word ‘mixture’ for more than one spot and ‘pure substance’ for one spot. Mention the number of spots directly. Keep the answer short – 4 marks only.
- Avoid saying ‘contains more than one compound’ – just state ‘mixture’ and ‘pure substance’.
Mark scheme (4 marks)
- Food colouring X is a mixture (not a pure compound)
- Because it produces more than one spot / three spots indicate three different components/compounds are present
- Food colouring Y is a pure substance / a single compound
- Because a pure compound produces a single spot (in all solvents) / one spot shows only one component is present
Key terms in this question
Related
- All AQA GCSE Chemistry (8462) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →