Describe how paper chromatography can be used to find out whether a sample of ink contains a mixture of dyes or a single pure dye. Include in your answer how you would interpret the result.

Cambridge International IGCSE Chemistry (0620) — 12.3 Chromatography · Describe · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

1. Place a small spot of the ink on a pencil‑lined baseline of chromatography paper.
2. Immerse the paper in a suitable solvent, ensuring the solvent level is below the ink spot.
3. Allow the solvent to rise; it carries the dyes upward and the dyes separate, travelling different distances.
4. If the chromatogram shows a single spot, the ink contains one pure dye; if more than one spot appears, the ink is a mixture of dyes.

Examiner tips

  • Use the exact sequence of steps; examiners look for the solvent level below the spot. Show that separation is due to different distances travelled. Explain the interpretation of one spot vs. multiple spots. Use correct terminology: chromatogram, solvent front, spot.

Common mistakes

  • Not specifying that the solvent level must be below the baseline. Failing to mention that separation is due to different distances travelled. Confusing the solvent front with the ink spot or misinterpreting a single spot as a mixture.

Mark scheme (4 marks)

  1. A spot of the ink is placed on the baseline of the chromatography paper (using a pencil line)
  2. The paper is placed in a suitable solvent so the solvent level is below the baseline / spot
  3. The solvent travels up the paper, carrying the dyes with it / dyes separate as they travel different distances
  4. A single spot on the chromatogram shows a pure single dye; more than one spot shows the ink is a mixture

Key terms in this question

chromatography · mixture

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