Lesson Plan

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Lesson Plan
Grade: A‑Level Date: 17/01/2026
Subject: Chemistry
Lesson Topic: Chromatography: principles, paper, thin layer, column, gas-liquid
Learning Objective/s:

  • Describe the principle of chromatography and define key terms such as stationary phase, mobile phase, Rf and retention time.
  • Compare paper, thin‑layer, column and gas‑liquid chromatography in terms of principle, applications and limitations.
  • Perform basic paper and TLC experiments, calculate Rf values and interpret the results.
  • Explain how a gas‑liquid chromatograph separates volatile compounds and how retention time and peak area relate to composition.
  • Evaluate which chromatographic method is most suitable for a given sample in an exam scenario.
Materials Needed:

  • Projector or interactive whiteboard
  • PowerPoint/slide deck on chromatography theory
  • Sample solutions (e.g., food dyes, pigments)
  • Chromatography paper, TLC plates, developing chambers
  • Solvents (ethanol, hexane, solvent mixtures)
  • Capillary tubes or micropipettes
  • UV lamp or iodine chamber for visualisation
  • Worksheets/handouts with Rf calculation tables
 Introduction:

Begin with a quick demonstration of a colourful paper‑chromatogram to spark curiosity about how mixtures can be separated. Ask students what separation methods they have already used and link this to the concept of a stationary and mobile phase. State that by the end of the lesson they will be able to choose and carry out the appropriate chromatographic technique and interpret its results.
Lesson Structure:

  1. Do‑now (5’) – Short quiz on previous separation techniques; students submit answers on mini‑whiteboards.
  2. Mini‑lecture (10’) – Explain chromatography principles, terminology and the role of Rf and retention time.
  3. Paper chromatography demonstration (10’) – Teacher runs a demo, students record solvent front and calculate Rf values.
  4. Guided TLC activity (15’) – In groups, students spot samples, develop plates, visualise under UV, calculate Rf and compare with standards.
  5. Overview of column and gas‑liquid chromatography (10’) – Discuss set‑up, key parameters, show short video of a GC run.
  6. Check for understanding (5’) – Exit ticket: match each technique to a real‑world application and list one advantage.
Conclusion:

Recap the main differences between the four chromatographic methods and emphasise how to select the most efficient technique for a given sample. Collect exit tickets to gauge understanding and clarify any lingering misconceptions. For homework, students complete a worksheet that requires them to design a chromatography experiment for a provided mixture and predict expected Rf or retention times.