| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Chemistry |
| Lesson Topic: Describe how paper chromatography is used to separate mixtures of soluble coloured substances, using a suitable solvent |
Learning Objective/s:
- Describe the principle of paper chromatography and the roles of the stationary and mobile phases.
- Calculate and interpret Rf values for coloured substances.
- Perform a paper chromatography experiment to separate a mixture of food colourings.
- Analyse factors that affect separation and suggest improvements.
- Apply chromatography results to identify unknown coloured substances.
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Materials Needed:
- Chromatography paper (2 cm × 15 cm strips)
- Pencil and ruler
- Capillary tubes or fine glass rods
- Solvent mixture (e.g., water/ethanol)
- Developing chamber (beaker with lid)
- Safety goggles and gloves
- Ruler for measuring distances
- Worksheet for recording observations and Rf calculations
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Introduction:
Begin with a quick demonstration of a coloured spot moving up paper when a solvent is added, asking students what they observe. Recall prior knowledge of solubility and capillary action. Explain that today they will learn how paper chromatography separates mixtures and will be able to calculate Rf values to interpret results.
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Lesson Structure:
- Do‑now (5'): Students label a diagram of a chromatography setup and predict solvent movement (check understanding).
- Mini‑lecture (10'): Explain the principle, stationary/mobile phases, and how to calculate Rf values.
- Demonstration (10'): Teacher shows spotting, preparing the developing chamber, and solvent front development.
- Guided practical (20'): Pairs conduct the experiment, measure distances, and calculate Rf values.
- Data analysis discussion (10'): Groups compare Rf values and discuss factors influencing separation.
- Exit‑ticket quiz (5'): One short question on interpreting an Rf value.
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Conclusion:
Summarise that paper chromatography separates components based on differential solubility, producing measurable Rf values. Ask students to write one key factor that influences separation as an exit ticket. For homework, they will research another chromatography technique and prepare a short summary.
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