| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Chemistry |
| Lesson Topic: Describe the test to distinguish between saturated and unsaturated hydrocarbons by their reaction with aqueous bromine |
Learning Objective/s:
- Describe the bromine test principle and how it differentiates saturated and unsaturated hydrocarbons.
- Predict the colour‑change outcome for alkanes, alkenes, and alkynes when exposed to aqueous bromine.
- Perform the bromine test safely and record observations accurately.
- Explain the chemical reaction that causes decolourisation of unsaturated hydrocarbons.
- Evaluate common errors in the test and suggest corrective actions.
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Materials Needed:
- Aqueous bromine solution (≈0.1 % Br₂)
- Clean, dry test tubes and labels
- Hydrocarbon samples (alkane, alkene, alkyne) or solutions in CCl₄
- Distilled water (control)
- Safety gear: goggles, gloves, lab coat
- Pipettes or droppers
- Waste collection container for bromine
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Introduction:
Begin with a quick demonstration of a coloured bromine solution and ask students what might happen if it contacts different hydrocarbons. Recall prior knowledge of double and triple bonds and their reactivity. Explain that today’s success criteria are to correctly carry out the bromine test, interpret the colour change, and link it to the presence of unsaturation.
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Lesson Structure:
- Do‑now (5') – Short question on C=C reactivity to activate prior knowledge.
- Mini‑lecture (10') – Explain the bromine test principle, safety precautions, and expected observations.
- Teacher demonstration (5') – Add bromine to a known alkane and show the colour remains.
- Guided lab activity (20') – Pairs perform the test on provided samples, record colour changes.
- Group discussion (5') – Compare results, identify which samples are unsaturated.
- Error analysis (5') – Review common pitfalls and how to avoid them.
- Exit ticket quiz (5') – Students write the expected observation for an alkene and its interpretation.
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Conclusion:
Summarise that decolourisation indicates the presence of C=C or C≡C bonds, while no change confirms saturation. Collect an exit ticket where each student describes one observation and its interpretation. For homework, assign students to write the balanced addition reaction for a given alkene and reflect on the safety considerations of handling bromine.
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