| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Chemistry |
| Lesson Topic: Identify redox reactions by the colour changes involved when using acidified aqueous potassium manganate(VII) or aqueous potassium iodide |
Learning Objective/s:
- Describe the characteristic colour changes of acidified KMnO₄ and KI indicators during redox tests.
- Explain how these colour changes reveal whether a substance is an oxidising or a reducing agent.
- Apply the KMnO₄ and KI tests to identify the redox behaviour of unknown samples.
- Interpret test results using a decision‑tree and avoid common pitfalls such as pH effects and contaminations.
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Materials Needed:
- Projector and whiteboard
- Test tubes, pipettes, and safety goggles
- Acidified KMnO₄ solution (purple)
- KI solution (colourless)
- Starch solution
- Sample solutions: oxalic acid, H₂O₂, FeSO₄, sulphite, thiosulphate
- Worksheet / practice question handout
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Introduction:
Begin with a quick “redox detective” hook: students will predict electron‑transfer outcomes by watching colour changes. Review that KMnO₄ is deep‑purple and KI is colourless, linking these to oxidation states. State the success criteria – students will correctly predict and record the colour changes for a set of reactions.
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Lesson Structure:
- Do‑now (5'): Write expected colour change for a given reagent (KMnO₄ or KI) on a sticky note.
- Mini‑lecture (10'): Explain the chemistry behind the indicator colours and the redox half‑reactions.
- Teacher demonstration (15'): Show KMnO₄ test on oxalic acid, H₂O₂ and FeSO₄, noting decolourisation and any gas evolution.
- Guided lab (15'): In pairs, students add KI to sulphite and thiosulphate samples, then add starch to confirm iodine (blue‑black).
- Decision‑tree activity (10'): Groups classify unknown samples as oxidiser, reducer, both, or neither using the colour‑change results.
- Check for understanding (5'): Quick quiz via clickers on which colour change indicates which type of agent.
- Wrap‑up (5'): Review objectives and clarify any misconceptions.
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Conclusion:
Summarise that loss of purple KMnO₄ signals a reducing agent, while appearance of brown‑violet (or blue‑black with starch) iodine signals an oxidising agent. Exit ticket: each student writes one example of a substance that decolourises KMnO₄ and one that produces iodine with KI. Homework: complete the worksheet with three additional redox scenarios.
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