Lesson Plan

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Lesson Plan
Grade: Date: 17/01/2026
Subject: Chemistry
Lesson Topic: Infra-red spectroscopy: principles, interpretation
Learning Objective/s:
  • Describe the principle of IR absorption and the relationship between vibrational transitions and dipole‑moment change.
  • Identify the main components of an FT‑IR spectrometer and explain their functions.
  • Interpret key absorption bands in the functional‑group and fingerprint regions of an IR spectrum.
  • Prepare solid, liquid and gas samples for IR analysis using appropriate techniques.
  • Correlate observed IR peaks with molecular structure and predict the functional groups present.
Materials Needed:
  • FT‑IR spectrometer (or classroom IR demo unit)
  • KBr powder and pellet press
  • IR‑transparent cells (NaCl, CaF₂ windows)
  • Sample set (solid, liquid, gas examples)
  • Projector or interactive whiteboard
  • Handouts of typical absorption ranges and example spectra
  • Worksheet for spectrum interpretation
 Introduction:
Begin with a short video clip showing how infrared light interacts with molecules, prompting students to consider why some bonds absorb IR while others do not. Recall prior learning about molecular vibrations and dipole moments, then outline today’s success criteria: students will be able to explain IR principles, recognise instrument components, and interpret an unknown spectrum.
Lesson Structure:
  1. Do‑now (5') – Label vibrational modes on a diagram and predict which are IR‑active.
  2. Mini‑lecture (10') – Explain IR absorption principle, energy equation, and functional‑group vs fingerprint regions.
  3. Instrument demo (10') – Show FT‑IR interferometer schematic and discuss source, interferometer, detector, and sample compartment.
  4. Sample preparation lab (15') – Students prepare a KBr pellet and a liquid film, recording observations.
  5. Guided spectrum analysis (15') – Work through an example spectrum, identify peaks, and match to functional groups using the handout.
  6. Collaborative check (5') – Quick quiz (exit ticket) on peak assignments.
  7. Reflection & homework (5') – Summarise key points; assign practice spectra for homework.
Conclusion:
Summarise how IR spectroscopy provides structural information through characteristic absorptions and the importance of proper sample preparation. Students complete an exit ticket matching peaks to functional groups, and for homework they will analyse a provided spectrum and write a brief report.