Lesson Plan

• Describe how melting point and boiling point identify substances and indicate purity.
• Explain the correct procedures for determining melting and boiling points.
• Analyse experimental MP/BP data to assess purity and compare with literature values.
• Apply error‑minimisation techniques to improve measurement reliability.
• Calculate impurity concentration from a melting‑point depression.

• Melting‑point apparatus with capillary tubes and thermometer.
• Boiling‑point apparatus (round‑bottom flask, condenser, heating mantle, temperature probe).
• Analytical balance (±0.001 g).
• Desiccator and drying oven.
• Calibrated thermometers or digital temperature probes.
• Sample substances (e.g., NaCl, sucrose, benzoic acid).
• Safety goggles, lab coat, gloves.

Begin with a quick demonstration of an unknown solid melting at a lower temperature than expected to spark curiosity. Review students’ prior knowledge of physical properties and why sharp melting/boiling points signify purity. Explain that today they will learn to measure MP and BP, interpret the results, and use them to confirm identity and purity. Success will be shown by accurate data that matches literature within ±1 °C.

1. Do‑now (5'): Students list physical properties that can identify a substance.
2. Mini‑lecture (10'): Theory of MP/BP as purity indicators; show literature table.
3. Demonstration (10'): Teacher demonstrates melting‑point determination, emphasizing sample preparation and heating rate.
4. Guided practice (15'): Pairs determine the MP of a provided solid, recording onset and clear temperatures.
5. Boiling‑point activity (15'): Students set up the boiling‑point apparatus for a liquid sample and record the stable temperature.
6. Data analysis (10'): Groups compare results with literature, discuss deviations, and calculate impurity percentage for one sample.
7. Error‑check discussion (5'): Review common sources of error and mitigation strategies.
8. Exit ticket (5'): Each student writes one key takeaway and one lingering question.

Summarise that sharp, accurate MP/BP values confirm identity while deviations signal impurities. Students complete an exit ticket stating the most reliable indicator of purity they observed. For homework, they research the melting point of a household substance and predict its purity based on a hypothetical measurement.