Lesson Plan

• Describe the difference between empirical and molecular formulae.
• Calculate an empirical formula from percent‑composition data.
• Determine the molecular formula using the compound’s molar mass and its empirical formula.
• Identify common errors when converting empirical to molecular formulae.
• Apply the step‑by‑step procedure to solve practice problems independently.

• Projector or interactive whiteboard
• Printed worksheet with example problem
• Flowchart handout showing steps from empirical to molecular formula
• Periodic‑table posters
• Calculators (or spreadsheet access)
• Molecular model kits (optional)

Begin with a quick question: “What makes glucose different from its empirical formula CH₂O?” This links everyday chemistry to the concept of molecular formulae. Review students’ prior knowledge of atomic masses and percent composition. Explain that by the end of the lesson they will be able to write the correct molecular formula for any compound given its empirical formula and molar mass.

1. Do‑now (5 min): Mini‑quiz – convert a simple % composition to an empirical formula.
2. Mini‑lecture (10 min): Definitions of empirical vs. molecular formula; introduce the equation n = M₍compound₎ / M₍emp₎.
3. Guided example (15 min): Work through the glucose example on the board while students follow in their worksheets.
4. Pair activity (15 min): Students calculate the molecular formula for the first practice question; teacher circulates to check understanding.
5. Whole‑class discussion (10 min): Share answers, highlight common pitfalls (rounding n, precision of atomic masses).
6. Exit ticket (5 min): Write one step of the procedure they found most challenging.

Summarise the five‑step process: determine empirical formula, find its relative mass, divide the compound’s molar mass to get n, and multiply subscripts. Collect exit tickets to gauge which step needs reinforcement. For homework, students complete the remaining two practice questions and bring any uncertainties to the next class.