Lesson Plan

• Describe relative atomic and molecular masses and their role in mass calculations.
• Apply the laws of definite and multiple proportions to set up mass ratios.
• Calculate reactant and product masses in balanced equations using simple proportions without using the mole concept.
• Solve practice problems that require determining unknown masses from given reactant amounts.

• Projector and screen
• Whiteboard and markers
• Printed worksheet with practice questions
• Periodic table handout
• Scientific calculators
• Scale diagram visual (balance illustration)

Begin with a quick demonstration of a balance showing magnesium and oxygen to highlight mass relationships. Review students’ prior knowledge of relative atomic mass and how to write balanced equations. Explain that by the end of the lesson they will be able to determine unknown masses in reactions using simple proportional reasoning.

1. Do‑now (5') – Short quiz on relative atomic masses displayed on the board.
2. Mini‑lecture (10') – Review of relative atomic/molecular masses, laws of proportion, and the proportion method.
3. Guided example (15') – Teacher works through the magnesium combustion calculation while students follow.
4. Pair practice (15') – Students solve practice questions 1 and 2 from the worksheet; teacher circulates to check understanding.
5. Whole‑class discussion (10') – Review answers, clarify misconceptions, and emphasise the use of coefficients.
6. Extension activity (10') – Students tackle the magnesium nitride problem, explaining each step.
7. Exit ticket (5') – Each student writes the mass of chlorine required for 40 g Ca as a quick check.

Recap how relative masses and balanced coefficients give direct mass ratios for reactants and products. Collect exit tickets to gauge mastery of the proportion method. For homework, assign three additional mass‑proportion problems from the textbook to reinforce the skill.