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Science

Moles and Stoichiometry

Overview

Students explore how chemists measure amounts of substances and calculate the exact quantities needed for reactions, connecting the microscopic world of atoms to measurable masses.

Learning Objective
Students understand the mole concept and can use stoichiometry to calculate the quantities of reactants and products in chemical reactions.

Resources needed

  • None — or a periodic table for molar masses

Lesson stages

0 / 7 done
  1. 1 Ask: how do chemists count atoms when they are too small to see individually?
  2. 2 Introduce the mole: one mole of any substance contains 6.02 x 10^23 particles (Avogadro's number).
  3. 3 Explain molar mass: the mass in grams of one mole of a substance — numerically equal to its relative atomic or formula mass.
  4. 4 Example: one mole of carbon = 12 g; one mole of water (H2O) = 18 g.
  5. 5 Calculate moles from mass: moles = mass divided by molar mass.
  6. 6 Apply to a reaction: magnesium + oxygen gives magnesium oxide. Balance the equation: 2Mg + O2 gives 2MgO.
  7. 7 Calculate: if 24 g of magnesium reacts (2 moles), how many grams of magnesium oxide are produced? (80 g — 2 moles of MgO at 40 g/mol).

Tap a step to mark it as done.

Variations

  • Calculate the percentage composition of a compound by mass.
  • Introduce empirical formulas — determine the simplest whole number ratio from experimental data.
  • Apply moles to gas volumes: at standard conditions, one mole of any gas occupies 24 litres.
More information

Teach: mole, Avogadro, molar mass, stoichiometry, balance, equation, ratio. The mole is simply a counting unit — like a dozen is 12, a mole is 6.02 x 10^23. This analogy makes the concept accessible.

Focus on converting between grams and moles before introducing stoichiometric ratios from balanced equations.

Can students calculate the number of moles in a given mass of a substance? Can they use a balanced equation to calculate the mass of product formed from a known mass of reactant?

No resources needed. Draw balanced equations in soil. All calculations require only the periodic table for molar masses — this can be hand-drawn for the elements being studied.

Students often think the mole is a very complex concept. It is simply a number — just as a pair means 2 and a dozen means 12, a mole means 6.02 x 10^23. The difficulty is in applying it, not in understanding what it is.

Stoichiometry is the most practically important skill in quantitative chemistry. It underpins industrial chemistry, pharmaceutical production, and food science — any process that requires specific amounts of chemicals to be combined.

Activity details
Secondary Challenging 30 minutes no prep Small Group, Whole Class Indoor & Outdoor
Topics
Moles Stoichiometry Quantitative Chemistry