Simulic
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The Mole, Molar Mass and Avogadro's Number – Counting Particles by Weighing

ChemistryAtomic Structure & Periodic TableAges 15–16

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Put two samples on a balance (elements, water, table salt, limestone, table sugar), compare equal masses or equal amounts in moles, and drag the slider. The simulation works out the molar mass from the formula, the amount n = m/M and the number of particles N = n × Nₐ. Magnifiers show the ratio of particle numbers, the balance tips when the masses differ, and a log scale with comparisons (grains of sand, counting, a stack of paper) shows how huge Avogadro's number is.

Lesson: The mole, molar mass and the Avogadro constant

What it shows

A mole is the amount of substance that contains exactly 6.02214076 × 10²³ particles, the Avogadro constant. Because the molar mass in g/mol has the same value as the mass of one particle in atomic mass units, a balance can count atoms: 12.01 g of carbon and 18.02 g of water each hold about 6.02 × 10²³ particles. The simulation adds up the relative atomic masses in a formula to get M, then uses n = m/M and N = n × Nₐ. Equal masses of different substances contain different numbers of particles; equal amounts in moles contain equal numbers but have different masses.

How to use

Choose Substance A and Substance B, then pick Same mass or Same amount (mol) under Compare. Drag the slider, or drag sideways on the balance, and watch the pans, the magnifiers and the table. Read how the molar mass is built from the formula. Under Picture the number of A, switch between the comparisons to feel the size of Avogadro's number.

Parameters you can change

  • Substance A Carbon (graphite) – C, Aluminium – Al, Iron – Fe, Copper – Cu, Silver – Ag, Gold – Au, Water – H₂O, Table salt – NaCl, Limestone – CaCO₃, Table sugar – C₁₂H₂₂O₁₁
  • Substance B Carbon (graphite) – C, Aluminium – Al, Iron – Fe, Copper – Cu, Silver – Ag, Gold – Au, Water – H₂O, Table salt – NaCl, Limestone – CaCO₃, Table sugar – C₁₂H₂₂O₁₁
  • Compare the two samples Same mass, Same amount (mol)
  • Mass of each sample (when comparing equal masses) 1–200 g
  • Amount of each sample (when comparing equal amounts) 0.05–5 mol
  • Picture the number of particles Sand covering the land, Counting one by one, Stack of paper

Questions to explore

  1. Do 12 g of carbon and 12 g of copper contain the same number of atoms? Which has more, and how many times more?
  2. Why does the balance tip with 1 mol of water and 1 mol of sucrose, although both contain the same number of molecules?
  3. What is the molar mass of CaCO₃ from the relative atomic masses, and does the simulation agree?

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