Year 11 / Chemical reactions — reactants, products and energy change
Count particles by weighing.
A mole contains 6.02214076 × specified entities. Molar mass connects a measurable mass to an amount of substance. Be explicit about whether entities are atoms, molecules or formula units; one mole of water molecules contains two moles of hydrogen atoms.
For an empirical formula, convert each element’s mass to moles and divide by the smallest amount. Multiply all ratios if needed to reach small whole numbers. A molecular formula is a whole-number multiple of the empirical formula, found from molar mass.
Mass and amount
Explore the relationship
n = m/M. Amount counts entities; specify atoms, molecules or formula units.
Amount / mol
Tap or focus a plotted point to read its values.
View plotted data as a table
| Series | Mass / g | Amount / mol |
|---|---|---|
| Amount / mol | 0 | 0 |
| Amount / mol | 1.66667 | 0.0416667 |
| Amount / mol | 3.33333 | 0.0833333 |
| Amount / mol | 5 | 0.125 |
| Amount / mol | 6.66667 | 0.166667 |
| Amount / mol | 8.33333 | 0.208333 |
| Amount / mol | 10 | 0.25 |
| Amount / mol | 11.6667 | 0.291667 |
| Amount / mol | 13.3333 | 0.333333 |
| Amount / mol | 15 | 0.375 |
| Amount / mol | 16.6667 | 0.416667 |
| Amount / mol | 18.3333 | 0.458333 |
| Amount / mol | 20 | 0.5 |
| Amount / mol | 21.6667 | 0.541667 |
| Amount / mol | 23.3333 | 0.583333 |
| Amount / mol | 25 | 0.625 |
| Amount / mol | 26.6667 | 0.666667 |
| Amount / mol | 28.3333 | 0.708333 |
| Amount / mol | 30 | 0.75 |
| Amount / mol | 31.6667 | 0.791667 |
| Amount / mol | 33.3333 | 0.833333 |
| Amount / mol | 35 | 0.875 |
| Amount / mol | 36.6667 | 0.916667 |
| Amount / mol | 38.3333 | 0.958333 |
| Amount / mol | 40 | 1 |
| Amount / mol | 41.6667 | 1.04167 |
| Amount / mol | 43.3333 | 1.08333 |
| Amount / mol | 45 | 1.125 |
| Amount / mol | 46.6667 | 1.16667 |
| Amount / mol | 48.3333 | 1.20833 |
| Amount / mol | 50 | 1.25 |
| Amount / mol | 51.6667 | 1.29167 |
| Amount / mol | 53.3333 | 1.33333 |
| Amount / mol | 55 | 1.375 |
| Amount / mol | 56.6667 | 1.41667 |
| Amount / mol | 58.3333 | 1.45833 |
| Amount / mol | 60 | 1.5 |
| Amount / mol | 61.6667 | 1.54167 |
| Amount / mol | 63.3333 | 1.58333 |
| Amount / mol | 65 | 1.625 |
| Amount / mol | 66.6667 | 1.66667 |
| Amount / mol | 68.3333 | 1.70833 |
| Amount / mol | 70 | 1.75 |
| Amount / mol | 71.6667 | 1.79167 |
| Amount / mol | 73.3333 | 1.83333 |
| Amount / mol | 75 | 1.875 |
| Amount / mol | 76.6667 | 1.91667 |
| Amount / mol | 78.3333 | 1.95833 |
| Amount / mol | 80 | 2 |
| Amount / mol | 81.6667 | 2.04167 |
| Amount / mol | 83.3333 | 2.08333 |
| Amount / mol | 85 | 2.125 |
| Amount / mol | 86.6667 | 2.16667 |
| Amount / mol | 88.3333 | 2.20833 |
| Amount / mol | 90 | 2.25 |
| Amount / mol | 91.6667 | 2.29167 |
| Amount / mol | 93.3333 | 2.33333 |
| Amount / mol | 95 | 2.375 |
| Amount / mol | 96.6667 | 2.41667 |
| Amount / mol | 98.3333 | 2.45833 |
| Amount / mol | 100 | 2.5 |
Explore: Increase molar mass at fixed sample mass. What happens to amount?
A compound contains 12 g carbon and 4 g hydrogen. Use C = 12 and H = 1 g mol⁻¹.
- Amounts are 1 mol C and 4 mol H.
- The simplest ratio is 1:4, giving CH₄.
Assumed knowledge
Relative atomic masses and ratios.
Learning checkpoints & source
YOUR LEARNING CHECKPOINT- Convert mass, moles and particle number.
- Determine empirical and molecular formulas.
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