Empirical Formula
- Percentage composition by mass gives a ratio by mass of the elements contained in a compound
- This ratio by mass can be converted to a ratio by moles if the % figures (or the known mass) are divided by the respective relative atomic masses
- Ratios of moles will seldom be whole number ratios
- To calculate the ratio of numbers or atoms in the empirical formula divide all the mole ratios by the smallest calculated mole value
- The amount of water associated with a particular salt (water of crystallisation) can be calculated using this method as
| Step | Calcium | Bromine |
| 1 – % By Mass (or Mass) | 20% | 80% |
| 2 – Mole Ratio | 20/40 = 0.5 | 80/80 = 1 |
| 3 – Ratio by atoms | 0.5/0.5 = 1 | 1/0.5 = 2 |
| 4- Empirical Formula | Ca = 1 | Br = 2 |
Percentage Yield – the percentage of the reactants that are converted to products. In some reactions this will be 100% but others it is much less than 100%.
Theoretical Yield – the amount of a substance that should be produced through a chemical reaction Actual Yield – the amount of a substance that is actually produced through a chemical reaction
