From composition to formula
Quantitative analysis determines how much of each element a compound contains. The empirical formula gives the simplest whole-number atom ratio. The molecular formula gives the actual atom numbers and is a whole-number multiple of the empirical formula.
Percentage-composition workflow
- If percentages are given, assume a convenient 100 g sample so each percentage becomes a mass in grams.
- Convert each mass to moles using n = m/M.
- Divide every mole amount by the smallest.
- Convert near-simple ratios to whole numbers. Ratios near 1.5, 1.33 or 1.25 may require multiplication by 2, 3 or 4 rather than careless rounding.
- Write the empirical formula and check its calculated percentage composition.