Empirical Formula Calculator

The empirical formula is the simplest whole-number ratio (CH2O). The molecular formula shows the actual number of atoms (C6H12O6). The molecular formula is always a whole-number multiple of the empirical formula. Some compounds, like H2O and CO2, have identical empirical and molecular formulas because their ratios are already in simplest form.

Yes. Formaldehyde (CH2O, MW 30), acetic acid (C2H4O2, MW 60), and glucose (C6H12O6, MW 180) all share the empirical formula CH2O. They are distinguished by their molecular weights, which give multipliers of 1, 2, and 6 respectively.

If analysis gives percentages for some elements but not all, assume the remaining percentage is the unlisted element. For example, if combustion analysis of an organic compound gives 52.2% C and 13.0% H, then oxygen is 100 - 52.2 - 13.0 = 34.8% (assuming only C, H, O are present).

Combustion analysis burns an organic sample in excess oxygen. All carbon converts to CO2 (measured by mass) and all hydrogen converts to H2O (measured by mass). From the CO2 mass, calculate grams of C; from H2O mass, calculate grams of H. Any remaining mass is typically oxygen. This method is reliable, fast, and requires only milligram quantities of sample.

For accurate empirical formula determination, mass percentages should be known to at least two decimal places. Errors greater than 0.5% can change the apparent ratio and lead to incorrect formulas. Modern CHN analyzers achieve precision of 0.1-0.3%, which is usually sufficient for unambiguous empirical formula determination.