Empirical Formula Calculator
Calculate the empirical formula from percent composition data.
Enter up to 5 elements with their mass percentages and get the simplest whole-number ratio.
Empirical Formula
The empirical formula shows the simplest whole-number ratio of atoms in a compound. It may or may not be the same as the molecular formula.
How to determine it from percent composition:
- Assume 100 grams of sample → percentages become grams directly
- Convert grams to moles: n = mass / atomic mass
- Divide all mole values by the smallest one to get ratios
- Round to nearest whole numbers (if close to 0.5, multiply all by 2)
Example: Compound with 40.00% C, 6.71% H, 53.29% O
- C: 40.00/12.011 = 3.330 mol
- H: 6.71/1.008 = 6.657 mol
- O: 53.29/15.999 = 3.331 mol
- Divide by smallest (3.330): C:H:O = 1:2:1
- Empirical formula: CH₂O (formaldehyde, sugars, etc.)
Molecular formula from empirical formula:
Molecular formula = (Empirical formula)_n
n = Molar mass / Empirical formula mass
For CH₂O (emp. mass = 30.03):
- Glucose (M = 180.16): n = 180.16/30.03 = 6 → C₆H₁₂O₆
- Formaldehyde (M = 30.03): n = 1 → CH₂O (empirical = molecular)
- Acetic acid (M = 60.05): n = 2 → C₂H₄O₂
Common empirical formulas vs molecular formulas:
| Empirical | Molecular |
|---|---|
| CH₂O | Glucose C₆H₁₂O₆ |
| CH | Benzene C₆H₆, Ethyne C₂H₂ |
| CH₂ | Ethylene C₂H₄, Cyclohexane C₆H₁₂ |
| HO | Hydrogen peroxide H₂O₂ |
| NaCl | NaCl (empirical = molecular for ionic compounds) |