Empirical Formula Calculator

What is an Empirical Formula?

The empirical formula is the simplest whole-number ratio of atoms in a compound. For example, glucose has a molecular formula of C₆H₁₂O₆, but its empirical formula is CH₂O (a 1:2:1 ratio).

Steps to Determine the Empirical Formula

1. Start with percentages or masses of each element in the compound
2. Convert to moles by dividing each mass by the element's atomic mass
3. Find the mole ratio by dividing all mole values by the smallest
4. Round to whole numbers. If ratios are not close to whole numbers, multiply all ratios by a common factor (e.g., multiply by 2 if a ratio is ~0.5, by 3 if ~0.33)

Empirical vs. Molecular Formula

The molecular formula shows the actual number of atoms in one molecule. It is always a whole-number multiple of the empirical formula:

Molecular Formula = (Empirical Formula) × n

n = Molar Mass / Empirical Formula Mass

To find the molecular formula, you need the compound's molar mass (from mass spectrometry or other methods).

Examples

• Water: 88.9% O, 11.1% H → Empirical formula: H₂O (also the molecular formula)
• Glucose: 40.0% C, 6.7% H, 53.3% O → Empirical: CH₂O, Molecular: C₆H₁₂O₆
• Acetic acid: 40.0% C, 6.7% H, 53.3% O → Empirical: CH₂O, Molecular: C₂H₄O₂