Determine the simplest whole-number ratio of atoms from percent composition or mass data
Enter element symbols (C, H, O, N, etc.) and their masses or percentages
The empirical formula calculator determines the simplest whole-number ratio of atoms in a compound from percent composition or mass data. It converts masses to moles, finds the smallest mole ratio, and reduces to the simplest integer subscripts to give the empirical formula.
Step 1: Convert to Moles
moles = mass / atomic mass
Step 2: Find Smallest Moles
Identify the element with the fewest moles
Step 3: Calculate Ratios
ratio = moles of element / smallest moles
Step 4: Convert to Whole Numbers
Round ratios or multiply by 2, 3, etc. to get integers
Given Composition
40.0% C, 6.7% H, 53.3% O
Assume 100g sample: 40.0g C, 6.7g H, 53.3g O
Convert to Moles
C: 40.0g / 12.01 g/mol = 3.33 mol
H: 6.7g / 1.008 g/mol = 6.65 mol
O: 53.3g / 16.00 g/mol = 3.33 mol
Divide by Smallest (3.33)
C: 3.33 / 3.33 = 1
H: 6.65 / 3.33 = 2
O: 3.33 / 3.33 = 1
Result
Empirical Formula: CH₂O
Using incorrect atomic masses
Always use accurate atomic masses from periodic table
Rounding too early
Keep extra decimals until final step to avoid errors
Not recognizing fractions
1.5 → multiply by 2, 1.33 → multiply by 3
Confusing empirical and molecular
Empirical is simplest ratio, molecular is actual formula
Find actual molecular formula from empirical
Calculate % by mass of each element
Calculate molecular weight
An empirical formula shows the simplest whole-number ratio of atoms in a compound. For example, glucose (C₆H₁₂O₆) has the empirical formula CH₂O because the ratio 6:12:6 simplifies to 1:2:1.
The empirical formula is the simplest ratio, while the molecular formula is the actual number of atoms. For example, ethene (C₂H₄) and benzene (C₆H₆) both have the empirical formula CH, but different molecular formulas.
Yes! Percent composition works the same way. Just assume a 100g sample, so 40% becomes 40g, 6.7% becomes 6.7g, etc. Then proceed with the normal calculation.
Multiply all ratios to get whole numbers: 1.5 → multiply by 2 (gives 3:2), 1.33 → multiply by 3 (gives 4:3), 1.25 → multiply by 4 (gives 5:4). The calculator does this automatically.
Divide the molecular mass by the empirical formula mass to get a multiplier (n). Then multiply all subscripts in the empirical formula by n. Example: if CH₂O has molecular mass 180 g/mol, n = 180/30 = 6, so molecular formula is C₆H₁₂O₆.
Assuming 100g makes the math simple because percentages directly convert to grams. 40% becomes 40g, which is easier to work with. The ratios remain the same regardless of sample size.
Yes! Many compounds share empirical formulas. CH is shared by ethene (C₂H₄), benzene (C₆H₆), and acetylene (C₂H₂). CH₂O is shared by formaldehyde (CH₂O), glucose (C₆H₁₂O₆), and acetic acid (C₂H₄O₂).
If you know some percentages, subtract from 100% to find the missing element. For example, if you have 40% C and 6.7% H, then O = 100% - 40% - 6.7% = 53.3%. This assumes the compound only contains those elements.
Education
General chemistry and stoichiometry courses
Laboratory
Determining unknown compound formulas
Industry
Quality control and material analysis
Research
Characterizing new compounds and synthesis products