Empirical Formula Calculator
This calculator determines the empirical formula of a compound from its percent composition by mass. Provide the element symbols and their corresponding percent composition (comma-separated). The tool assumes a 100 g sample for simplicity so that percentages directly convert to grams.
How it works
- Assume a 100 g sample: percentage values become grams.
- Convert grams to moles using atomic weights (grams ÷ atomic mass).
- Divide all mole values by the smallest mole value to get ratios.
- Multiply ratios by the smallest integer to obtain whole-number subscripts.
- Write the empirical formula using element symbols and subscripts.
Empirical Formula Calculation Steps: grams → moles → divide by smallest → multiply to whole numbersExample
Given percent composition: C 40%, H 6.7%, O 53.3%.
Steps:
- Assume 100 g sample: C = 40 g, H = 6.7 g, O = 53.3 g.
- Moles: C: 40 / 12.011 ≈ 3.33 mol; H: 6.7 / 1.008 ≈ 6.65 mol; O: 53.3 / 15.999 ≈ 3.33 mol.
- Divide by smallest (≈3.33): C: 1, H: 2, O: 1 → empirical formula CH2O.
Tips & Common Issues
- Make sure element symbols are correctly capitalized (e.g., Cl, not CL).
- Provide the same number of percentages as elements; the calculator validates the counts.
- If an element is not in the built-in atomic weight table, you will see an error. You can add common elements to the mapping in the calculator component if needed.
Frequently Asked Questions
Q: Why assume a 100 g sample?
A: Percent compositions are relative. Assuming 100 g makes conversion to grams direct and simplifies the mole calculations.
Q: What if the ratios are not exact integers?
A: The calculator attempts small integer multipliers (1–12) to find the simplest whole-number ratio. This mirrors typical lab rounding procedures for empirical formula determination.
Q: Can this give the molecular formula?
A: The empirical formula shows the simplest whole-number ratio of atoms. To get the molecular formula, you also need the compound's molar mass and then determine the multiple between the empirical formula mass and the molecular mass.
When to use
Use this tool for introductory chemistry, stoichiometry problems, lab report analysis, and when interpreting percent composition data to determine empirical formulas.