How to use this calculator
- Enter the empirical formula.
- Enter the measured molar mass in g/mol.
- Calculate and verify that the mass ratio is close to a positive integer.
Formula and variables
multiple = measured molar mass / empirical formula mass
| Symbol | Meaning | Unit |
|---|---|---|
| M | measured molar mass | g/mol |
| Mₑ | empirical formula mass | g/mol |
| k | formula multiple | integer |
Worked example
An empirical formula CH2O and measured molar mass near 180.16 g/mol gives a multiplier of 6 and molecular formula C6H12O6.
Interpretation
The molecular formula is accepted only when the mass ratio is an integer within the stated tolerance.
Common mistakes
- Use the empirical formula, not a percentage list.
- Do not force a non-integral measured mass ratio.
Frequently asked questions
How is a molecular formula different from an empirical formula?
An empirical formula gives the smallest ratio. A molecular formula gives the actual atom counts.
Why can the calculator reject a measured molar mass?
The molecular mass must be an integer multiple of the empirical formula mass within the stated tolerance.
Does this tool identify a formula from exact mass alone?
No. This tool requires an empirical formula. Exact-mass formula searches need element and charge constraints.
Can I use scientific notation?
Yes. Enter values such as 6.022e23 or 1.0e-6 in a numeric field.
How should I round the result?
Keep extra digits during the calculation. Round the final result to the precision required by your data.