How do you determine the molecular formula from the empirical formula?

To determine a molecular formula from an empirical formula, you need both the empirical formula and the molar mass of the compound.

Steps in words (no equations):

1. Find the empirical formula of the compound (simplest ratio of atoms).
   • Example: CH₂O.
2. Calculate the mass of the empirical formula by adding up the atomic masses of the elements in it.
   • For CH₂O, the mass is about 30 grams per mole.
3. Compare the compound’s actual molar mass (given from experiment) with the mass of the empirical formula.
   • Divide the compound’s molar mass by the empirical formula mass.
   • This gives a whole number multiplier.
4. Multiply all the subscripts in the empirical formula by this whole number to get the molecular formula.
   • If the molar mass is 180 grams per mole, then 180 ÷ 30 = 6.
   • Multiply CH₂O by 6 → C₆H₁₂O₆ (glucose).

In short:
Molecular formula = Empirical formula × Multiplier,
where the multiplier is found by comparing the actual molar mass with the empirical formula mass.