How do you convert empirical formula to molecular?

1 Answer
Jun 23, 2014

You use the molar mass or molecular mass of a compound to convert its empirical formula to a molecular formula.

For example, assume you know that the empirical formula of a compound is CH₂O.

To determine its molecular formula, you have to do an experiment to find its molecular (molar) mass.

The empirical formula is the simplest formula of a compound. The actual formula is an integral multiple of the empirical formula.

Let's assume that the molecular mass turned out to be about 180 u.

If the empirical formula is CH₂O, the actual formula is #"(CH₂O)"_n# or #C_nH_(2n)O_n#, where #n# = 1, 2, 3, … . Our job is to determine the value of #n#.

The empirical formula mass of CH₂O is 30.03 u. The molecular mass of 180 u must be some multiple of this number.

#n = (180" u")/(30.03" u")# = 6.0 ≈ 6

∴ The molecular formula = #C_nH_(2n)O_n# = C₆H₁₂O₆.

Hope this helps.