How are empirical and molecular formulas related?

Question

Henry Antrim · Accepted Answer

The molecular formula is always a whole number multiple of the empirical formula.

The molecular formula is always a whole number ratio of the empirical formula, which is by definition the simplest whole number ratio defining constituent atoms in a species.

#"Molecular formula"# #=# #"(Empirical formula)"xxn#.

Of course, #n# MIGHT equal #1#.

Typically an organic compound would be combusted where its combustion products, #CO_2# and #H_2O# could be measured very accurately against a standard; #N# content (as #N_2# or #NO_2#) could also be measured very accurately on a gas chromatograph.

With the help of these data, an empirical formula can be computed, and the molecular formula can be adduced given a molecular mass (obtained through other means).

Thus, the lesson to be learned is:

#"Molecular formula"# #=# #"(Empirical formula)"xxn#.

And of course #n#, the multiplier, may be #1#.

Is that right?

Henry Antrim · Answer

undefined The empirical formula represents the simplest whole number ratio of atoms in a compound, while the molecular formula gives the actual number of each type of atom in a molecule.