How would you calculate the empirical formula of acetic acid (CH3COOH)?

You would divide the numbers of each atom in the molecular formula by their highest common factor.

The empirical formula is the simplest possible formula for a compound.

The subscripts of the in the empirical formula must be in the smallest possible ratio.

We can write the molecular formula ##"CH"_3"COOH"## as ##"C"_2"H"_4"O"_2##.

The ratios of ##"C:H:O"## are ##2:4:2##.

The highest common factor of ##2## and ##4## is ##2##.

We can divide each of these numbers by ##2## to get the ratio

##"C:H:O" = 1:2:1##

The empirical formula of acetic acid is then ##"CH"_2"O"##.