The formula of ethanol is therefore C 0.50 H 1.5 O 0.25 (we round off the number of
moles to two signifi cant fi gures). Because the number of atoms must be an integer,
we divide the subscripts by 0.25, the smallest subscript, and obtain for the empirical
formula C 2 H 6 O.
Now we can better understand the word “empirical,” which literally means “based
only on observation and measurement.” The empirical formula of ethanol is determined
from analysis of the compound in terms of its component elements. No knowledge
of how the atoms are linked together in the compound is required.