Video Transcript
The numbers of carbon, hydrogen,
and oxygen atoms in a molecule are in the ratio two to six to two. What is the empirical formula of
this molecule?
An empirical formula is a chemical
formula that indicates the elements in a molecule and the simplest whole number
ratio of atoms of each element. This is not to be confused with a
molecular formula, which is the chemical formula that expresses the exact number of
atoms of each element in a molecule. For example, a molecule of glucose
has the molecular formula C6H12O6. This means that one molecule of
glucose contains exactly six atoms of carbon, 12 atoms of hydrogen, and six atoms of
oxygen. This also means that the ratio of
carbon to hydrogen to oxygen atoms in the molecule is six to 12 to six.
If we simplified the ratio by
dividing by six, the greatest common factor, we would get the simplest whole number
ratio, one to two to one. Matching up the ratio with the
chemical symbols, we can write the empirical formula, CH2O. So if we know the molecular formula
or the ratio of atoms in a molecule, we can determine the empirical formula by
dividing by the greatest common factor.
In the question, we are told that
the ratio of carbon to hydrogen to oxygen atoms in a molecule is two to six to
two. The greatest common factor of two
and six is two, so we need to divide each of the values by two to determine the
simplest whole number ratio. So the simplest whole number ratio
of carbon to hydrogen to oxygen atoms is one to three to one. We can write these values as
subscripts after the appropriate element to construct the empirical formula. A value of one is omitted from a
chemical formula. Removing these subscripts gives us
the empirical formula CH3O.
So a molecule that has a ratio of
carbon to hydrogen to oxygen atoms of two to six to two has an empirical formula of
CH3O.
