BASED ON FORMULAE
7.8 - Determination of Empirical Formula
In section 7.7, we learned
that percent composition establishes the relative proportions of the elements
in a compound in terms of mass. From a given
chemical formula, we learned to generate a list of percent compositions of the
elements that make up the compound.
In this section, we will carry out the opposite task. We will
be given the percent compositions of the elements that make up the compound.
From that, we will derive the chemical formula of the compound.
An analysis of a substance shows that it is made up of
and oxygen. The percentage composition of the
elements in the compound are determined to be:
39.10 % carbon,
8.77 % hydrogen, and
52.13 % oxygen.
From the above data we can derive the
ratio of carbon, hydrogen and oxygen in the substance. We will put it in the
y and z are the
simplest whole-number ratio of carbon, hydrogen
to oxygen of the substance. This chemical formula is called the empirical
formula of a substance.
empirical formula of the above example is C3H8O3*.
* It should be noted
that the empirical formula may or may not be the
true chemical formula of the substance. We will examine this in greater detail
in section 7.9.
Section 8.5 Calculation
of Empirical (Simplest) and Molecular Formulas..p200