example above, we set the formula up as follows:
TIP
This type of question always appears on the test.Another Example
Find the percent compositions of Cu and H 2 O in the compound CuSO 4 · 5H 2 O
(the dot is read “with”).
First, we calculate the formula mass:
and then find the percentages:
Percentage Cu:Percentage H 2 O:When you are given the percentage of each element in a compound, you can
find the empirical formula as shown with the following example:
Given that a compound is composed of 60.0% Mg and 40.0% O, find the
empirical formula of the compound.