What does percent composition tell you about a molecule?
Percent composition tells you which types of atoms (elements) are present in a molecule and their levels. Percent composition can also tell you about the different elements present in an ionic compound as well.
Let's look at two examples
The molar mass of
The hydrogens make up 2g (since each mole of hydrogen is 1g)
The oxygen makes up 16g.
The percent composition of the compound is:
H = (2g/18g) x 100 = 11.1%
O = (16g/18g) x 100 = 88.9%
Percent composition can be calculated the chemical formula of a compound, or it can be determined experimentally.
Here is a video which discusses how to calculate percent composition from experimental data for a reaction of iron and oxygen which produces an iron oxide compound.
Video from: Noel Pauller
Hope this helps!