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
#H_2O#is 18 g/mol
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!
Here is an example for the compound C2HO4
You will first need to find the molar mass of the compound.
C = 2 x 12 = 24
O = 1 x 16 = 16
H = 4 x 1 = 4
Total mass = 40 amu
To find the percent composition you divide each part by the whole and multiply by 100 to convert to a %.
C = (24/44) x 100 = 54.5%
O = (16/44) x 100 = 36.4%
H = (4/44) x 100 = 9.1%
Percent composition can also be calculated using experimental data. The video below shows you how to do that type of calculation.
Percent composition in chemistry typically refers to the percent each element is of the compound's total mass.
The basic equation = mass of element / mass of compound X 100%
For instance, if you had a 80.0 g sample of a compound that was 20.0 g element X and 60.0 g element y then the percent composition of each element would be:
Element X = 20.0 g X / 80.0 g total x 100% = .250 or 25.0 %
Element Y = 60.0 g Y / 80.0 g total x 100 % = .750 or 75.0 %
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