How to calculate percent composition by mass.

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Hi! My name is Sarah and today I will teach you
how to calculate percent composition by mass.

The first step in calculating the percent composition by mass
is to find the atomic mass of each element in a molecule.
You can find this in the Periodic Table right below the element
symbol. For example, in the case of H2O known as water, you
would have to look up the atomic number for Hydrogen and
and Oxygen on the periodic table. Once you have looked up
the atomic masses for the elements, you see that Hydrogen has
a atomic mass of 1.008 and Oxygen has the atomic mass of 16.

The second step in the process is to find the mass combination
of each element.This means to determine the mass of each element
in the molecule. For H2O you take the mass of Hydrogen and
multiply it by two in order to get the mass of the element for the
molecule. The mass of Oxygen will be left alone as there is only one
atom of Oxygen and not two unlike Hydrogen. So what you are
doing is multiplying the number of atoms of an element with the
atomic mass of that element. For H2O, Hydrogen will have a mass
of 2.016 because it has two atoms, and Oxygen would be 16 as it
only has one atom.

The third step is to find the total molecular mass of the molecule.
The molecular mass is the sum of the mass contributions of each
element. For H2O, the molecular mass would be 18.016 because
of the addition of two Hydrogen atoms and one Oxygen atom.

The fourth step is to find the mass percent composition for each
element. To start doing this last step you divide the mass contribution
of each element by the overall total of molecular mass. Then you
multiply by 100 and you get the percent composition by mass of a
specific element in the molecule. In H2O, you can find the percent
composition by mass of Hydrogen by taking the mass of the total of
Hydrogen, 2.016, and dividing it by the total molecular mass of the
molecule, 18.016. The resulting number is .1119. Now you multiply
by 100 and get the percent composition by mass of Hydrogen is 11.2%.
When you do the same for Oxygen such as 16/18.016 equals .88809.
Multiply that by 100 and you get the percent composition 88.8%.

These were all the steps on how to calculate percent composition by mass. It
is an easy process, right? A little hint on how to check if you calculated your
percent composition right is by adding them up and if they do not equal 100
you have to go back and fix it but if they do you are correct with your answers.
I hope you enjoyed learning about the steps. Bye!