How to Find the Percent Composition by Mass for Sodium sulfate (Na2SO4)

To find the percent composition (by mass) for each element in Na2SO4 we need to determine the molar mass for each element and for the entire Na2SO4 compound.

We’ll use the following formula for percent composition by mass:

Percent Composition by Mass = (Molar Mass of Element x Number of that Element)/ Molar Mass of Compound

In this video I’m using a Periodic Table that rounds to two decimal places. You may be asked to use a Periodic Table with more decimal places, however the process to find the percent composition by mass for Na2SO4 is the same.

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Note that if you add up the percentages for all of the elements it should be close to 100%. Often it will not be exact to the rounding of the atomic mass for elements.

Note: Na2SO4 is also known as Sodium sulfate.