Introduction: Percent composition by mass refers to the percentage by mass of an element that exists in a compound. Percent composition by mass is an important concept in chemistry, because it helps us to understand and visualize the mass of atoms of elements in nature. Percent composition by mass is used in many applications relating to industry, pharmacy, and construction. The formula for percent composition by mass is written as follows:

[math]"Percent Composition By Mass of Element X" = "Mass of Element X" / "Mass of One Mole of Compound" xx 100%[/math]

Percent composition by mass is used in jewelry to determine the correct percentage of a specific metal in an alloy (a mixture of metals). Percent composition is also used to determine the correct amount of specific elements in a mixture of concrete, as well as to determine the correct amount of an element or mineral in specific pharmaceuticals. Yet another, more practical application is to determine the amount of water in a mixture of Kool-Aid - the amounts of water in a mixture of Kool-Aid can make all the difference between a sweet mixture of Kool-Aid and a bitter mixture of Kool-Aid.