Percent Composition - The percent composition of a component in a compound is the percent of the total mass of the compound that is due to that component.

To calculate the percent composition of a component in a compound: Find the molar mass of the compound by adding up the masses of each atom in the compound using the periodic table or a molecular mass calculator.  Calculate the mass due to the component in the compound you are for which you are solving by adding up the mass of these atoms.  Divide the mass due to the component by the total molar mass of the compound and multiply by 100.

Example Percent Composition Problem

Calculate the percent composition of carbon in each of the following:

CO₂

Molar mass of compound: 

Mass due to carbon:   12.01 g/mol

Percent composition of carbon: 

C₆H₁₂O₆

Molar mass of compound: 

Mass due to carbon: 

Percent composition of carbon: 

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