The formula for percent composition is the individual mass of a specific component over the total molar mass of the compound times 100 percent, notes the Department of Chemistry at Texas A&M University. This formula allows students to find the percent mass of one atom in a compound.
Use the molecular formula of a compound to calculate percent composition. Determine the molar mass of the entire compound to calculate percent mass. Next, find the molar mass of each atom in the compound. Divide each individual atom’s molar mass by the total compound’s molar mass to determine the fractional value of each atom in the compound. Then, multiply the fractional values by 100 to determine the percent mass of each atom in a compound, according to Texas A&M University.