% Element = (n × atomic mass / molar mass) × 100
Percent composition tells you the mass percentage of each element in a compound. For element X: % X = (number of X atoms × atomic mass of X / molar mass of compound) × 100. Example: glucose C₆H₁₂O₆ (MW = 180.16): %C = 6×12.011/180.16 = 40.00%, %H = 12×1.008/180.16 = 6.71%, %O = 6×16.00/180.16 = 53.29%. The percentages must sum to 100%. Percent composition is used to: verify compound identity, determine empirical formulas from experimental data, calculate the mass of a specific element in a given mass of compound, and assess the nutritional or economic value of minerals and ores. In reverse, percent composition data from combustion analysis leads to empirical formulas.