Percent Composition -percent composition is the percentage of a particular element in a compound -this can be useful for further understanding stoichiometric relationships and determining what a new substance is

Empirical Formulas -an empirical formula is the formula for a compound with the simplest subscripts possible Ex: C6H12O6 becomes CH2O CH2O stays as CH2O B2H6 becomes BH3 BF3 stays as BF3 -to determine the empirical formula with percentages, use percentages to find moles of compound by dividing each by molar mass -then, to find the relative molar ratios, divide each by the smallest mole number

Empirical Formulas Example The compound ethylene glycol is often used as an antifreeze. It contains 38.7% carbon, 9.75% hydrogen, and the rest oxygen. The molecular weight of ethylene glycol is 62.07 g. What is the molecular formula of ethylene glycol?

Empirical Formulas The empirical formula is thus: CH3O

Significant Figures Practice Find the percent composition of each element in Ca(OH)2. A compound was analyzed and found to contain 13.5 g Ca, 10.8 g O, and 0.675 g H. Determine the empirical formula of the compound.