1. 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

2. 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

3. 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 g. What is the molecular formula of ethylene glycol?

4. Empirical Formulas
The empirical formula is thus:
CH3O

5. 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 g H. Determine the empirical formula of the compound.