Skill 8.4 Determining empirical and molecular formulas

If we know the chemical composition of a compound, we can calculate an empirical formula for it. An empirical formula is the simplest formula using the smallest set of integers to express the ratio of atoms present in a molecule. 

To determine an empirical formula from a percent composition, do the following  

3) Divide the values from step 1 by the smallest value to obtain ratios. 

4) Multiply by an integer if necessary to get a whole-number ratio. 

4) Multiply the entire ratio by 2 because you cannot have a fraction of an atom. This corresponds to a ratio of 3 4 2 for an empirical formula of C3H4CI2. 

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