Unit 3 lesson 4

To find the percentage composition of an element in a compound, first find the molar mass of the compound.

Then divide the element mass by the compound mass.

(Think of it this way: What percentage of the total mass of the compound comes from that specific element?)

shows the smallest whole # ratio of atoms in a compound.

For example, the empirical formula of glucose (C6H12O6) would be CH2O.

1st – change % to grams 

2nd – convert grams to moles

3rd – divide all your answers by the smallest # of moles

 indicates the actual # of each type of atom in the compound, and not just their ratios.

most sugars have the simplest formula CH2O; but glucose is C6H12O6 (same ratio, but not exact same formula: CH2O is the simplest formula; C6H12O6 is the molecular formula)

Step 1: Calculate the molar mass of the Empirical Formula

Step 2: Divide the molar mass of the molecular formula over the molar mass of the empirical formula

Your answer is the amount you should multiply your empirical formula's subscripts by