1. Empirical Formulas, Hydrates, and Molecular Formulas
Chapter 7: p

2. Molecular Formulas Empirical Formula
A chemical formula that shows the actual number and kinds of atoms present in a molecule
Empirical Formula
A formula representing the lowest whole number ratio of atoms of the elements in a compound
An empirical formula may or may not be the same as the molecular formula

3. Calculating Empirical Formulas:
Steps:
If given %, assume 100g of sample (%  g)
Calculate the number of moles of each element
Divide results of #2 by the smallest number of moles
If the ratios are not whole #s, find and multiply by a # that will give whole #s
Write the empirical formula! 

4. Example #1
A: N2O5
Calculate the empirical formula if the compound is made up of: 25.9% Nitrogen and 74.1% Oxygen

5. Example #2
A: HgSO4
Calculate the empirical formula if the compound is made up of: 67.6% Hg, 10.8% S, and 21.6% O

6. Example #3
A: Sr3P2O8  Sr3(PO4)2
Calculate the empirical formula if the compound is made up of: 57.6% Sr, 13.8% P, and 28.6% O

7. Calculating Molecular Formulas:
Steps:
Calculate the molar mass of the empirical formula
Divide the empirical molar mass into the molecular molar mass
Multiply the empirical formula by the whole number that you calculated in step #2