Empirical Formula

The empirical formula represents the simplest formula for a compound. 

Examining Empirical Formulas

Concept: Empirical Formula vs. Molecular Formula


Example: What is the empirical formula of dimethylhydrazine, C2HN2, a colorless liquid used as a rocket fuel? 


The empirical formula represents the lowest ratio of moles of each element within the compound. 

Example: Elemental analysis of a sample of an ionic compound showed 2.82 g of Na, 4.35 g of Cl, and 7.83 g of O. What is the empirical formula and name of the compound?


Whenever you are given the mass or percentages of elements you can assume it is out of 100 grams. 

Example: After a workout session, lactic acid (M = 90.08 g/mol) forms in muscle tissue and is responsible for muscle soreness. Elemental analysis shows that this compound contains 40% C, 6.7% H and 53.3% O. Determine the molecular formula. 


Combustion Analysis

Combustion analysis is a technique where an organic compound is combusted (exploded!!!) and the products are quantitatively measured. 

In a combustion reaction the organic compound is combusted to form carbon dioxide and water as products. 

Example: A 0.2500 g sample contains carbon, hydrogen and oxygen and undergoes complete combustion to produce 0.3664 g of CO2 and 0.1500 g of H2O. What is the empirical formula of the compound?