Empirical Formula

Empirical Formula

1. The empirical formula of a substance is the chemical formula that gives the simplest whole-number ratio of atoms of each element in the substance.
2. Empirical = information gained by means of observation, experience, or experiment.

Example:

 Chemical Substances Molecular Formula Empirical Formula Glucose C6H12O6 CH2O Water H2O H2O Carbon Dioxide CO2 CO2 Benzene C6H6 CH Butane C4H8 CH2

Finding Empirical Formula

Steps to determine the empirical formula of a compound
STEP 1: Find the mass
STEP 2: Find the mole
STEP 3: Find the simplest ratio

Example:
In a chemical reaction, 4.23g of iron reacts completely with 1.80g of oxygen gas, producing iron oxide. Calculate the empirical formula of iron oxide. [Relative atomic mass: Iron = 56; Oxygen = 16]

 Element Fe O Mass 4.23g 1.80g Number of mole 4.23/56 =0.0755 1.80/16 =0.1125 Simple ratio 0.0755/0.0755 =1 0.1125/0.0755 =1.5 Ratio in round number 2 3

The empirical formula of iron oxide = Fe2O3

Example:
Determine the empirical formula of a compound which has a percentage of composition Mg: 20.2%, S: 26.6%, O: 53.2%. [Relative atomic mass: Mg = 24; S = 32; O = 16]