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]

Answer:

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