Empirical Formula
Key Stage 4
Meaning
An empirical formula is the simplest ratio of the different types of atom in a compound.
About Empirical Formulae
The empirical formula of a compound may not be the same as the chemical formula:
- Ethane - Chemical Formula C2H6, Empirical Formula CH3
- Ethene - Chemical Formula C2H4, Empirical Formula CH2
- Propene - Chemical Formula C3H6, Empirical Formula CH2
- Glucose - Chemical Formula C6H12O6, Empirical Formula CH2O
- Lactic Acid - Chemical Formula C3H6O3, Empirical Formula CH2O
- Empirical formulae are calculated from the amount of atoms in a chemical reaction.
- The number of atoms can be found if you know the mass of different elements and the relative atomic mass of the elements in the reaction.
Finding the Empirical Formula
| Number of Atoms | Picture | Structural Diagram |
| 100 atoms of Hydrogen react completely with 50 atoms of Oxygen. |  |
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The ratio of Hydrogen atoms to Oxygen atoms H:O 100:50 2:1 So the empirical formula is H2O |
In this diagram there are 4 Carbon atoms, 10 Hydrogen atoms. C:H 4:10 2:5 So the empirical formula is C2H5 |
In this diagram there are 4 Carbon atoms, 10 Hydrogen atoms and 2 Oxygen atoms. C:H:O 4:10:2 2:5:1 So the empirical formula is C2H5O
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