Empirical Formula

Some Basic Concept Of Chemistry of Class 11

 Empirical Formula

The formula which express the smallest whole number ratio of the constituent atom within the molecule. Empirical formula of different compound may be same. So it may or may not represent the actual formula of the molecule. It can be deduced by knowing the weight % of all the constituent element with their atomic masses for the given compound.

For example: C6H12O6, CH3COOH, HCHO

All has same empirical formula CH2O but they are different.

The empirical formula of a compound can be determined by the following steps:

  • Write the name of detected elements in column-1 present in the compound.
  • Write the corresponding atomic mass in column-2.
  • Write the experimentally determined percentage composition by weight of each element present in the compound in column-3.
  • Divide the percentage of each element by its atomic weight to get the relative number of atoms of each element in column-4.
  • Divide each number obtained for the respective elements in step (3) by the smallest number among those numbers so as to get the simplest ratio in column-5.
  • If any number obtained in step (4) is not a whole number then multiply all the numbers by a suitable integer to get whole number ratio. This ratio will be the simplest ratio of the atoms of different elements present in the compound. Empirical formula of the compound can be written with the help of this ratio in column-6.
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