Chemical Formulae

Chemical Formulae are a way of representing the chemical structure of a molecule or compound.

Empirical Formulae

Simplest whole number ratio in which elements combine.
e.g. CH

Molecular Formulae

Number of atoms of each element of each type per molecule.
e.g. C2H2

Determining Empirical and Molecular Formulae

  • When given the % compositions just take the percentage, treat as grams in a 100gm substance and then determine the moles.
  • The number of moles can then be compared to figure out the ratios for the empirical formula.

To calculate the molecular formula, once given a weight:

  • Divide the moles for each component by 100gm and multiply by the given mass.
  • Hence the number of moles per component.