How do you convert between empirical and molecular formulae?

To convert between empirical and molecular formulae, you need to find the ratio of the molecular mass to the empirical formula mass.

The empirical formula of a compound gives the simplest whole-number ratio of atoms of each element in the compound. It is determined by the relative amounts of each element in the compound. For example, the empirical formula of hydrogen peroxide is HO, which tells us that there is one atom of hydrogen for every one atom of oxygen.

The molecular formula, on the other hand, gives the actual number of atoms of each element in a molecule of the compound. For example, the molecular formula of hydrogen peroxide is H2O2, which tells us that there are two atoms of hydrogen and two atoms of oxygen in each molecule.

To convert from the empirical formula to the molecular formula, you need to find the ratio of the molecular mass to the empirical formula mass. This is done by dividing the molecular mass by the empirical formula mass. The result is the number of empirical formula units per molecule. Multiply the subscripts in the empirical formula by this number to get the molecular formula.

For example, the empirical formula of benzene is CH, with a mass of 13 g/mol. The molecular mass of benzene is 78 g/mol. Dividing the molecular mass by the empirical formula mass gives a ratio of 6. Therefore, the molecular formula of benzene is C6H6.

To convert from the molecular formula to the empirical formula, you need to find the greatest common factor of the subscripts in the molecular formula and divide all the subscripts by this number. This will give you the simplest whole-number ratio of atoms, which is the empirical formula.