Determination of Empirical and molecular formulae:- the following steps are followed to determine the empirical formula of the compound.
(i)          The percentage composition of the compound is determined by quantitative analysis.
 

(ii)         The percentage of each element is divided by its atomic mass. It gives atomic ration of the elements present in the compound.
 

(iii)        The atomic ratio of each element is divided by the atoms of elements present in the compound. 
 

(iv)       If the simplest ratio is fractional, then a value of simplest ratio of each element is multiplied by smallest integers to get a simplest whole number of each of the element.
 

(v)         To get the empirical formula, symbols of various elements present are written side by side with their respective whole number ratio as a subscript to the lower right hand corner of the symbol.
The molecular formula of a substance may be determined from the empirical formula if the molecular mass of the substances is known. The molecular formula is always a simple multiple of empirical formula and the value of simple multiple is obtained by dividing molecular mass with empirical formula mass.