Define the term empirical formula. Determine the molecular formula of a compound with the empirical formula C2H4O and a relative molecular mass of 176.0
Empirical formula is the simplest whole number ratio of atoms of each element in a compound. With the empirical formula and relative molecular mass, we can determine the actual molecular formula of a compound (which is the actual whole number of atoms of each element in the compound).
To determine the molecular formula of a compound, we first have to calculate the Mr (molecular mass) of the empirical formula. Looking at the periodic table, we can see the relative atomic mass of each element (the Ar) - carbon is 12.0, hydrogen is 1.0 and oxygen is 16.0. As the empirical formula is C2H4O we have to take into account the number of each element in this molecule - therefore we do the following calculation; (2 x 12.0) + (4 x 1.0) + (1 x 16.0) = 44.0 - because the molecule contains 2 atoms of carbon, 4 atoms of hydrogen and 1 of oxygen.Now that we have calculated the Mr of the C2H4O, we can divide the given relative molecular mass of 176.0 by 44.0 to find the ratio. 176.0/44.0 = 4. We therefore know that the Mr of the compound is 4 times the Mr of the simplest whole number ratio; the compound we have been asked to find is therefore C8H16O4
