INTRODUCTION Chemical formulas indicate the composition of compounds. A formula that gives only the simplest ratio of the relative number of atoms in a compound is the empirical formula or simplest formula. The ratio usually consists of small whole numbers. We call a formula that gives the actual numbers of each type of atom in a compound the molecular formula. The numbers in a molecular formula will be whole number multiples of the numbers in an empirical formula. To determine the molecular formula of a compound, we need to know both the empirical formula and the molar mass of the compound. Benzene, for example, has an empirical formula of CH. In a molecule of benzene, the number of carbon atoms (C) and hydrogen atoms (H) are the same. The molar mass of benzene is 78.11 g/mol. We can determine the molecular formula of benzene by first calculating the molar mass of the empirical formula, which is 13.02 g/mol. We then determine the number of empirical units in a molecule by dividing the molar mass of benzene by the empirical molar mass: Number of empirical units = (78.11 g/mol) / (13.02 g/mol) = 6 empirical units Multiplying the empirical formula by 6 gives the molecular formula of benzene, (CH) X 6 or C6H6. Experimentally, we can determine the empirical formula of a compound by first finding the mass of each element in a sample of the compound. We then convert the mass of each element to the equivalent number of moles of that element. To find the simplest formula of a compound, we will combine the elements in the compound under conditions that allow us to determine the mass of each element. From these data, the moles of atoms of each element may be calculated. By dividing the numbers to the smallest number of moles, you obtain quotients that are in a simple ratio of integers or are readily converted to such a ratio. The ratio of moles of atoms of the elements in a compound is the same as the ratio of individual atoms…
