Calculating Empirical Formulas Chapter 7-3

Empirical Formulas Empirical Formula The Empirical Formula gives the lowest whole number ration of the atoms of the elements in a compound. The empirical formula provides valuable information about the kinds and relative counts of atoms or moles in molecules or formula units of a compound.

Steps to Calculate Empirical Formulas How to calculate empirical formulas? Convert the mass of each element to moles using the molar mass. Divide each mole value by the smallest number of moles calculated. Round to the nearest whole number. This is the mole ratio of the elements and is represented by subscripts in the empirical formula.

Sample Problem What is the empirical formula of a compound that has 25.9 g nitrogen and 88.3 g oxygen? Convert grams to moles 25.9 g N x 1 mol N = 1.85 mol N 14 g N 88.3 g O x 1 mol O = 5.52 mol O 16 g O

Divide each mole by the smallest mole calculated N = = 1 5.52 mol O = = 2.98

Round to the nearest whole number and write the empirical formula. Use the whole numbers to write the empirical formula. Empirical formula = N1O3 Empirical Formula = NO3