Calculating Empirical and Molecular Formula

Calculating Empirical Formula

1.        Find the mass of each element in the compound. In order to do this, you must assume that you have 100g of the compound (this allow for percentage values too be converted to grams).
2.        Using the mass values from step 1, calculate the number of moles of each element in the compound (using the formula n = m/M).
3.        Put the number of moles of each element into a ratio statement. Divide all of the mole values by the lowest number (this will give you the subscript values for the empirical formula). If there are numbers with decimals, multiply all of the subscripts by 2, 3, or 4 to get whole numbers (do not put decimals into the final answer of the empirical formula.

Calculating True Molecular Formula

1.        Find the empirical formula
2.        Find the empirical formula molar mass
3.        Divide the molecular mass by the empirical mass
4.        Multiply each subscript by the answer from step three