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Molecular Formulas You will also be asked to find the molecular formula based on a molecular mass and an empirical formula. This is probably one of the easiest things you will do in this class. The key to this is remembering that the ratio of the masses will always be the same as the ratio of the formulas. If you know the mass ratios, then you automatically know the formula ratio You simply add up the formula weight of the empirical formula and divide it into the molecular mass. This will give you a ratio that you then multiply the empirical formula by. The result is the molecular formula. Examples: .) The molecular mass of the compound for which you found the empirical formula in example a) above is 126.15 grams per mole. What is the molecular formula? The empirical formula in example a) was CH.N, which has a formula mass of: Now divide the molecular mass by the formula mass to get a ratio: 136.155 The ratio is 3, so multiply the empirical formula by 3 to get the molecular formula: Therefore the molecular formula is C,H,N,! b) The molecular mass of the compound whose empirical formula was found in example b) was found to be 164.02 grams per mole. Find the molecular formula. Formula mass of CO.F, is 82.01, so: 164.02 201 (COF) C0,
c) The molecular mass of the compound whose empirical formula was found in example c) was found to be 214.07 grams per mole. Find the molecular formula. Formula mass of Co₂S is 214.07g/mol. Because the formula mass and the molecular mass are the same, the molecular formula is Co₂S, Question 6: Using the empirical formulas you found in 1-5 above, and the molecular masses given, find the molecular formulas. You must show all your work for credit. Please work on a separate piece of paper. 1) 204.93 g/mol 2) 159.69 g/mol 3) 90.03 g/mol 4) 389.42 g/mol 5) 32.06 g/mol