Empirical Formulas formaldehyde CH2O (toxic preservative) acetic acid C2H4O2 (vinegar) glucose C6H12O6 (simple sugar) all have the same basic or “empirical” formula CH2O

empirical formula: the smallest whole-number ratio of the atoms in a compound. Examples: CH3 HO PbO2 C2H6N Non-Examples: C2H6 H2O2 Pb2O4 C6H18N3

Acetylene (C2H2) is a gas used in welder’s torches. These two compounds of carbon both have the same empirical formula (CH) but different molecular formulas. Styrene (C8H8) is used in making polystyrene.

Percent to Mass Mass to Mole Divide by Small Times ‘till Whole What is the empirical formula of a compound that is analyzed and found to contain 25.9% N and 74.1% O? Percent to Mass Mass to Mole Divide by Small Times ‘till Whole

What is the empirical formula of a compound that is analyzed and found to contain 25.9% N and 74.1% O? Percent to Mass Mass to Mole Divide by Small Times ‘till Whole 25.9 g N 74.1 g O x 1 mol N 14.01 g N x 1 mol O 16.00 g O = 1.85 mol N = 4.63 mol O ________ 1.85 = 1 N = 2.5 O x 2 = 2 N x 2 = 5 O N2O5

1,6-diaminohexane is used to make nylon 1,6-diaminohexane is used to make nylon. What is the empirical formula if it is 62.1% C, 13.8% H, and 24.1% N? 62.1 g C 13.8 g H 24.1 g N x 1 mol C 12.01 g C x 1 mol H 1.01 g H x 1 mol N 14.01 g N = 5.17 mol C = 13.66 mol H = 1.72 mol N ________ 1.72 _________ = 3 C = 8 H = 1 N C3H8N

molecular formula: a whole-number multiple of the empirical formula of a compound formaldehyde CH2O acetic acid C2H4O2 glucose C6H12O6 all have the same empirical formula CH2O

Calculate the molecular formula of a compound with the empirical formula CH4N and a molar mass of 60.0 g/mol. molecular mass = multiple of emp. form. empirical mass empirical mass 1(C) + 4(H) + 1(N) = 12.01 + 4(1.01) + 14.01 = 30.06 g/mol 60.0 = 30.06 1.996 ≈ 2 2 (CH4N) = C2H8N2

Calculate the molecular formula of benzene with the empirical formula CH and a molar mass of 78 g/mol. molecular mass = multiple of emp. form. empirical mass empirical mass 1(C) + 1(H) = 12.01 + 1.01 = 13.02 g/mol 78 = 13.02 5.991 ≈ 6 6 (CH) = C6H6

Quick Quiz! 1. An empirical formula shows the __________ of atoms in a compound. lowest common number highest whole ratio lowest whole number ratio average ratio

Quick Quiz. 2. Which of the following is NOT an empirical formula? CH3 H2N CH C3H6

Quick Quiz. 3. True or False: A molecular formula can be the same as an empirical formula. True False Example: Formaldehyde has the empirical formula CH2O, which is its molecular formula as well.

Quick Quiz. 4. Determine the molecular formula of a compound that contains 40.0 % C, 6.71 % H, and 53.29 % O by mass and has a molar mass of 60.05 g/mol. C2H4O2 CH2O C2H3O C2H4O