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Empirical Formulas

Empirical Formulas. formaldehyde CH 2 O (toxic preservative) acetic acid C 2 H 4 O 2 (vinegar) glucose C 6 H 12 O 6 (simple sugar) all have the same basic or “ empirical ” formula CH 2 O. empirical formula : the smallest whole-number ratio of the atoms in a compound.

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Empirical Formulas

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

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

  3. 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.

  4. 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

  5. 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 N = 2.5 O x 2 = 2 N x 2 = 5 O ________ 1.85 ________ 1.85 N2O5

  6. 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 = 3C = 8H = 1N ________ 1.72 _________ 1.72 ________ 1.72 C3H8N

  7. molecular formula: • awhole-number multiple of the empirical formulaof a compound formaldehyde CH2O acetic acid C2H4O2 glucose C6H12O6 all have the same empirical formula CH2O

  8. 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

  9. 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

  10. 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

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

  12. 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.

  13. 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

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