Empirical Formulas formaldehyde CH 2 O toxic preservative

Empirical Formulas formaldehyde CH 2 O (toxic preservative) acetic acid (vinegar) C 2 H 4 O 2 glucose C 6 H 12 O 6 (simple sugar) all have the same basic or “empirical” formula CH 2 O © Copyright Pearson Prentice Hall Slide 1 of 40 End Show

Percent Composition and Chemical Formulas > empirical formula: the smallest whole-number ratio of the atoms in a compound. Examples: CH 3 HO Pb. O 2 C 2 H 6 N Pb 2 O 4 C 6 H 18 N 3 Non-Examples: C 2 H 6 H 2 O 2 © Copyright Pearson Prentice Hall Slide 2 of 40 End Show

Percent Composition and Chemical Formulas > Acetylene (C 2 H 2) 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 (C 8 H 8) is used in making polystyrene. © Copyright Pearson Prentice Hall Slide 3 of 40 End Show

SAMPLE PROBLEM 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 to Mole Divide by Small Times ‘till Whole © Copyright Pearson Prentice Hall Slide 4 of 40 End Show

SAMPLE PROBLEM 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 to Mole Divide by Small Times ‘till Whole 25. 9 g N x 1 mol N = 1. 85 mol N = 1 N ____ 14. 01 g N 1. 85 x 2=2 N 74. 1 g O x 1 mol O = 4. 63 mol O = 2. 5 O x 2 = 5 O ____ 16. 00 g O Slide 1. 85 5 of 40 © Copyright Pearson Prentice Hall N 2 OEnd 5 Show

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? Practice Problems 62. 1 g C x 1 mol C = 5. 17 mol C ____ 12. 01 g C 1. 72 = 3 C 13. 8 g H x 1 mol H = 13. 66 mol H = 8 H _____ 1. 01 g H 1. 72 24. 1 g N x 1 mol N = 1. 72 mol N ____ 14. 01 g N 1. 72 © Copyright Pearson Prentice Hall = 1 N C 3 H 8 N Slide 6 of 40 End Show

Percent Composition and Chemical Formulas > molecular formula: a whole-number multiple of the empirical formula of a compound formaldehyde CH 2 O acetic acid C 2 H 4 O 2 glucose C 6 H 12 O 6 all have the same empirical formula CH 2 O © Copyright Pearson Prentice Hall Slide 7 of 40 End Show

SAMPLE PROBLEM Calculate the molecular formula of a compound with the empirical formula CH 4 N and a molar mass of 60. 0 g/mol. molecular mass = multiple of emp. form. empirical mass 1(C) + 4(H) + 1(N) = 12. 01 + 4(1. 01) + 14. 01 = 30. 06 g/mol 60. 0 = 1. 996 ≈ 2 30. 06 2 (CH 4 N) = © Copyright Pearson Prentice Hall C 2 H 8 N 2 Slide 8 of 40 End Show

SAMPLE PROBLEM 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 1(C) + 1(H) = 12. 01 + 1. 01 = 13. 02 g/mol 78 = 5. 991 ≈ 6 13. 02 6 (CH) = © Copyright Pearson Prentice Hall C 6 H 6 Slide 9 of 40 End Show

Quick Quiz! 1. An empirical formula shows the _____ of atoms in a compound. A. lowest common number B. highest whole ratio C. lowest whole number ratio D. average ratio

Quick Quiz. 2. Which of the following is NOT an empirical formula? A. CH 3 B. H 2 N C. CH D. C 3 H 6

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 CH 2 O, 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. A. C 2 H 4 O 2 B. CH 2 O C. C 2 H 3 O D. C 2 H 4 O