Chapter 9 Problems 9 120 a 9 18

Chapter 9 Problems 9. 120 a, 9. 18 b and 9. 38 a

Citric acid with a molecular mass 192 amu Mass %: C 37. 50, H 4. 21 and O 58. 29 Determine molecular formula starting from 100. 0 g citric acid How many moles of each in 100. 0 g? C: 100. 0 g x 37. 50 g x 1 mole = 3. 122 100. 0 g 12. 01 g H: 100. 0 g x 4. 21 g x 1 mole = 4. 1683 100. 0 g 1. 01 g

Citric acid with a molecular mass 192 amu – cont’d O: 100. 0 g x 58. 29 g x 1 mole = 3. 643 100. 0 g 16. 00 g Empirical formula C: 3. 125/3. 125 = 1 H: 4. 17/3. 125 = 1. 33 O: 3. 643/3. 125 = 1. 166 What is the multiplier? 6

Citric acid with a molecular mass 192 amu – cont’d C 6 Hx. Oy x = 1. 33 * 6 = 7. 98 y = 1. 166 * 6 = 6. 996 C 6 H 8 O 7 This is the …. .

Citric acid with a molecular mass 192 amu – cont’d Empirical formula mass is … 6 * 12. 01 + 8 * 1. 01 + 7 * 16. 00 = 192. 14 amu What is the molecular formula? Same as empirical formula

Citric acid C 6 H 8 O 7 Going Backward Knowing the formula, can we calculate % mass composition? Does it matter if we have empirical or molecular formula?

Problem 9. 18 b) % composition of Na in Na. CN Na: 1 * 22. 99 = 22. 99 amu C: 1 * 12. 01 = 12. 01 amu N: 1 * 14. 01 = 14. 01 amu Total = 49. 01 amu %Na by mass = (22. 99/49. 01) * 100 = 46. 90879%

Problem 9. 38 a) Mass in grams of 0. 981 mole of SO 2 S: 1 * 32. 06 = 32. 06 O: 2 * 16. 00 = 32. 00 Sum = 64. 06 0. 981 mole * (64. 06 g/1 mole) = 62. 84286 g Significant figures? How many molecules of SO 2 in 0. 981 mole?