Chapter 5 Chemical Reactions 5 9 b Molar

Chapter 5 Chemical Reactions 5. 9 b Molar Mass 1

Molar Mass The molar mass • is the mass of one mole of an

Molar Mass from Periodic Table Molar mass is the atomic mass expressed in grams. 1 mole Ag = 107. 9 g 1 mole C = 12. 01 g 1 mole S = 32. 07 g 3

Learning Check Give the molar mass for each (to the tenths decimal place). A. 1 mole K atoms = ____ B. 1 mol Sn atoms = ____ 4

Solution Give the molar mass for each (to the tenths decimal place). A. 1 mole K atoms = 39. 1 g B. 1 mole Sn atoms =118. 7 g 5

Molar Mass of a Compound The molar mass of a compound is the sum of the molar masses of the elements in the formula. Example: Calculate the molar mass of Ca. Cl 2. Element Number of Moles Atomic Mass Total Mass Ca 1 40. 1 g/mole 40. 1 g Cl 2 35. 5 g/mole 71. 0 g Ca. Cl 2 111. 1 g 6

Molar Mass of K 3 PO 4 Calculate the molar mass of K 3 PO 4. Element Number of Moles Atomic Mass Total Mass in K 3 PO 4 K 3 39. 1 g/mole 117. 3 g P 1 31. 0 g/mole 31. 0 g O 4 16. 0 g/mole 64. 0 g K 3 PO 4 212. 3 g 7

Some One-mole Quantities One-Mole Quantities 32. 1 g 55. 9 g 58. 5 g 294. 2 g 342. 2 g 8

Learning Check What is the molar mass of each of the following? A. K 2 O B. Al(OH)3 9

Solution A. K 2 O 94. 2 g/mole 2 mole K (39. 1 g/mole) + 1 mole O (16. 0 g/mole) 78. 2 g + 16. 0 g = 94. 2 g B. Al(OH)3 78. 0 g/mole 1 mole Al (27. 0 g/mole) + 3 mol O (16. 0 g/mole) + 3 mol H (1. 01 g/mole) 27. 0 g + 48. 0 g + 3. 03 g = 78. 0 g 10

Learning Check Prozac, C 17 H 18 F 3 NO, is an antidepressant that inhibits the uptake of serotonin by the brain. What is the molar mass of Prozac? 1) 40. 1 g/mole 2) 262 g/mole 3) 309 g/mole 11

Solution Prozac, C 17 H 18 F 3 NO, is an antidepressant that inhibits the uptake of serotonin by the brain. What is the molar mass of Prozac? 3) 309 g/mole 17 C (12. 0) + 18 H (1. 01) + 3 F (19. 0) + 1 N (14. 0) + 1 O (16. 0) = 204 + 18. 2 + 57. 0 + 14. 0 + 16. 0 = 309 g/mole 12

Molar Mass Factors Molar mass conversion factors • are written from molar mass. • relate grams and moles of an element or compound. Example: Write molar mass factors for methane, CH 4, used in gas stoves and gas heaters. Molar mass: 1 mol CH 4 = 16. 0 g Conversion factors: 16. 0 g CH 4 and 1 mole CH 4 16. 0 g CH 4 13

Learning Check Acetic acid C 2 H 4 O 2 gives the sour taste to vinegar. Write two molar mass conversion factors for acetic acid. 14

Solution Acetic acid C 2 H 4 O 2 gives the sour taste to vinegar. Write two molar mass factors for acetic acid. Calculate molar mass: 24. 0 + 4. 04 + 32. 0 = 60. 0 g/mole 1 mole of acetic acid Molar mass factors 1 mole acetic acid 60. 0 g acetic acid = and 60. 0 g acetic acid 1 mole acetic acid 15

Calculations Using Molar Mass Molar mass factors are used to convert between the grams of a substance and the number of moles. Grams Molar mass factor Moles 16

Moles to Grams Aluminum is often used to build lightweight bicycle frames. How many grams of Al are in 3. 00 mole Al? Molar mass equality: 1 mole Al = 27. 0 g Al Setup with molar mass as a factor: 3. 00 mole Al x 27. 0 g Al 1 mole Al = 81. 0 g Al molar mass factor for Al 17

Learning Check Allyl sulfide C 6 H 10 S is a compound that has the odor of garlic. How many moles of C 6 H 10 S are in 225 g? 18

Solution Calculate the molar mass of C 6 H 10 S. (6 x 12. 0) + (10 x 1. 01) + (1 x 32. 1) = 114. 2 g/mole Set up the calculation using a mole factor. 225 g C 6 H 10 S x 1 mole C 6 H 10 S 114. 2 g C 6 H 10 S molar mass factor (inverted) = 1. 97 mole C 6 H 10 S 19

Grams, Moles, and Particles A molar mass factor and Avogadro’s number convert • grams to particles. molar mass g mole Avogadro’s number particles • particles to grams. Avogadro’s number particles mole molar mass g 20

Learning Check How many H 2 O molecules are in 24. 0 g H 2 O? 1) 4. 52 x 1023 2) 1. 44 x 1025 3) 8. 03 x 1023 21

Solution How many H 2 O molecules are in 24. 0 g H 2 O? 3) 8. 02 x 1023 24. 0 g H 2 O x 1 mole H 2 O x 6. 02 x 1023 H 2 O molecules 18. 0 g H 2 O 1 mole H 2 O = 8. 03 x 1023 H 2 O molecules 22

Learning Check If the odor of C 6 H 10 S can be detected from 2 x 10 -13 g in one liter of air, how many molecules of C 6 H 10 S are present? 23

Solution If the odor of C 6 H 10 S can be detected from 2 x 10 -13 g in one liter of air, how many molecules of C 6 H 10 S are present? 2 x 10 -13 g x 1 mole 114. 2 g x 6. 02 x 1023 molecules 1 mole = 1 x 109 molecules C 6 H 10 S 24