Chapter 5 Chemical Quantities and Reactions 5 2

Chapter 5 Chemical Quantities and Reactions 5. 2 Molar Mass Copyright © 2009 by Pearson Education, Inc. 1

Molar Mass The molar mass is the mass of 1 mole of an element or compound. • is the atomic or molecular mass expressed in grams. • Copyright © 2009 by Pearson Education, Inc. 2

Molar Mass from Periodic Table Molar mass is the atomic mass expressed in grams. 1 mole of Ag = 107. 9 g 1 mole of C = 12. 01 g 1 mole of S = 32. 07 g Copyright © 2009 by Pearson Education, Inc. 3

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

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

Guide to Calculation Molar Mass of a Compound 6

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 7

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 8

Some 1 -mole Quantities One-Mole Quantities 32. 1 g 55. 9 g 58. 5 g 294. 2 g 342. 2 g Copyright © 2009 by Pearson Education, Inc. 9

Learning Check What is the molar mass of each of the following? A. K 2 O B. Al(OH)3 10

Solution A. K 2 O 94. 2 g/mole 2 moles of K (39. 1 g/mole) + 1 mole of O (16. 0 g/mole) 78. 2 g + 16. 0 g = 94. 2 g B. Al(OH)3 78. 0 g/mole 1 mole of Al (27. 0 g/mole) + 3 moles of O (16. 0 g/mole) + 3 moles of H (1. 01 g/mole) 27. 0 g + 48. 0 g + 3. 03 g = 78. 0 g 11

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 12

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 g C + 18. 2 g H + 57. 0 g F + 14. 0 g N + 16. 0 g O = 309 g/mole 13

Molar Mass Factors Molar mass conversion factors • are fractions (ratios) written from the molar mass. • relate grams and moles of an element or compound. • for methane, CH 4, used in gas stoves and gas heaters is 1 mole of CH 4 = 16. 0 g (molar mass equality) Conversion factors: 16. 0 g CH 4 and 1 mole CH 4 16. 0 g CH 4 14

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. Copyright © 2009 by Pearson Education, Inc. 15

Solution Calculate molar mass for acetic acid C 2 H 4 O 2: 24. 0 g C + 4. 04 g H + 32. 0 g O = 60. 0 g/mole C 2 H 4 O 2 1 mole of acetic acid Molar mass factors: 1 mole acetic acid 60. 0 g acetic acid = 60. 0 g acetic acid and 60. 0 g acetic acid 1 mole acetic acid 16

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 17

Moles to Grams Aluminum is often used to build lightweight bicycle frames. How many grams of Al are in 3. 00 mole of Al? Molar mass equality: 1 mole of Al = 27. 0 g of Al Setup with molar mass as a factor: 3. 00 mole Al x 27. 0 g Al 1 mole Al = 81. 0 g of Al molar mass factor for Al 18

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? Copyright © 2009 by Pearson Education, Inc. 19

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 moles of C 6 H 10 S 20

Grams, Moles, and Particles A molar mass factor and Avogadro’s number convert… 21

Learning Check How many H 2 O molecules are in 24. 0 g of H 2 O? 1) 4. 52 x 1023 H 2 O molecules 2) 1. 44 x 1025 H 2 O molecules 3) 8. 03 x 1023 H 2 O molecules 22

Solution How many H 2 O molecules are in 24. 0 g of 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 23

Learning Check If the odor of C 6 H 10 S can be detected from 2 x 10 -13 g in 1 liter of air, how many molecules of C 6 H 10 S are present? 24

Solution If the odor of C 6 H 10 S can be detected from 2 x 10 -13 g in 1 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 of C 6 H 10 S are present 25