1 Chapter 5 Chemical Reactions and Quantities 5.6 Molar Mass

2 The molar mass is the mass of one mole of an element or compound. is the atomic mass expressed in grams. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

3 Molar Mass from Periodic Table Molar mass is the atomic mass expressed in grams. 1 mole Ag 1 mole C 1 mole S = g = g = g

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

5 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 Solution

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 CaCl 2. ElementNumber of Moles Atomic MassTotal Mass Ca140.1 g/mole 40.1 g Cl235.5 g/mole 71.0 g CaCl g

7 Molar Mass of K 3 PO 4 Calculate the molar mass of K 3 PO 4. ElementNumber of Moles Atomic MassTotal Mass in K 3 PO 4 K339.1 g/mole g P131.0 g/mole 31.0 g O416.0 g/mole 64.0 g K 3 PO g

8 Some One-mole Quantities 32.1 g 55.9 g 58.5 g g g One-Mole Quantities

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

10 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 g = 94.2 g B. Al(OH) 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 g g = 78.0 g Solution

11 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 Learning Check

12 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) = = 309 g/mole Solution

13 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 1 mole CH g CH 4 Molar Mass Factors

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

15 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: = 60.0 g/mole 1 mole of acetic acid = 60.0 g acetic acid Molar mass factors 1 mole acetic acid and 60.0 g acetic acid 60.0 g acetic acid 1 mole acetic acid Solution

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

17 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 = 81.0 g Al 1 mole Al molar mass factor for Al Moles to Grams

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?

19 Calculate the molar mass of C 6 H 10 S. (6 x 12.0) + (10 x 1.01) + (1 x 32.1) = 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 g C 6 H 10 S molar mass factor (inverted) = 1.97 mole C 6 H 10 S Solution

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

21 Learning Check How many H 2 O molecules are in 24.0 g H 2 O? 1) 4.52 x ) 1.44 x ) 8.03 x 10 23

22 Solution How many H 2 O molecules are in 24.0 g H 2 O? 3) 8.02 x g H 2 O x 1 mole H 2 O x 6.02 x H 2 O molecules 18.0 g H 2 O 1 mole H 2 O = 8.03 x H 2 O molecules

23 Learning Check If the odor of C 6 H 10 S can be detected from 2 x g in one 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 g in one liter of air, how many molecules of C 6 H 10 S are present? 2 x g x 1 mole x 6.02 x molecules g 1 mole = 1 x 10 9 molecules C 6 H 10 S