1. Chapter 5 Chemical Reactions and Quantities
5.6
Molar Mass

2. Molar Mass The molar mass
is the mass of one mole of an element or compound.
is the atomic mass expressed in grams.
Copyright © 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 mole C mole S
= g = g = g

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

5. 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 = g

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 CaCl2.
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
CaCl2
111.1 g

7. Molar Mass of K3PO4 Calculate the molar mass of K3PO4. Element
Number of Moles
Atomic Mass
Total Mass in K3PO4 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
K3PO4
212.3 g

8. Some One-mole Quantities
32.1 g g g g g

9. Learning Check What is the molar mass of each of the following? A. K2O
B. Al(OH)3

10. Solution
A. K2O g/mole
2 mole K (39.1 g/mole) + 1 mole O (16.0 g/mole)
78.2 g g = 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 = g

11. Learning Check
Prozac, C17H18F3NO, is an antidepressant that inhibits the uptake of serotonin by the brain. What is the molar mass of Prozac?
1) g/mole
2) 262 g/mole
3) 309 g/mole

12. Solution
Prozac, C17H18F3NO, 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

13. 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, CH4, used in gas stoves and gas heaters.
Molar mass:
1 mol CH4 = g
Conversion factors:
16.0 g CH and mole CH4
1 mole CH g CH4

14. Learning Check
Acetic acid C2H4O2 gives the sour taste to vinegar. Write two molar mass conversion factors for acetic acid.

15. Solution Acetic acid C2H4O2 gives the sour taste to vinegar.
Write two molar mass factors for acetic acid.
Calculate molar mass:
= 60.0 g/mol
1 mole of acetic acid = g acetic acid
Molar mass factors
1 mole acetic acid and g acetic acid
60.0 g acetic acid 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.
Molar mass factor
Moles
Grams

17. 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 = g Al
Setup with molar mass as a factor:
3.00 mole Al x g Al = g Al
1 mole Al
molar mass factor for Al

18. Learning Check
Allyl sulfide C6H10S is a compound that has the odor of garlic. How many moles of C6H10S are in 225 g?

19. Solution Calculate the molar mass of C6H10S.
(6 x 12.0) + (10 x 1.01) + (1 x 32.1) = g/mole
Set up the calculation using a mole factor.
225 g C6H10S x mole C6H10S
114.2 g C6H10S
molar mass factor (inverted)
= 1.97 mole C6H10S

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
particles mole g

21. Learning Check How many H2O molecules are in 24.0 g H2O?
1) x 1023
2) x 1025
3) x 1023

22. Solution How many H2O molecules are in 24.0 g H2O? 3) 8.02 x 1023
24.0 g H2O x 1 mole H2O x 6.02 x 1023 H2O molecules
18.0 g H2O mole H2O
= 8.03 x 1023 H2O molecules

23. Learning Check
If the odor of C6H10S can be detected from 2 x g in one liter of air, how many molecules of C6H10S are present?

24. Solution
If the odor of C6H10S can be detected from 2 x g in one liter of air, how many molecules of C6H10S are present?
2 x g x mole x x 1023 molecules
114.2 g mole
= 1 x 109 molecules C6H10S