1. Moles and Stoichiometry Chemical Reactions and Quantities
Molar Mass
Gram Formula Mass

2. Molar Mass The molar mass or gram formula mass
is the mass in grams, of one mole of an element or compound.
is the atomic mass expressed in grams.
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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. Solution
Caffeine, the compound that basically keeps Mrs. Mannion alive, has the following formula: C8H10N4O2. What is the gram formula mass of Caffeine?

12. Learning Check
Caffeine, the compound that basically keeps Mrs. Mannion alive, has the following formula: C8H10N4O2. What is the gram formula mass of Caffeine?
C : 8 x 12.0 = 96.0
H: 10 x 1.0 = 10.0
N: 4 x 14.0 = 56.0
O: 2 x 16.0 = 32.0
194.0 g

13. Learning Check
Prozac, C17H18F3NO, is an SSRI category of antidepressant that inhibits the re-uptake of serotonin by the brain. What is the molar mass of Prozac?

14. 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

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

16. 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
= 1.97 mole C6H10S

17. 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

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

19. 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

20. 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?

21. 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

22. Moles and Volume
For gases, there is another component relating volume and moles
1 mole of any substance takes up 22.4 liters of space
1 mole = 22.4 L of gas, no matter what the gas is, or what the formula mass of that gas may be

23. Example
A sample of O2 takes up 33.6L. How many moles are present in the sample?
Solution:
33.6L x 1 mole = 1.5 moles
22.4L

24. Example
A sample of NH3 contains 3 moles. What is the volume of that gas? Solution: 3 moles NH3 x 22.4 L = 67.2 L 1 mole

25. Volume and Particles A sample of helium gas occupies11.2 liters.
How many particles are in the sample?
(are these particles atoms or molecules, and why?)

26. Volume and Particles
A sample of NH3 occupies 7.5 L. How many particles are in the sample?
(Are these particles atoms or molecules, and why?)

27. Summary