1. Chapter 6 Chemical Reactions and Quantities
6.5 Molar Mass

2. Molar Mass The molar mass is the mass of one mole of a substance
the atomic mass of an element expressed in grams

3. Learning Check Give the molar mass to the nearest 0.1 g.
A. K = ________
B. Sn = ________

4. Solution Give the molar mass to the nearest 0.1 g. A. K = 39.1 g
B. Sn = g

5. Molar Mass of CaCl2
For a compound, the molar mass is the sum of the molar masses of the elements in the formula. We calculate the molar mass of CaCl2 to the nearest 0.1 g as follows.
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

6. Molar Mass of K3PO4 Determine the molar mass of K3PO4 to 0.1 g. K 3
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

7. One-Mole Quantities
32.1 g g g g g

8. Guide to Calculating Molar Mass

9. Learning Check
Calculate the molar mass for Al(OH)3 to the nearest 0.1g.
1) g/mole
2) g/mole
3) g/mole

10. Solution
STEP 1 Obtain the molar mass of each element Al g/mole O g/mole
H g/mole
STEP 2 Multiply each by the subscript in the formula.
1 mole Al x g Al = g
1 mole Al
3 moles O x g O = g
1 mole O
3 moles H x 1.0 g H = g
1 mole H
STEP 3 Total: 1 mole of Al(OH)3 = g (3)

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
3) 309 g/mole
STEP 1 Obtain the molar mass of each element C g/mole H 1.0 g/mole
F g/mole N 14.0 g/mole O 16.0 g/mole
STEP 2 Multiply each by the subscript in the formula.
17 moles C x g C = g
1 mole C
18 moles H x 1.0 g H = g
1 mole H

13. Solution (continued) STEP 2 (continued) 3 moles F x 19.0 g F = 57.0 g
1 mole F
1 mole N x g N = g
1 mole N
1 mole O x g O = g
1 mole O
STEP 3 Total: 1 mole of C17H18F3NO = g

14. Conversion Factors from Molar Mass
Methane (CH4), known as natural gas, is used in gas stoves and gas heaters.
1 mole of CH4 = g of CH4
The molar mass of methane can be written as conversion factors.
16.0 g CH and mole CH4
1 mole CH g CH4

15. Learning Check Acetic acid, C2H4O2, gives the sour taste to vinegar.
Write an equality and two molar mass conversion factors for acetic acid.

16. Solution Acetic acid, C2H4O2, gives the sour taste to vinegar.
Write an equality and two molar mass conversion factors for acetic acid.
Equality:
1 mole of acetic acid = g of acetic acid
Molar mass conversion factors:
1 mole acetic acid and g acetic acid
60.0 g acetic acid mole acetic acid

17. Guide to Calculations Using Molar Mass

18. Calculating Grams from Moles
Aluminum is often used for the structure of lightweight bicycle frames. How many grams of Al are in 3.00 moles of Al?
3.00 moles Al x g Al = g of Al
1 mole Al
mole factor for Al

19. Learning Check
The artificial sweetener aspartame (NutraSweet), C14H18N2O5 , is used to sweeten diet foods, coffee, and soft drinks. How many moles of aspartame are present in 225 g of aspartame?

20. Solution STEP 1 Given: 225 g of aspartame, C14H18N2O5
STEP 2 Plan: g of aspartame moles of aspartame
STEP 3 Determine molar mass of aspartame:
14(12.0) + 18(1.0) + 2(14.0) + 5(16.0)
= 294 g/mole
STEP 4 Set up problem to calculate the moles of aspartame:
225 g aspartame x 1 mole aspartame
294 g aspartame
mole factor (inverted)
= mole of aspartame

21. Converting Between Mass, Moles, and Particles