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General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 1
Chapter 6 Chemical Reactions and Quantities
6.5Molar Mass
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 2
The molar mass is the mass of one mole
of a substance the atomic mass of an
element expressed in grams
Molar Mass
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 3
Give the molar mass to the nearest 0.1 g.
A. K = ________
B. Sn = ________
Learning Check
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 4
Give the molar mass to the nearest 0.1 g.
A. K = 39.1 g
B. Sn = 118.7 g
Solution
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 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 1 111.1 g
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 6
Molar Mass of K3PO4
Determine the molar mass of K3PO4 to 0.1 g.
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 1 212.3 g
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 7
One-Mole Quantities
32.1 g 55.9 g 58.5 g 294.2 g 342.3 g
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.
Guide to Calculating Molar Mass
8
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 9
Calculate the molar mass for Al(OH)3 to the nearest 0.1g.
1) 44.0 g/mole
2) 75.0 g/mole
3) 78.0 g/mole
Learning Check
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 10
STEP 1 Obtain the molar mass of each element. Al 27.0 g/mole O 16.0 g/mole
H 1.0 g/moleSTEP 2 Multiply each by the subscript in the formula.
1 mole Al x 27.0 g Al = 27.0 g 1 mole Al
3 moles O x 16.0 g O = 48.0 g 1 mole O
3 moles H x 1.0 g H = 3.0 g 1 mole H STEP 3 Total: 1 mole of Al(OH)3 = 78.0 g (3)
Solution
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 11
Prozac, C17H18F3NO, is an antidepressant that inhibits the uptake of serotonin by the brain. What is the molar mass of Prozac?
1) 40.0 g/mole
2) 262 g/mole
3) 309 g/mole
Learning Check
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 12
3) 309 g/mole
STEP 1 Obtain the molar mass of each element. C 12.0 g/mole H 1.0 g/mole
F 19.0 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 12.0 g C = 204 g
1 mole C 18 moles H x 1.0 g H = 18 g
1 mole H
Solution
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 13
STEP 2 (continued) 3 moles F x 19.0 g F = 57.0 g
1 mole F 1 mole N x 14.0 g N = 14.0 g
1 mole N
1 mole O x 16.0 g O = 16.0 g 1 mole O
STEP 3 Total: 1 mole of C17H18F3NO = 309 g
Solution (continued)
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 14
Methane (CH4), known as natural gas, is used in gas stoves and gas heaters.
1 mole of CH4 = 16.0 g of CH4
The molar mass of methane can be written as conversion factors.
16.0 g CH4 and 1 mole CH4
1 mole CH4 16.0 g CH4
Conversion Factors from Molar Mass
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 15
Acetic acid, C2H4O2, gives the sour taste to vinegar.
Write an equality and two molar mass conversion factors for acetic acid.
Learning Check
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 16
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 = 60.0 g of acetic acid
Molar mass conversion factors:
1 mole acetic acid and 60.0 g acetic acid
60.0 g acetic acid 1 mole acetic acid
Solution
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 17
Guide to Calculations Using Molar Mass
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 18
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 27.0 g Al = 81.0 g of Al1 mole Al
mole factor for Al
Calculating Grams from Moles
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 19
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?
Learning Check
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 20
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)
= 0.765 mole of aspartame
Solution
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.
Converting Between Mass, Moles, and Particles
21