Transcript 5.2 Molar Mass

Chapter 5
Chemical Quantities and Reactions
5.2
Molar Mass
Copyright © 2009 by Pearson Education, Inc.
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Molar Mass
The molar mass
• is the mass of 1 mole of
an element or
compound.
• is the atomic or
molecular mass
expressed in grams.
Copyright © 2009 by Pearson Education, Inc.
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Molar Mass from Periodic Table
Molar mass
is the atomic
mass
expressed in
grams.
1 mole of Ag
= 107.9 g
1 mole of C
= 12.01 g
1 mole of S
= 32.07 g
Copyright © 2009 by Pearson Education, Inc.
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Learning Check
Give the molar mass for each (to the tenths decimal
place).
A. 1 mole of K atoms =
________
B. 1 mole of Sn atoms =
________
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Solution
Give the molar mass for each (to the tenths decimal
place).
A.
1 mole of K atoms
=
B.
1 mole of Sn atoms =
39.1 g
118.7 g
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Guide to Calculation Molar Mass of
a Compound
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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
Atomic Mass Total Mass
Ca
Number
of Moles
1
40.1 g/mole
40.1 g
Cl
2
35.5 g/mole
71.0 g
CaCl2
111.1 g
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Molar Mass of K3PO4
Calculate the molar mass of K3PO4.
Element Number
of Moles
K
3
Atomic Mass
P
1
31.0 g/mole
31.0 g
O
4
16.0 g/mole
64.0 g
K3PO4
39.1 g/mole
Total Mass
in K3PO4
117.3 g
212.3 g
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Some 1-mole Quantities
One-Mole Quantities
32.1 g
55.9 g
58.5 g
294.2 g
342.2 g
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Learning Check
What is the molar mass of each of the following?
A. K2O
B. Al(OH)3
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Solution
A. K2O 94.2 g/mole
2 moles of K (39.1 g/mole) + 1 mole of O (16.0 g/mole)
78.2 g + 16.0 g = 94.2 g
B. Al(OH)3 78.0 g/mole
1 mole of Al (27.0 g/mole) + 3 moles of O (16.0 g/mole)
+ 3 moles of H (1.01 g/mole)
27.0 g + 48.0 g + 3.03 g = 78.0 g
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Learning Check
Prozac, C17H18F3NO, 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
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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) =
204 g C + 18.2 g H + 57.0 g F + 14.0 g N + 16.0 g O
= 309 g/mole
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Molar Mass Factors
Molar mass conversion factors
• are fractions (ratios) written from the molar mass.
• relate grams and moles of an element or compound.
• for methane, CH4, used in gas stoves and gas heaters
is
1 mole of CH4 = 16.0 g (molar mass equality)
Conversion factors:
16.0 g CH4
and
1 mole CH4
1 mole CH4
16.0 g CH4
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Learning Check
Acetic acid, C2H4O2, gives the sour taste to vinegar.
Write two molar mass conversion factors for acetic
acid.
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Solution
Calculate molar mass for acetic acid C2H4O2:
24.0 g C + 4.04 g H + 32.0 g O = 60.0 g/mole C2H4O2
1 mole of acetic acid
Molar mass factors:
1 mole acetic acid
60.0 g acetic acid
=
60.0 g acetic acid
and
60.0 g acetic acid
1 mole acetic acid
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Calculations Using Molar Mass
Molar mass factors are used to convert between the
grams of a substance and the number of moles.
Grams
Molar mass factor
Moles
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Moles to Grams
Aluminum is often used to build lightweight bicycle
frames. How many grams of Al are in 3.00 mole of Al?
Molar mass equality: 1 mole of Al = 27.0 g of Al
Setup with molar mass as a factor:
3.00 mole Al
x
27.0 g Al
1 mole Al
= 81.0 g of Al
molar mass factor for Al
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Learning Check
Allyl sulfide, C6H10S, is a
compound that has the odor
of garlic. How many moles
of C6H10S are in 225 g?
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Solution
Calculate the molar mass of C6H10S.
(6 x 12.0) + (10 x 1.01) + (1 x 32.1) = 114.2 g/mole
Set up the calculation using a mole factor.
225 g C6H10S x 1 mole C6H10S
114.2 g C6H10S
molar mass factor (inverted)
= 1.97 moles of C6H10S
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Grams, Moles, and Particles
A molar mass factor and Avogadro’s number convert…
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Learning Check
How many H2O molecules are in 24.0 g of H2O?
1) 4.52 x 1023 H2O molecules
2) 1.44 x 1025 H2O molecules
3) 8.03 x 1023 H2O molecules
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Solution
How many H2O molecules are in 24.0 g of 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
1 mole H2O
= 8.03 x 1023 H2O molecules
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Learning Check
If the odor of C6H10S can be detected from 2 x 10-13 g
in 1 liter of air, how many molecules of C6H10S are
present?
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Solution
If the odor of C6H10S can be detected from 2 x 10-13 g
in 1 liter of air, how many molecules of C6H10S are
present?
2 x 10-13 g x
1 mole
114.2 g
x 6.02 x 1023 molecules
1 mole
= 1 x 109 molecules of C6H10S are present
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