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•Chapter 7 Chemical Quantities

7.3

Molar Mass

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Molar Mass

The molar mass • Is the mass of one mole

of an element or compound

• Is the atomic mass expressed in grams

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

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Molar Mass from Periodic Table

Molar mass • Is the atomic

mass expressed in grams

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Give the molar mass for:

A. 1 mol K atoms = ________

B. 1 mol Sn atoms = ________

Learning Check

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Give the molar mass for:

A. 1 mol K atoms = 39.10 g

B. 1 mol Sn atoms = 118.7 g

Solution

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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 Number of Moles

Atomic Mass Total Mass

Ca 1 40.08 g/mol 40.08 g

Cl 2 35.45 g/mol 70.90 g

CaCl2 110.98 g

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Molar Mass of K3PO4

Calculate the molar mass of K3PO4.

Element Number of Moles

Atomic Mass Total Mass in K3PO4

K 3 39.10 g/mol 117.3 g

P 1 30.97 g/mol 30.97 g

O 4 16.00 g/mol 64.00 g

K3PO4 212.3 g

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Some One-Mole Quantities

32.07 g 55.85 g 58.44 g 294.20 g 342.30 g

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What is the molar mass of each of the following?

A. K2O

B. Al(OH)3

Learning Check

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A. K2O 94.20 g/mol

2 mol K (39.10 g/mol) + 1 mol O (16.00 g/mol)

78.20 g + 16.00 g = 94.20 g

B. Al(OH)3 78.00 g/mol

1 mol Al (26.98 g/mol) + 3 mol O (16.00 g/mol) + 3 mol H (1.008 g/mol) 26.98 g + 48.00 g + 3.024 g = 78.00 g

Solution

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Prozac, C17H18F3NO, is an antidepressant that inhibits the uptake of serotonin by the brain. What is the molar mass of Prozac?1) 40.06 g/mol2) 262.0 g/mol 3) 309.3 g/mol

Learning Check

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Prozac, C17H18F3NO, is an antidepressant that inhibits the uptake of serotonin by the brain. What is the molar mass of Prozac?

3) 309.3 g/mol

17C (12.01) + 18H (1.008) + 3F (19.00)

+ 1N (14.01) + 1 O (16.00) =

204.2 +18.14 + 57.00 + 14.01 + 16.00 = 309.3 g/mol

Solution