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Chapter 7 Chemical Quantities

7.3 Calculations Using Molar Mass

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Table salt is NaCl.

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Molar mass conversion factors • are written from molar mass• relate grams and moles of an element or

compound

Example: Write molar mass factors for methane CH4

used in gas cook tops and gas heaters.

Molar mass:

1 mol CH4 = 16.04 g

Conversion factors:

16.04 g CH4 and 1 mol CH4

1 mol CH4 16.04 g CH4

Molar Mass Factors

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Acetic acid HC2H3O2 gives the sour taste to vinegar. Write an equality and two molar mass conversion factors for acetic acid.

Learning Check

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Acetic acid HC2H3O2 gives the sour taste to vinegar.Write an equality and two molar mass conversion

factors for acetic acid.

Equality:

1 mol of acetic acid = 60.05 g of acetic acid

Molar mass conversion factors:

1 mol acetic acid and 60.05 g acetic acid 60.05 g acetic acid 1 mol acetic acid

Solution

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Guide to Calculation Using Molar Mass

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Aluminum is used to build lightweight bicycleframes. How many grams of Al are in 3.00 mol of Al?

Moles to Grams

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STEP 1 Given 3.00 mol of Al Need grams of Al

STEP 2 Plan moles of Al grams of Al

STEP 3 Equalities/Conversion Factors

1 mol of Al = 26.98 g of Al 1 mol Al and 26.98 g Al

26.98 g Al 1 mol Al

Solution

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STEP 4 Set Up ProblemSet up with molar mass as a factor:

3.00 mol Al x 26.98 g Al = 80.9 g of Al 1 mol Al molar mass factor for Al

Solution (continued)

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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

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STEP 1 Given 225 g of C14H18N2O5 Need molesSTEP 2 Plan g of aspartame moles of aspartameSTEP 3 Equalities/Conversion Factors

1 mol aspartame = 294.3 g 1 mol aspartame and 294.3 g aspartame 294.3 g aspartame 1 mol aspartameSTEP 4 Set Up Problem

225 g aspartame x 1 mol aspartame 294.3 g aspartame

mole factor (inverted)

= 0.765 mol of aspartame

Solution

Basic Chemistry Copyright © 2011 Pearson Education, Inc.

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

Basic Chemistry Copyright © 2011 Pearson Education, Inc.

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STEP 1 Given 225 g of C6H10S Need moles of C6H10S

STEP 2 Plan g of C6H10S moles of C6H10S

STEP 3 Equalities/Conversion Factors

1 mol of C6H10S = 114.21 g of C6H10S

1 mol C6H10S and 114.21 g C6H10S

114.21 g C6H10S 1 mol C6H10S

STEP 3 Set Up Problem 225 g C6H10S x 1 mol C6H10S

114.21 g C6H10S

= 1.97 mol C6H10S

Solution

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Guide to Converting Grams to Particles

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Learning Check

How many molecules of H2O are in 24.0 g of H2O?

1) 4.52 x 1023

2) 1.44 x 1025

3) 8.02 x 1023

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Solution

STEP 1 Given 24.0 g of H2O

Need molecules of H2O

STEP 2 Plan

g of H2O moles of H2O molecules of H2O

STEP 3 Equalities/Conversion Factors

1 mol of H2O = 18.02 g of H2O

1 mol H2O and 18.02 g H2O

18.02 g H2O 1 mol H2O

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Solution (continued)

STEP 3 Equalities/Conversion Factors (continued)

1 mol of H2O = 6.022 molecules of H2O

1 mol H2O and 6.022 x 1023 H2O molecules

6.022 H2O molecules 1 mol H2O

STEP 4 Set Up Problem

24.0 g H2O x 1 mol H2O

18.02 g H2O

x 6.022 x 1023 H2O molecules

1 mol H2O

= 8.02 x 1023 H2O molecules (3)

Basic Chemistry Copyright © 2011 Pearson Education, Inc.