1

Chapter 5 Chemical Reactions and Quantities

5.5The Mole

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

2

Collection Terms

A collection term statesa specific number of items.

• 1 dozen donuts

= 12 donuts• 1 ream of paper

= 500 sheets• 1 case = 24 cans

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

3

A mole is a collection that contains

• the same number of particles as there are carbon atoms in 12.0 g of carbon.

• 6.02 x 1023 atoms of an element (Avogadro’s number).

1 mole element Number of Atoms1 mole C = 6.02 x 1023 C atoms1 mole Na = 6.02 x 1023 Na atoms1 mole Au = 6.02 x 1023 Au atoms

A Mole of Atoms

4

A mole • of a covalent compound has Avogadro’s number of

molecules.1 mole CO2 = 6.02 x 1023 CO2 molecules

1 mole H2O = 6.02 x 1023 H2O molecules

• of an ionic compound contains Avogadro’s number of formula units.

1 mole NaCl = 6.02 x 1023 NaCl formula units1 mole K2SO4 = 6.02 x 1023 K2SO4 formula

units

A Mole of a Compound

5

Samples of One Mole Quantities

1 mole C= 6.02 x 1023 C atoms

1 mole Al = 6.02 x 1023 Al atoms

1 mole S = 6.02 x 1023 S atoms

1 mole H2O = 6.02 x 1023 H2O molecules

1 mole CCl4 = 6.02 x 1023 CCl4 molecules

6

Avogadro’s number 6.02 x 1023 can be written as anequality and two conversion factors.

Equality:1 mole = 6.02 x 1023 particles

Conversion Factors:6.02 x 1023 particles and 1 mole 1 mole 6.02 x 1023

particles

Avogadro’s Number

7

Using Avogadro’s Number

Avogadro’s number is used to convertmoles of a substance to particles.

How many Cu atoms are in 0.50 mole Cu?

0.50 mole Cu x 6.02 x 1023 Cu atoms 1 mole Cu

= 3.0 x 1023 Cu atoms

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

8

Using Avogadro’s Number

Avogadro’s number is used to convertparticles of a substance to moles.

How many moles of CO2 are in 2.50 x 1024 molecules CO2?

2.50 x 1024 molecules CO2 x 1 mole CO2

6.02 x 1023 molecules CO2

= 4.15 mole CO2

9

1. The number of atoms in 2.0 mole Al is A. 2.0 Al atoms.

B. 3.0 x 1023 Al atoms. C. 1.2 x 1024 Al atoms.

2. The number of moles of S in 1.8 x 1024 atoms S is A. 1.0 mole S atoms. B. 3.0 mole S atoms. C. 1.1 x 1048 mole S atoms.

Learning Check

10

Solution

A. The number of atoms in 2.0 mole Al is 2.0 mole Al x 6.02x1023 Al atoms = 1.2 x 1024Al atoms 1 mole Al Avogadro’s Number

B. The number of moles of S in 1.8 x 1024 atoms S is1.8 x 1024 atoms S x 1 mole S

6.02 x 1023 S atoms Avogadro’s

Number= 3.0 moles of S atoms

11

Subscripts and Moles

The subscripts in a formula show• the relationship of atoms in the formula.• the moles of each element in 1 mole of compound.

GlucoseC6H12O6

In 1 molecule: 6 atoms C 12 atoms H 6 atoms OIn 1 mole: 6 mole C 12 mole H 6 mole O

12

Subscripts State Atoms and Moles

9 mole C 8 mole H 4 mole O

13

Factors from Subscripts

The subscripts are used to write conversion factors for

moles of each element in 1 mole compound. For aspirin

C9H8O4, the following factors can be written:

9 mole C 8 mole H 4 mole O 1 mole C9H8O4 1 mole C9H8O4 1 mole C9H8O4and 1 mole C9H8O4 1 mole C9H8O4 1 mole C9H8O4

9 mole C 8 mole H 4 mole O

14

Learning Check

A. How many mole O are in 0.150 mole aspirin C9H8O4?

B. How many O atoms are in 0.150 mole aspirin C9H8O4?

15

Solution

A. How many mole O are in 0.150 mole aspirin C9H8O4?0.150 mole C9H8O4 x 4 mole O = 0.600 mole O 1 mole C9H8O4

subscript factor

B. How many O atoms are in 0.150 mole aspirin C9H8O4?0.150 mole C9H8O4 x 4 mole O x 6.02 x 1023 O atoms

1 mole C9H8O4 1 mole O subscript Avogadro’s

factor Number= 3.61 x 1023 O atoms