Chapter 7 Chemical Quantities

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

Atomic Mass

Atomic mass is the• Mass of a single

atom in atomic mass units (amu)

• Mass of an atom compared to a 12C atom

• Number below the symbol of an element

Periodic Table and Atomic Mass

Ag has atomic mass = 107.9 amu

C has atomic mass = 12.01 amu

S has atomic mass = 32.07 amu

Atomic Mass Factors

The atomic mass, • Can be written as an equality

Example: 1 P atom = 30.97 amu

• Can be written as two conversion factors

Example:

1 P atom and 30.97 amu

30.97 amu 1 P atom

Uses of Atomic Mass Factors

The atomic mass is used to convert:

• A specific number of atoms to mass (amu)

• An amount in amu to number of atoms

Learning Check

What is the mass in amu of 75

silver atoms?

1) 107.9 amu

2) 8093 amu

3) 1.439 amuCopyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

Learning Check

How many gold atoms have a

mass of 1.85 x 105 amu?

1) 939 Au atoms

2) 3.64 x 107 Au atoms

3) 106 Au atomsCopyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

Formula Mass

The formula mass is• The mass in amu

of a compound• The sum of the

atomic masses of the elements in a formula

Calculating Formula Mass

To calculate formula mass of Na2SO4,

• Multiply the atomic mass of each element by its subscript

• Total the masses

2 Na x 22.99 amu = 45.98 amu Formula mass

1 Na2SO4

1 S x 32.07 amu = 32.07 amu 142.05 amu1 S

4 O x 16.00 amu = 64.00 amu1 O

Learning Check

Using the periodic table, calculate the formula mass of aluminum sulfide Al2S3.

Collection Terms

A collection term states

a 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

A mole (mol) is a collection that contains:

• The same number of particles as there are carbon atoms in 12.01 g of carbon

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

1 Mol element Number of Atoms

1 mol C = 6.022 x 1023 C atoms

1 mol Na = 6.022 x 1023 Na atoms

1 mol Au = 6.022 x 1023 Au atoms

A Mole of Atoms

A mole

• Of a covalent compound has Avogadro’s number of molecules

1 mol CO2 = 6.022 x 1023 CO2 molecules

1 mol H2O = 6.022 x 1023 H2O molecules

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

1 mol NaCl = 6.022 x 1023 NaCl formula units

1 mol K2SO4 = 6.022 x 1023 K2SO4 formula units

A Mole of a Compound

Samples of One-Mole Quantities

Avogadro’s number 6.022 x 1023 can be written as an

equality and two conversion factors.

Equality:

1 mol = 6.022 x 1023 particles

Conversion Factors:

6.022 x 1023 particles and 1 mol 1 mol 6.022 x 1023

particles

Avogadro’s Number

Using Avogadro’s Number

Avogadro’s number is used to convert Moles of a substance to Particles.

How many Cu atoms are in 0.50 mol Cu?

0.50 mol Cu x 6.022 x 1023 Cu atoms 1 mol Cu

= 3.0 x 1023 Cu atoms

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

Using Avogadro’s Number

Avogadro’s number is used to convert Particles of a substance to Moles.

How many moles of CO2 are in

2.50 x 1024 CO2 molecules?

2.50 x 1024 CO2 x 1 mol CO2

6.022 x 1023 CO2

= 4.15 mol CO2

1. The number of atoms in 2.0 mol 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 mol S atoms

B. 3.0 mol S atoms

C. 1.1 x 1048 mol S atoms

Learning Check

Subscripts and Moles

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

Glucose

C6H12O6

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

In 1 mol: 6 mol C 12 mol H 6 mol O

Subscripts State Atoms and Moles

The subscripts are used to write conversion factors formoles of each element in 1 mol compound. For aspirinC9H8O4, the following factors can be written:

9 mol C 8 mol H 4 mol O 1 mol C9H8O4 1 mol C9H8O4 1 mol C9H8O4

and

1 mol C9H8O4 1 mol C9H8O4 1 mol C9H8O4 9 mol C 8 mol H 4 mol O

Learning Check

How many O atoms are in 0.150 mol aspirin C9H8O4?

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

Molar Mass from Periodic Table

Molar mass • Is the atomic

mass expressed in grams

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

Some One-Mole Quantities

32.07 g 55.85 g 58.44 g 294.20 g 342.30 g

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

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

Acetic acid C2H4O2 gives the sour taste to vinegar. Write two molar mass conversion factors for acetic acid.

Learning Check

Molar mass factors are used to convert between the grams of a substance and the number of moles.

Calculations Using Molar Mass

Grams Molar mass factor Moles

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

Molar mass equality: 1 mol Al = 26.98 g Al

Setup with molar mass as a factor:

3.00 mol Al x 26.98 g Al = 80.9 g Al1 mol Al

molar mass factor for Al

Moles to Grams

Learning Check

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

Grams, Moles, and Particles

A molar mass factor and Avogadro’s number convert:• Grams to particles

molar mass Avogadro’s number

(g mol particles)

• Particles to grams

Avogadro’s number molar mass (particles mol g)

Learning Check

How many H2O molecules are in 24.0 g H2O?

1) 4.52 x 1023

2) 1.44 x 1025

3) 8.02 x 1023

Percent Composition

Percent composition

• Is the percent by mass of each element in a formula

Example: Calculate the percent composition of CO2.

CO2 = 1 C(12.01g) + 2 O(16.00 g) = 44.01 g/mol)

12.01 g C x 100 = 27.29 % C 44.01 g CO2

32.00 g O x 100 = 72.71 % O 44.01 g CO2 100.00 %

Learning Check

The chemical isoamyl acetate C7H14O2 gives the odor of pears. What is the percent carbon in isoamyl acetate?

1) 7.102% C

2) 35.51% C

3) 64.58% C

The molecular formula • Is the true or actual number of the atoms in a molecule

The empirical formula

• Is the simplest whole number ratio of the atoms

• Is calculated by dividing the subscripts in the molecular formula by a whole number to give the lowest ratio

C5H10O5 5 = C1H2O1 = CH2Omolecular empirical formula

formula

Types of Formulas

Some Molecular and Empirical Formulas

• The molecular formula is the same or a multiple of the empirical.

A. What is the empirical formula for C4H8?

1) C2H4 2) CH2 3) CH

B. What is the empirical formula for C8H14?

1) C4H7 2) C6H12 3) C8H14

C. Which is a possible molecular formula for CH2O?

1) C4H4O4 2) C2H4O2 3) C3H6O3

Learning Check

A compound contains 7.31 g Ni and 20.0 g Br.

• Calculate its empirical (simplest) formula.

• If the compound has a molar mass of 437 g/mol, calculate the molecular formula.

Learning Check

Aspirin is 60.0% C, 4.5% H and 35.5% O. Calculate its empirical (simplest) formula.

Learning Check