Chapter 9Video Intro

Crash Course: Stoichiometry

https://youtu.be/UL1jmJaUkaQ?list=PL8dPuuaLjXtPHzzY

uWy6fYEaX9mQQ8oGr

Chapter 9

Relating Mass to Numbers of Atoms,

• Gram/Mole Conversions

4.00 g He2.00 mol He = 8.00 g He

1 mol He

• Chemists use molar mass as a conversion factor in

chemical calculations.

• For example, the molar mass of helium is 4.00 g

He/mol He.

• To find how many grams of helium there are in two

moles of helium, multiply by the molar mass.

Chapter 9

Chapter 9

Mole Ratio

• A mole ratio is a conversion factor that relates the

amounts in moles of any two substances involved in a

chemical reaction

Example: 2Al2O3(l) → 4Al(s) + 3O2(g)

Mole Ratios: 2 mol Al2O3 2 mol Al2O3 4 mol Al

4 mol Al 3 mol O2 3 mol O2

Section 1 Introduction to

Stoichiometry

, ,

Chapter 9 Section 3 Counting Atoms

Relating Mass to Numbers of Atoms

• The Mole

• The mole is the SI unit for amount of substance.

• A mole (abbreviated mol) is the amount of a

substance that contains as many particles as there

are atoms in exactly 12 g of carbon-12.

Avogadro’s Number

• Avogadro’s number—6.022 × 1023—is the number

of particles in exactly one mole of a pure substance.

Chapter 9

Chapter 9Molar Mass

• What is the mass of 1 mole of Al?

• What is the mass of 1 mole of O2?

Chapter 9Molar Mass

• What is the mass of 3 mole of Al2O3?

Chapter 9

Solving Mole Problems

Section 3 Counting AtomsChapter 3

Chapter 9

Determining the Mass from the Amount in

Moles

Section 3 Counting AtomsChapter 3

Chapter 9 Section 3 Counting Atoms

Relating Mass to Numbers of Atoms,

continued

•Sample Problem B

•What is the mass in grams of 3.50 mol of the

element copper, Cu?

Chapter 3

Chapter 9 Section 3 Counting Atoms

Relating Mass to Numbers of Atoms,

continued

• Sample Problem B Solution

• Given: 3.50 mol Cu

• Unknown: mass of Cu in grams

• Solution: the mass of an element in grams can be

calculated by multiplying the amount of the element

in moles by the element’s molar mass.

grams Cumoles Cu × = grams Cu

moles Cu

Chapter 3

Chapter 9 Section 3 Counting Atoms

Relating Mass to Numbers of Atoms,

continued

•Sample Problem B Solution, continued

•The molar mass of copper from the periodic table is

rounded to 63.55 g/mol.

63.55 g Cu3.50 mol Cu × =

1 222

mol Cu g Cu

Chapter 3

Chapter 9 Section 3 Counting Atoms

Relating Mass to Numbers of Atoms,

continued

•Sample Problem C

•A chemist produced 11.9 g of aluminum, Al. How

many moles of aluminum were produced?

Chapter 3

Chapter 9 Section 3 Counting Atoms

Relating Mass to Numbers of Atoms,

continued

• Sample Problem C Solution

• Given: 11.9 g Al

• Unknown: amount of Al in moles

• Solution: moles Al

grams Al = moles Algrams Al

1 mol Al11.9 g Al =

26.0.441

98 g Al mol Al

Chapter 3

The molar mass of aluminum from the periodic

table is rounded to 26.98 g/mol.

Chapter 9 Section 3 Counting Atoms

Relating Mass to Numbers of Atoms,

continued

•Sample Problem D

•How many moles of silver, Ag, are in 3.01 1023

atoms of silver?

Chapter 3

Chapter 9 Section 3 Counting Atoms

Relating Mass to Numbers of Atoms,

continued

• Sample Problem D Solution

• Given: 3.01 × 1023 atoms of Ag

• Unknown: amount of Ag in moles

• Solution:

moles Ag

Ag atoms = moles AgAvogadro's number of Ag atoms

23

23

1 mol Ag3.01 10 Ag atoms

6.022 10 Ag at

0.500

=

m

oms

ol Ag

Chapter 3

Chapter 9 Section 3 Counting Atoms

Relating Mass to Numbers of Atoms,

continued

•Sample Problem E

•What is the mass in grams of 1.20 108 atoms of

copper, Cu?

Chapter 3

Chapter 9 Section 3 Counting Atoms

• Sample Problem E Solution

• Given: 1.20 × 108 atoms of Cu

• Unknown: mass of Cu in grams

• Solution:

moles Cu grams Cu

Cu atoms = grams CuAvogadro's number of Cu atoms moles Cu

14

8

23

1 mol Cu 63.55 g Cu1.20 10 Cu atoms =

6.022 10 Cu atoms 1 mol Cu

1. 27 10 Cu g

–

Relating Mass to Numbers of Atoms, continued

Chapter 3

The molar mass of copper from the periodic table is

rounded to 63.55 g/mol.

Chapter 9Homework

• Complete the following problems in the “Modern

Chemistry” textbook. SHOW YOUR WORK.

• P. 85 (top of page) PRACTICE #1-2

• P. 85 (bottom of page) PRACTICE #1-2

• P. 86 PRACTICE #1

• P. 87 PRACTICE #1

Chapter 9Homework

• Complete the following problems in the “Modern

Chemistry” textbook. SHOW YOUR WORK.

• P. 90 #23 a-c, #24 a-c and 28 f-h.