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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.