Tuesday, April 2nd: “A” Day
Wednesday, April 3rd: “B” Day
Agenda
 ACT practice
 Begin Chapter 7: “The Mole and
Chemical Composition”
 In-Class Assignments:
Practice pg. 228: #1-4
Practice pg. 229: #1-4
 Homework:
 Practice worksheet, pg. 21/22: MUST SHOW WORK!
 Concept Review: “Avo’s Number/Molar Conversions”
ACT Practice Worksheets
Take some time to complete ACT practice
worksheets.
When you’re done, turn them in and pick up
the notes for today.
Yes, these will be graded…
Start Section 7.1:
“Avogadro’s Number and Molar
Conversions”
Atoms, ions, and molecules are very small, so
even tiny samples have huge numbers of
particles.
Scientists use the mole to make counting such
large numbers easier.
Mole: the SI unit for amount; the number of
atoms in exactly 12 grams of carbon-12.
The Mole is a Counting Unit
The mole is used to count out a given number of
particles, whether they are atoms, molecules,
formula units, ions, or electrons.
The mole is just one kind of counting unit:
1 dozen = 12 objects
1 roll = 50 pennies
1 hour = 3,600 seconds
1 pair = 2 items
 1 mole = 6.022  1023 particles

Avogadro’s Number & the Mole
The number of particles in a mole is called
Avogadro’s Number.
Avogadro’s number is 6.022  1023; the number of
atoms or molecules in 1.000 mole
Lorenzo Romano Amedeo Carlo Avogadro
Born in Turin, Italy, on August 9th, 1776.
Conversion Factors are Equivalent to 1
The definition of one mole is:
6.022  1023 particles = 1 mol
From this definition, we get 2 conversion factors:
6.022 X 1023 particles = 1
1 mol
_____1 mol________ = 1
6.022 X 1023 particles
Use the Conversion Factor that Cancels
Out the Known Units
 Because a conversion factor is equal to 1, it
can multiply any quantity without changing the
value.
Only the units are changed.
When solving problems, the unit that you know
goes on the bottom of the fraction.
You Can use Conversion Factors to Change
from One Unit to Another
(Dimensional Analysis)
Example #1: How many eggs are there in 5 dozen?
1. Start with what you know: 5 dozen
2. Multiply by a conversion factor to change
dozen
number of eggs:
 5 dozen X 12 eggs =
1 dozen
60 eggs
You Can use Conversion Factors to Change
from One Unit to Another
(Dimensional Analysis)
Example #2: If you have 548 plain white socks,
how many pairs can you make?
1. Start with what you know: 548 socks
2. Multiply by a conversion factor to change
socks
pairs of socks:
 548 socks X 1 pair =
2 socks
274 pairs
Changing Moles
Particles
Changing Moles
Particles
Sample Problem A, pg 228
Find the number of molecules in 2.5 mol of sulfur
dioxide, SO2.
1. Start with what you know: 2.5 mol SO2
2. Multiply by a conversion factor to change
moles
molecules:
2.5 mol SO2 X 6.022 X 1023 molecules SO2 =
1 mole SO2
(2 sig figs)
1.5 X1024
molecules SO2
Changing Moles
Practice #1
Particles
How many particles are there in 2.45 X 10-6 mol of nickel,
Ni(II) selenide, NiSe?
1. Start with what you know: 2.45 X 10-6 mol NiSe
2. Multiply by conversion factor to change
moles
particles:
 2.45 X 10 -6 mol NiSe X 6.022 X 1023 particles NiSe =
1 mole NiSe
1.48 X 1018 particles
(3 sig figs)
NiSe
Changing Moles
Practice #2
Particles
How many atoms are there in 4.3 moles of tungsten, W?
1. Start with what you know: 4.3 moles W
2. Multiply by conversion factor to change
moles
atoms:
 4.3 mol W X 6.022 X 1023 atoms W =
1 mol W
2.6 X 1024 atoms W
(2 sig figs)
We can go the other way too and
change particles
moles
Changing Particles
Moles
Sample Problem B, pg. 229
A sample contains 3.01 X 1023 molecules of sulfur
dioxide, SO2. Determine the amount in moles.
1. Start with what you know: 3.01 X 1023 molecules SO2
2. Multiply by conversion factor to change
molecules
moles:
 3.01 X 1023 molecules SO2 X __1 mole SO2______
6.022 X 1023 molecules SO2
0.500 mole SO2 (3 sig figs)
Changing Particles
Practice #1
Moles
How many moles are equivalent to 6.93 X 1023
thallium atoms, Tl?
1. Start with what you know: 6.93 X 1023 Tl atoms
2. Multiply by conversion factor to change
atoms
moles:
 6.93 X 1023 Tl atoms X 1 mole Tl
=
6.022 X 1023 Tl atoms
(3 sig figs)
1.15 mole Tl
Changing Particles
Practice #2
Moles
How many moles are equivalent to 7.95 X 1024 copper
(II) chloride, CuCl2, formula units?
1. Start with what you know: 7.95 X 1024 CuCl2 formula
units
2. Multiply by conversion factor to change formula
units
moles:
 7.95 X 1024 form. unit CuCl2 X ____1 mole_CuCl2___
6.022 X 1023 form. unit CuCl2
13.2 mol CuCl2
(3 sig figs)
In-Class Assignments/Homework
Practice pg. 228: #1-4
Practice pg. 229: #1-4
Homework:
Practice Worksheets, pg. 21/22
Concept Review: Avogadro’s Number and Molar
Conversions” #1-5
You must SHOW WORK to get credit!