Monday, April 8th: “A” Day
Tuesday, April 9th: “B” Day
Agenda
Homework Questions/Collect
Finish section 7.1…finally!
In-class:
Practice pg. 231: #1-4
Practice pg. 232: #1-3
Homework:
Practice worksheet pg 24/25
Must SHOW WORK for credit!
Homework
“Grams/Moles Calculations”
worksheet
Questions/Problems?
Hand in
Changing Particles
Mass
Now that you know how to change particles
into moles and moles into mass (in grams), we
can put these two steps together to convert
from
Particles
Mass!
Changing Particles
Mass
You need 2 steps to change number of particles to
mass, in grams:
1. Change particles to moles using Avogadro’s
number
2. Change moles to mass using the molar mass
Two different conversion factors must be used!
Converting Between Mass, Amount,
and Number of Particles
Particles
Mass
Sample Problem C, pg. 231
Find the mass in grams of 2.44 X 1024 atoms of
carbon, whose molar mass is 12.01 g/mol.
1. Start with what you know: 2.44 X 1024 atoms C
2. Use Avogadro’s number as a conversion factor to
change atoms C
moles C:
 2.44 X 1024 atoms C X 1 mol C
6.022 X 1023 atoms C
= 4.05 mol C
Particles
Mass
Sample Problem C, pg. 231, cont.
3. Now, use molar mass of carbon to change
moles C
mass (in grams) of C:
4.05 moles C X 12.01 g C
1 mole C
48.6 g C
(3 sig figs)
Particles
Mass
Practice #1
Find the mass in grams of 6.12 X 1014 formula units
of rhenium dioxide, ReO2, 218.21 g/mol.
1. Start with what you know: 6.12 X 1014 form. units
ReO2
2. Use Avogadro’s number as a conversion factor to
change form. units ReO2
moles ReO2:
 6.12 X 1014 form. units X 1 mol ReO2
6.022 X 1023 form. units
= 1.02 X 10-9 mole ReO2
Particles
Mass
Practice #1, cont.
3. Now, use molar mass of ReO2 to change
moles ReO2
mass (in grams) of ReO2:
1.02 X 10-9 mole ReO2 X 218.21 g ReO2
1 mole ReO2
2.23 X 10-7 g ReO2
(3 sig figs)
Changing Mass
Particles
Converting from mass to number of particles is
simply the opposite of what you’ve just done.
You need 2 steps to change number of particles to
mass:
1. Change mass to moles using molar mass
2. Second, change moles to particles using
Avogadro’s number
 Two different conversion factors must be used!
Mass
Particles
Sample Problem D, pg. 232
Find the number of molecules present in 47.5 g of
glycerol, C3H8O3. The molar mass of glycerol is
92.11 g/mol.
1. Start with what you know: 47.5 g C3H8O3
2. Use molar mass of C3H8O3 to change
mass C3H8O3
moles C3H8O3:
47.5 g C3H8O3 X 1 mol C3H8O3 =
.516 mol C3H8O3
92.11 g C3H8O3
Mass
Particles
Sample Problem D, cont.
3. Now, use Avogadro’s number to change
moles
molecules:
 0.516 mol C3H8O3 X 6.022 X 1023 molecules C3H8O3
1 mole C3H8O3
3.11 X 1023 molecules C3H8O3
(3 sig figs)
Mass
Particles
Additional Practice
Determine the number of atoms present in
54.3 grams of cobalt, Co.
1. Start with what you know: 54.3 g Co
2. Use molar mass of Co to change
mass Co
mole Co:
 54.3 g Co X 1 mol Co =
58.93 g Co
.921 mole Co
Mass
Particles
Additional Practice, cont.
3. Now, use Avogadro’s number to change
moles Co
atoms Co:
0.921 moles Co X 6.022 X 1023 atoms Co
1 mole Co
5.55 X 1023 atoms Co
In-Class Assignments/Homework
You Must SHOW WORK!
Practice pg. 231: #1-4
Practice pg. 232: #1-3
Practice worksheet, pg. 24/25
Concept Review:
“Avogadro’s Number & Molar Conversions”