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Thursday, April 7th : “A” DayFriday, April 8th: “A” Day
AgendaFinish Section 7.1: “Avogadro’s Number & Molar
Conversions”In-Class:
Practice pg. 231: #1-4Practice pg. 232: #1-3Concept Review: “Avogadro’s Number &
Molar Conversions”: #6-10
Section 7.1 quiz next time…
Finish 7.1: “Avogadro’s Number and Molar Conversions”
6.022 X 1023 atoms 1 mole
Molar Mass Relates Moles to GramsMolar mass: the mass in grams of one mole of an
element or compound.
Molar mass is numerically equal to the atomic mass of elements (Fe, Al, etc.) and the formula mass of compounds (H2O, CH4, etc. ) and diatomic elements. (O2, F2, etc.)
The units for molar mass are grams mole
Molar Mass Example #1What is the molar mass of water, H2O?To determine the molar mass, look up the
atomic mass of each element present in the compound and add them up. This is the molar mass.
H = 1.01 g/mol H = 1.01 g/molO = 16.0 g/mol
Molar mass of water = 18.02 g H2O
1 mole
Molar Mass Example #2What is the molar mass of sulfuric acid, H2SO4?
H = 1.01 g/molH = 1.01 g/molS = 32.07 g/molO = 16.0 g/molO = 16.0 g/molO = 16.0 g/molO = 16.0 g/mol
Molar mass of sulfuric acid = 98.09 g H2SO4
1 mole
So, why do we need to know the molar mass…
Molar mass can be used as a conversion factor in problems converting between mass and amount!!!
Converting Number of Particles to MassTo convert from number of particles to mass, you
must use a two-step process: First, convert number of particles to amount
in moles using Avogadro’s number. Second, convert amount in moles to mass in
grams using the molar mass.Two different conversion factors must be used!
Converting Between Mass, Amount, and Number of Particles
Sample Problem C, pg. 231Converting Number of Particles to Mass
Find the mass in grams of 2.44 X 1024 atoms of carbon, whose molar mass is 12.01 g/mol.
Known: 2.44 X 1024 atoms of carbonUnknown: Mass in grams of carbon
Two conversion factors:1 mole C AND 12.01 g C
6.022 X 1023 atoms C 1 mole C
Sample Problem C, continuedConverting Number of Particles to Mass
Step 1: Convert # of particles amount in moles:2.44 X 1024 C atoms X 1 mole C
6.022 X 1023 atoms C= 4.05 moles C
Step 2: Convert amount in moles mass (in grams)4.05 moles C X 12.01 g C
1 mole C
= 48.6 g C
Additional PracticeFind the mass in grams of 6.12 X 1014 formula units of
rhenium dioxide, ReO2, 218.21 g/mol.
Known: 6.12 X 1014 formula units ReO2
Unknown: Mass in grams of ReO2
Two conversion Factors:
1 mole ReO2 AND 218.21 g ReO2
6.022 X 1023 form unit ReO2 1 mole ReO2
Additional Practice
Step 1: Convert # of particles amount in moles:6.12 X 1014 form. unit X _1 mol_ReO2__
6.022 X 1023 form. unit ReO2
= 1.02 X 10 -9 mole ReO2
Step 2: Convert amount in moles mass (in grams)1.02 X 10 -9 mole ReO2 X 218.21 g ReO2
1 mole ReO2
= 2.23 X 10 -7 g ReO2
Converting Mass to Number of ParticlesConverting from mass to number of particles is
simply the opposite of the previous problems.To convert from mass to number of particles, you
must use a two-step process:1. First, convert mass in grams to amount in
moles using molar mass.2. Second, convert amount in moles to number
of particles using Avogadro’s number. Two different conversion factors must be used!
Sample Problem D, pg. 232Converting Mass to Number of Particles
Find the number of molecules present in 47.5 g of glycerol, C3H8O3. The molar mass of glycerol is 92.11 g/mol.
Known: 47.5 g glycerol, C3H8O3
Unknown: # of molecules presentTwo conversion factors:
1 mole C3H8O3 AND 6.022 X 1023 molecules C3H8O3
92.11 g C3H8O3 1 mole C3H8O3
Sample Problem D, cont.Converting Mass to Number of Particles
Step 1: Convert mass (in grams) amount in moles: 47.5 g C3H8O3 X 1 mole C3H8O3 = 0.516 mol C3H8O3
92.11 g C3H8O3
Step 2: Convert amount in moles # of molecules: 0.516 mol C3H8O3 X 6.022 X 1023 molecules C3H8O3
1 mole C3H8O3
= 3.11 X 1023 molecules C3H8O3
Additional Practice
Determine the number of atoms present in 54.3 grams of cobalt, Co.
Known: 54.3 g of cobalt, Co.Unknown: # of atoms
Two conversion Factors:1 mole Co AND 6.022 X 1023 atoms
Co58.93 g Co 1 mole Co
Additional PracticeStep 1: Convert mass (in grams) amount in moles:54.3 g Co X 1 mol Co = 0.921 mol Co
58.93 g Co
Step 2: Convert amount in moles # of atoms:0.921 moles Co X 6.022 X 1023 atoms Co
1 mole Co
= 5.55 X 1023 atoms Co
In-Class Assignments/HomeworkYou Must SHOW WORK!
Practice pg. 231: #1-4Practice pg. 232: #1-3Concept Review: “Avogadro’s Number & Molar
Conversions”: #6-10
Section 7.1 quiz next time…