The Concept of Molar Mass in Chemistry
The Mole
(Chapter 10)
Dr. Walker
The Mole in Chemistry
•
Not this!!
•
Not this!!!
The Mole
•
The mole is a counting unit
•
1 pair = 2
•
1 dozen = 12
•
1 mole = 6.022 x 10
23
atoms
–
This number is known as Avogadro’s number after
Italian chemist Amedeo Avogadro
The mole
•
One mole can be equal to three different
things
–
6.022 x 10
23
atoms
–
The atomic mass in grams of an atom or
compound
–
22.4 L (volume) of any gas at 25
o
C and 1 atm
pressure (known as STP)
Molar Mass
•
The
atomic mass
of any element is the weighted
average of all isotopes of an element
•
This is also the
molar mass
of the element
•
Examples
–
H = 1.01 g/mole
–
O = 16.00 g/mole
–
C = 12.01 g/mole
–
P = 30.97 g/mole
–
Cl = 35.45 g/mole
Molar Mass
•
The molar mass of a compound is the sum of
all atomic weights of all atoms in the
compound!
Molar Mass Examples
•
For compounds
–
H
2
O
–
H = 1.01 g/mole x 2
–
O = 16.00 g/mole x 1
•
=18.02 g/mole
Molar Mass Examples
•
Another example
•
CH
4
•
C = 12.01 g/mole = 12.01
•
H = 1.01 g/mole x 4 = 4.04
–
16.05 g/mole
Molar Mass Examples
•
Another Example
•
C
6
H
12
O
6
•
C = 12.01 g/mole x 6 = 72.06
•
H = 1.01 g/mole x 12 = 12.12
•
O = 16.00 g/mole x 6 = 96.00
–
180.18 g/mole
Molar Mass Examples
•
Another Example
•
Polyatomics
•
Pb(SO
4
)
2
•
Pb = 207.20
•
S = 32.07 g/mole x 2 = 64.14
•
O = 16.00 g/mole x 8 = 128.00
–
399.34 g/mole
–
Notice you must multiply the subscript inside the
parentheses by the number outside to get the right
number of atoms
Practice
•
Find the molar mass of the following
compounds:
–
LiOH
–
SO
2
–
Mg(NO
3
)
2
–
Al
2
(CO
3
)
3
–
C
9
H
8
O
4
–
C
8
H
10
N
4
O
2
–
C
22
H
30
N
6
O
4
S
Practice
•
Find the molar mass of the following compounds:
–
LiOH
•
6.94 + 16.00 + 1.01 =
23.95 g/mole
–
SO
2
•
32.06 + 2(16.00) =
64.06 g/mole
–
Mg(NO
3
)
2
•
24.31 + 2(14.01) + 6(16.00) =
148.33 g/mole
–
Al
2
(CO
3
)
3
•
2(26.98) + 3(12.01) + 9(16.00) =
233.99 g/mole
–
C
9
H
8
O
4
•
9(12.01) + 8(1.01) + 4(16.00) =
180.17 g/mole
–
C
8
H
10
N
4
O
2
•
8(12.01) + 10(1.01) + 4(14.01) + 2(16.00) =
194.22 g/mole
–
C
22
H
30
N
6
O
4
S
•
22(12.01) + 30(1.01) + 6(14.01) + 4(16.01) + 1(32.06) =
474.68 g/mole
Mass-Mole Conversions
•
Convert from mass to mole (or vice versa)
using the molar mass of a given element or
compound
•
Use dimensional analysis (t-square)
Mass-Mole Conversions
•
How many grams are in 2.5 moles NH
3
?
Mass-Mole Conversions
•
How many grams are in 2.5 moles NH
3
?
–
Find molar mass of NH
3
–
N = 14.01 g/mole x 1 = 14.01 g/mole
–
H = 1.01 g/mole x 3 = 3.03 g/mole
–
Molar mass = 17.04 g/mole
•
Multiply # of moles by molar mass
2.5 moles NH
3
17.04 g NH
3
1 mole NH
3
= 42.6 g NH
3
Mass-Mole Conversions
•
How many moles are contained in 100 g C
3
H
8
?
Mass-Mole Conversions
•
How many moles are contained in 100 g C
3
H
8
?
•
Find molar mass
•
C = 12.01 g/mole x 3 = 36.03 g/mole
•
H = 1.01 g/mole x 8 = 8.08 g/mole
•
44.11 g/mole
•
Divide # of grams given by molar mass
100 g C
3
H
8
1 mole C
3
H
8
44.11 g C
3
H
8
=
2.27 moles C
3
H
8
Mass-Mole Conversions
•
How many grams are present in 3.1 moles of
lithium carbonate?
Mass-Mole Conversions
•
How many grams are present in 3.1 moles of
lithium carbonate?
–
Formula for lithium carbonate = Li
2
CO
3
–
Li = 6.94 g/mole x 2 = 13.88 g/mole
–
C = 12.01 g/mole x 1 = 12.01 g/mole
–
O = 16.00 g/mole x 3 = 48.00 g/mole
–
73.89 g/mole
•
Multiply number of moles by molar mass
3.1 moles Li
2
CO
3
73.89 g Li
2
CO
3
1 mole Li
2
CO
3
= 229.06 g Li
2
CO
3
Mole-Particle conversions
•
Can go to or from moles from particles
–
Atoms in an element
–
Molecules in a covalent compound
–
You may see other terms like ions, formula units
–
1 mole = 6.022 x 10
23
particles is the conversion
factor that you use
Mole-Particle Conversions
•
How many atoms are in 1.5 moles of iron?
Mole-Particle Conversions
•
How many atoms are in 1.5 moles of iron?
1.5 moles iron
6.022 x 10
23
atoms iron
1 mole iron
= 9.03 x 10
23
atoms iron
Mole-Particle Conversions
•
How many moles are in 2.4 x 10
24
molecules
of water?
Mole-Particle Conversions
•
How many moles are in 2.4 x 10
24
molecules
of water?
2.4 x 10
24
molecules H
2
O
6.022 x 10
23
molecules H
2
O
1 mole H
2
O
= 3.98 moles H
2
O
Mole-Particle Conversions
•
It doesn’t matter what atom or compound is
being converted
•
For these conversions, you are always using 1
mole = 6.022 x 10
23
particles as your
conversion factor!!
Mole-Volume Conversions
•
At a specific set of conditions (known as
Standard Temperature and Pressure or STP), 1
mole of any gas = 22.4 L of volume
•
We can convert volume to moles and vice
versa
Example
•
How many liters of O
2
are contained in 5.0
moles?
Example
•
How many liters of O
2
are contained in 5.0
moles?
5.0 moles O
2
22.4 L O
2
1 mole O
2
= 112 L O
2
Example
•
How many moles are contained in a 3.7 L
sample of N
2
?
Example
•
How many moles are contained in a 3.7 L
sample of N
2
?
3.7 L N
2
1 mole N
2
22.4 L N
2
= 0.17 moles N
2
Multistep Conversions
•
We know that the mole is equal to multiple
numbers ( Avogadro’s # = 1 mole = molar mass
= 22.4 L)
•
Given this fact, we can convert from particles
to mass using the mole
•
Hint: If you look at the problem and the word
“mole” is absent, it is multistep!!
Multistep Example
•
How many grams are present in a 10 L sample
of H
2
?
Multistep Example
•
How many grams are present in a 10 L sample
of H
2
?
•
Convert from liters to moles
•
Convert from moles to grams
10 L H
2
1 mole H
2
22.4 L H
2
Multistep Example
•
How many grams are present in a 10 L sample
of H
2
?
•
Convert from liters to moles
•
Convert from moles to grams
10 L H
2
1 mole H
2
22.4 L H
2
=
0.90 g
H
2
2.02 g H
2
1 mole H
2
Example
•
How many molecules are contained in 4.5 g
H
2
O?
Example
•
How many molecules are contained in 4.5 g
H
2
O?
•
Step 1
–
Convert from grams to moles
4.5 g H
2
O
1 mole H
2
O
18 g H
2
O
Example
•
How many molecules are contained in 4.5 g
H
2
O?
•
Step 2
–
Convert from moles to particles
0.25 moles H
2
O
6.022 x 10
23
molecules
H
2
O
1 mole H
2
O
= 1.50 x 10
23
molecules H
2
O
4.5 g H
2
O
1 mole H
2
O
18 g H
2
O
Vocab/Skills
•
Vocabulary
–
Molar Mass
–
Avogadro’s number
•
Skills
–
Convert to and from moles using
mass/particles/volumes using dimensional
analysis
Explore the concept of molar mass in chemistry, including the definition of the mole, Avogadro's number, calculations for molar mass of elements and compounds, and examples of determining molar mass. Discover how to find the molar mass of various compounds through practical examples.
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Presentation Transcript
The Mole (Chapter 10) Dr. Walker
The Mole in Chemistry Not this!! Not this!!!
The Mole The mole is a counting unit 1 pair = 2 1 dozen = 12 1 mole = 6.022 x 1023atoms This number is known as Avogadro s number after Italian chemist Amedeo Avogadro
The mole One mole can be equal to three different things 6.022 x 1023atoms The atomic mass in grams of an atom or compound 22.4 L (volume) of any gas at 25 oC and 1 atm pressure (known as STP)
Molar Mass The atomic mass of any element is the weighted average of all isotopes of an element This is also the molar mass of the element Examples H = 1.01 g/mole O = 16.00 g/mole C = 12.01 g/mole P = 30.97 g/mole Cl = 35.45 g/mole
Molar Mass The molar mass of a compound is the sum of all atomic weights of all atoms in the compound!
Molar Mass Examples For compounds H2O H = 1.01 g/mole x 2 O = 16.00 g/mole x 1 =18.02 g/mole
Molar Mass Examples Another example CH4 C = 12.01 g/mole = 12.01 H = 1.01 g/mole x 4 = 4.04 16.05 g/mole
Molar Mass Examples Another Example C6H12O6 C = 12.01 g/mole x 6 = 72.06 H = 1.01 g/mole x 12 = 12.12 O = 16.00 g/mole x 6 = 96.00 180.18 g/mole
Molar Mass Examples Another Example Polyatomics Pb(SO4)2 Pb = 207.20 S = 32.07 g/mole x 2 = 64.14 O = 16.00 g/mole x 8 = 128.00 399.34 g/mole Notice you must multiply the subscript inside the parentheses by the number outside to get the right number of atoms
Practice Find the molar mass of the following compounds: LiOH SO2 Mg(NO3)2 Al2(CO3)3 C9H8O4 C8H10N4O2 C22H30N6O4S
Practice Find the molar mass of the following compounds: LiOH 6.94 + 16.00 + 1.01 = 23.95 g/mole SO2 32.06 + 2(16.00) = 64.06 g/mole Mg(NO3)2 24.31 + 2(14.01) + 6(16.00) = 148.33 g/mole Al2(CO3)3 2(26.98) + 3(12.01) + 9(16.00) = 233.99 g/mole C9H8O4 9(12.01) + 8(1.01) + 4(16.00) = 180.17 g/mole C8H10N4O2 8(12.01) + 10(1.01) + 4(14.01) + 2(16.00) = 194.22 g/mole C22H30N6O4S 22(12.01) + 30(1.01) + 6(14.01) + 4(16.01) + 1(32.06) = 474.68 g/mole
Mass-Mole Conversions Convert from mass to mole (or vice versa) using the molar mass of a given element or compound Use dimensional analysis (t-square)
Mass-Mole Conversions How many grams are in 2.5 moles NH3?
Mass-Mole Conversions How many grams are in 2.5 moles NH3? Find molar mass of NH3 N = 14.01 g/mole x 1 = 14.01 g/mole H = 1.01 g/mole x 3 = 3.03 g/mole Molar mass = 17.04 g/mole Multiply # of moles by molar mass 2.5 moles NH3 17.04 g NH3 = 42.6 g NH3 1 mole NH3
Mass-Mole Conversions How many moles are contained in 100 g C3H8?
Mass-Mole Conversions How many moles are contained in 100 g C3H8? Find molar mass C = 12.01 g/mole x 3 = 36.03 g/mole H = 1.01 g/mole x 8 = 8.08 g/mole 44.11 g/mole Divide # of grams given by molar mass 100 g C3H8 1 mole C3H8 = 2.27 moles C3H8 44.11 g C3H8
Mass-Mole Conversions How many grams are present in 3.1 moles of lithium carbonate?
Mass-Mole Conversions How many grams are present in 3.1 moles of lithium carbonate? Formula for lithium carbonate = Li2CO3 Li = 6.94 g/mole x 2 = 13.88 g/mole C = 12.01 g/mole x 1 = 12.01 g/mole O = 16.00 g/mole x 3 = 48.00 g/mole 73.89 g/mole Multiply number of moles by molar mass 3.1 moles Li2CO3 73.89 g Li2CO3 = 229.06 g Li2CO3 1 mole Li2CO3
Mole-Particle conversions Can go to or from moles from particles Atoms in an element Molecules in a covalent compound You may see other terms like ions, formula units 1 mole = 6.022 x 1023 particles is the conversion factor that you use
Mole-Particle Conversions How many atoms are in 1.5 moles of iron?
Mole-Particle Conversions How many atoms are in 1.5 moles of iron? 1.5 moles iron 6.022 x 1023 atoms iron = 9.03 x 1023 atoms iron 1 mole iron
Mole-Particle Conversions How many moles are in 2.4 x 1024 molecules of water?
Mole-Particle Conversions How many moles are in 2.4 x 1024 molecules of water? 2.4 x 1024 molecules H2O 1 mole H2O = 3.98 moles H2O 6.022 x 1023 molecules H2O
Mole-Particle Conversions It doesn t matter what atom or compound is being converted For these conversions, you are always using 1 mole = 6.022 x 1023 particles as your conversion factor!!
Mole-Volume Conversions At a specific set of conditions (known as Standard Temperature and Pressure or STP), 1 mole of any gas = 22.4 L of volume We can convert volume to moles and vice versa
Example How many liters of O2 are contained in 5.0 moles?
Example How many liters of O2 are contained in 5.0 moles? 5.0 moles O2 22.4 L O2 = 112 L O2 1 mole O2
Example How many moles are contained in a 3.7 L sample of N2?
Example How many moles are contained in a 3.7 L sample of N2? 3.7 L N2 1 mole N2 = 0.17 moles N2 22.4 L N2
Multistep Conversions We know that the mole is equal to multiple numbers ( Avogadro s # = 1 mole = molar mass = 22.4 L) Given this fact, we can convert from particles to mass using the mole Hint: If you look at the problem and the word mole is absent, it is multistep!!
Multistep Example How many grams are present in a 10 L sample of H2?
Multistep Example How many grams are present in a 10 L sample of H2? Convert from liters to moles 1 mole H2 10 L H2 22.4 L H2 Convert from moles to grams
Multistep Example How many grams are present in a 10 L sample of H2? Convert from liters to moles Convert from moles to grams 1 mole H2 2.02 g H2 10 L H2 = 0.90 g H2 22.4 L H2 1 mole H2
Example How many molecules are contained in 4.5 g H2O?
Example How many molecules are contained in 4.5 g H2O? Step 1 Convert from grams to moles 4.5 g H2O 1 mole H2O 18 g H2O
Example How many molecules are contained in 4.5 g H2O? Step 2 Convert from moles to particles 0.25 moles H2O 6.022 x 1023 molecules H2O 1 mole H2O 4.5 g H2O = 1.50 x 1023 molecules H2O 1 mole H2O 18 g H2O
Vocab/Skills Vocabulary Molar Mass Avogadro s number Skills Convert to and from moles using mass/particles/volumes using dimensional analysis
