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The Mole
Chapter 10
1
It’s Mole Day 1023
• What are mammoles?
- Four-legged animoles!
• What did one mole say to the other?
- We make great chemistry together.
• What kind of test do student moles like best?
- Mole-tiple choice.
• What did the generous mole say when his friends
crashed his party?
- The mole the merrier!
2
Let’s Discuss
• Which do you think is more toxic - one
mole of arsenic, As or 10 grams of
arsenic? Explain your reasoning.
3
Relationship between
mass and number
• Discuss how measuring mass can be
used to calculate numbers of atoms and
molecules.
4
Calculations from Lab
Calculation Data Table #2
Mass of
beans (g)
Average
mass (g)
Relative
mass
No. of
beans in
relative
mass
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Molar Mass Intro
• If you know the average mass of an
object such as beans or lentils, you can
determine the number of objects in a
large collection by weighing.
• Long ago chemists agreed to assign a
value of 12 grams to a mole of carbon
atoms with a mass number of 12.
6
Molar Mass
• All other elements are measured in
relationship to this standard.
• The atomic masses listed on the
periodic table provide us with weights
relative to one another.
• These proportions hold true whether we
are comparing ten atoms or 6.02 x 1023
atoms.
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Definitions
• Molar Mass - how much one mole of a
substance weights.
• Molar Mass - the sum of all of the
atomic masses (in grams) in a chemical
formula.
• Example: 1 mole of Br = 79.9g
1 mole of K = 39.1g
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Calculating Molar Mass
• To calculate the molar mass of a
compound, it is necessary to add
together the atomic weights of all the
atoms that make up that compound.
• Example: N2
N amu = 14.0g
N2 = (2 x 14.0) = 28.0g
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Part 2 from Lab
S ubstance
He
# of particles
6.02 x 10 23
# of moles
1 mole
Measured mass
He
1.204 x 10 24
2 moles
8.0 g
1 mole
27.0 g
Al
Cu
6.02 x 10 23
1 mole
As
6.02 x 10 23
1 mole
M gF2
6.02 x 10 23
1 mole
NaCl
6.02 x 10 23
1 mole
H2O
6.02 x 10 23
1 mole
C6H12O6
6.02 x 10 23
1 mole
62.3 g
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Avagadro’s Number
• Avagadro figured out that
equal volumes of gas at
the same temperature and
pressure would have the
same number of particles.
1776 - 1856
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Avagadro’s Number
• The number of elementary entities in 1
mole of a substance = 6.0221367x1023
• You can have a mole of ions, mole of
molecules, mole of atoms, mole of
anything!
• Do we precisely know the mole?
602,213,670,000,000,000,000,000
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Mole Map
13
Moles & Mass
~ Molar Mass
• Which weighs more, 1 mole of Fe or 1
mole of H2O? Explain.
• Which has more atoms, 1 mole of Fe or
1 mole of H2O? Explain.
• Which has more moles, 10g Fe or 10g
H2O? Explain.
• Which is more toxic, 1 mole of As or 10g
As?
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Goal #1
• Which weighs more, 1 mole of Fe or 1
mole of H2O? Explain.
1. Look at periodic table. Amu of Fe = 55.845g
(
)
2. 1 mol Fe 55.845g
Fe
_________
1 mol Fe
= 55.845 g Fe
3. Look at periodic table. Amu of H2O = 18.0 g
Amu O = 15.99 g
Amu of H = 1.00 g
H2O = (2)1.01g + 16.00 = 1.02g = 18.0g
H2O
4. 1 mol H2O 18.0g
_________
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1 mol H2O = 18.0g H2O g
(
)
Goal #1.5
– Which has more atoms, 1.5 mole of Fe or
1.0 mole of H2O? Explain.
1. 1.5 mol
Fe
(
1 mol atoms
_________
1 mol Fe
)
=1.5 mol atoms
H2O = (2)hydrogen atoms + 1 oxygen atom = atoms total
2. 1.0 mol H2O
(
3 mol atoms
_________
1 mol H2O
)= 3 mol atoms
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Goal #2
• Which has more atoms, 1 mole of Fe or 1
mole of Cu? Explain.
1. 1 mol Fe
2. 1 mol Cu
(
23 atoms Fe
6.02x10
_________
1 mol Fe
(
)
23 atoms Cu
6.02x10
_________
1 mol Cu
= 6.02x1023
atoms Fe
)
= 6.02x1023
atoms Cu
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Goal #3
• Which has more moles, 10g Fe or 10g
H2O? Explain.
1. 10g Fe
(
)
1 mol Fe
_________
= 0.179 mol Fe = 0.18g Fe
55.845g Fe
1 mol H2O
2. 10g H2O _________
18.00g H2O
(
)
= 0.556 mol H2O
= 0.56g H2O
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Goal #4
• Which is more toxic, 1 mole of As or
10g As?
1. Look at periodic table.
2. Amu As = 74.92g
3. 1 mol As
(
)
74.92g As
_________
1 mol As
= 74.92 g As
4. 10.00g As
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Problem #1
• How many grams of calcium chloride,
CaCl2 are there in a sample of 10L at stp?
1. Amu Ca = 40.08g
2. Amu Cl = 35.45g
3. Amu CaCl2 = 40.08g + (2) 35.45g = 111g CaCl2
4. 10L CaCl2
1_________
mol CaCl2
22.4L CaCl2
(
)(
111g
CaCl2
_________
1 mol CaCl2
)
= 50g CaCl2
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Problem #2
• How many particles of magnesium chloride,
MgCl2 are there in 3g ?
1. Amu Mg = 24.30g
2. Amu Cl = 35.45g
3. Amu MgCl2 = 24.30g + (2) 35.45g = 95.2g MgCl2
4. 3g MgCl2
1_________
mol MgCl2
95.2g MgCl2
(
)(
23 particles MgCl
6.02x10
2
_________
1 mol MgCl2
= 1.90x1022 particles MgCl2
21
)
Check-in
• You have one mole of NaCl and one
mole of KCl. Which one weighs more?
Explain your thinking.
22
Wrap-up
• The atomic weight on the periodic table
is equivalent to the mass of 1 mole of
atoms of the element in grams.
• The molar mass of a compound is the
sum of the atomic weights of the atoms
in the compound.
• Molar mass allows you to convert
between moles and grams.
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