Moles and Molar Mass

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Moles and Molar Mass
Chemistry
Learning Objectives
• TLW define and use the concept of a mole
(TEKS 8.A)
• TLW use the mole concept to calculate the
number of atoms, ions, and molecules in a
sample of material (TEKS 8.B)
• TLW manipulate chemical quantities using
dimensional analysis (TEKS 2.G)
Background
• As you might imagine, we will not be able to measure the
mass or volume of individual atoms, ions, or molecules in the
Chemistry Lab.
• Molecules are so small that a single drop of water contains
billions and billions of them.
• Just like eggs are grouped in dozens, and other items are
grouped in grosses, reams, etc… atoms and molecules are
grouped in moles. (not be confused with the fury little
creature that lives underground)
• We may not be able to measure the mass of one water
molecule in lab, but we can measure the mass of one mole of
water molecules.
Mole Day Song
• Link to YouTube
A. What exactly is a mole?
1. A counting number
2. The SI unit for amount of particles
3. Like all units, a mole has to be based on something
reproducible. A mole is the quantity of anything
that has the same number of particles found in 12.000
grams of carbon-12
4. 1 mol = 6.022 X 1023 items (atoms, ions, molecules)
5. Referred to as Avogadro’s Number
How large is large? Mole Analogies
1 mole of basketballs would fill a
bag the size of the earth!!
Counting every grain of sand in
the desert!!
• A mole of marshmallows would cover the
planet Earth 12 miles high
• Computers can count at the rate of over
800 million counts per second. At this rate
it would take a computer over 25 million
years to count to 6.02 x 1023
• 1 mole of marbles would fill the entire
Grand Canyon and there would still be
enough left over to displace all the water in
Lake Michigan and a few other lakes!
• A mole of hockey pucks would be equal to
the mass of the Moon.
• Assuming that each human being has 60
trillion body cells (6.0 x 1013) and the
Earth's population is 6 billion (6 x 109), the
total number of living human body cells on
the Earth at the present time is 3.6 x 1023
or a little over half of a mole.
Activity for Mole Concept
• Link
Activity Follow up Discussion
– If one mole of pennies were divided up among the Earth's population
of 6 billion people, each person would receive 1 x 1014 pennies = 1 x
1012 dollars ($1 TRILLION dollars)
• Personal spending at the rate of one million dollars a day would
use up each person’s wealth in about 2,740 years.
– If you have 6.022 x 1023 pennies and you spend $1 million dollars
each day it would take you 1.65 x 1012 years to spend all
– Life would not be comfortable because the surface of the Earth
would be covered in copper coins to a depth of nearly 900 meters
(nearly 9 football fields deep).
B. Molar Mass
1. The mass of 1 mole of a pure
substance is called the
molar mass (see periodic table)
2. Atomic mass tells
a. atomic mass units per
atom (amu)
b. grams per mole (g/mol)
3. Molar mass is usually rounded
to two decimal places
4. Ex. of Molar mass
carbon
12.01 g/mol
aluminum 26.98 g/mol
zinc
65.39 g/mol
5. A molar mass of an element
contains 1 mole of atoms
carbon’s mole’s mass is 12.01g
6. MOLAR MASS EQUALS
ATOMIC MASS
C. What about the molar mass of
molecules and compounds?
1. Water – H2O
molar mass: 2(1.01) + 16.00 =
18.02 g/mol
2. Sodium chloride = NaCl
molar mass: 22.99 + 35.45 =
58.44 g/mol
3. sucrose = C12H22O11
molar mass:
12(12.01) + 22(1.01) + 11(16.00)
= 342.34 g/mol
D. Molar Conversions
1. How many moles of carbon are in
26 g of carbon?
26 g 1 mol C
= 2.2 mol C
12.01 g C
The molar mass of Carbon
2. How many molecules are in 2.50
moles of C12H22O11?
2.50 mol
6.022 
23
10
molecules
1 mol
 1024 molecules of
C12H22O11
= 1.51
3. How many grams in 3.7 moles
of Silicon?
3.7 mol Si 28.09 g Si
= 103.93 g Si
1 mol Si
4. How many moles are in 15 g of
H2O?
…..1st find the molar mass of H2O
H = 1.01 g/mol
O = 16.00 g/mol
= 2(1.01) + 16.00
= 18.02 g per mole H2O
15g
1 mol
18.02 g
= .83 mol H2O
Group Practice
1. a) 20.0 g of Fe equals ___ moles
20.0 g Fe 1 mol
= .36 mol Fe
55.85 g Fe
b)19.7 g of Mg equals ___ moles
19.7 g Mg 1 mol
= .81 mol Mg
24.31 g Mg
Group Practice
2. a) 100.0 g of FeCl equals ___ moles
100.0 g 1 mol
= 1.10 mol FeCl
91.30 g FeCl
b)40.00 g of CO2 equals ___ moles
40.00 g 1 mol
= .91 mol CO2
44.01 g CO2
3. a) 0.356 moles of Al is how many g?
0.356 mol
26.98 g Al
1 mol
= 9.60 g Al
b) 0.56 moles of Ne is how many g?
0.56 mol
20.18 g Ne
1 mol
= 11.30 g Ne
4. a) 0.50 moles of Al2O3 is how many g?
0.50 mol
101.96 g Al2O3 = 50.98 g
1 mol
Al2O3
b) 2.6 moles of HF is how many g?
2.6 mol
20.01 g HF = 52.03 g HF
1 mol
5. a) 0.50 moles of Na is how many molecules?
0.50 mol
6.022 x 1023 molecules
1 mol
= 3.01 x 1023
molecules
b) 2.1 moles of HF is how many molecules?
2.1 mol
6.022 x 1023 molecules
1 mol
= 1.26 x 1024
molecules
6. a) How many moles are in 4.5 x 1024
molecules of Cr?
4.5 x 1024 molecules
1 mol
=
7.5 moles Cr
6.022 x 1023 molecules
b) How many moles are in 3 x 1026 molecules of Cr2O3?
3 x 1026 molecules
1 mol
6.022 x 1023 molecules
= 498 moles
Cr2O3
7. a) How many molecules of Cr are in 30.1 g?
30.1 g Cr
1 mol
6.022 x 1023 molecules
=
52.00 g
1 mol
3.49 x 1023
molecules Cr
b) How molecules of Fe2O3 in 2,500 g?
2,500 g
1 mol
159.70 g
6.022 x 1023 molecules
1 mol
= 9.43 x 1024
molecules
Fe2O3
Factoid to Remember
• Subscripts indicate moles
H2
• When we move to balancing chemical
equations moles = coefficients
2H2 + O2  2H2O
Independent Practice
• Calculations – Set 1
• Calculations – Set 2
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