Introduction to the
Mole and Molar
Mass
Revised 9/05/10
Purpose
At the completion of this unit students will
• Have a conceptual understanding of the mole as the
method of “counting” items and finding the mass of items
that can’t be seen.
• Be able to calculate the number of items (molecules,
atoms, ions, and formula units) if given the number of
moles.
• Be able to calculate the number of moles if given the
number of items.
• Be able to calculate the mass of a sample if given the
number of moles in a sample.
• Be able to calculate the number of moles in a sample if
given the mass of a sample.
• Be able to prepare a sample containing a given number of
moles.
• Be able to determine the molar mass of a compound.
Background
• When you buy eggs you usually
Dozen eggs.
ask for a _______
• You know that one dozen of any
item is ______.
12
Paper
• Paper is packaged by a ream.
• A ream of paper has 500 sheets.
• Why is it useful to use units like a
dozen or a ream?
• What determines how many items
should make up a particular unit?
• If you were asked to design a new
unit to count something, what
would you consider when
choosing how many items should
be included in your new counting
unit?
Materials
• 3 packages of different types of
candy, balance, worksheet,
calculator, pencil.
Part 1
1.
2.
3.
4.
Record the number of items in each package.
Measure the mass of each package. Record the
mass of each package in the data table.
Answer questions in Analysis and
Interpretations.
Record masses your group measured on the
board summarizing class data.
Data Table 1
Name of the
Items in the
Number of items
in package
Mass of the
package
Package
Jolly
Ranchers
Caramels
Hershey's
Kisses
4
26.9
4
23.03
4
20.96
ANALYSIS AND
INTERPRETATION
• As you know, a dozen represents 12 items.
• Since I did not have enough items to make
a dozen, I decided to make a new counting
unit. I called this unit an DART. Each of
your packages contains
4 items.
_____
1. A DART of oranges
4
will have _____
oranges.
2. A DART of pretzels
4
has ____ pretzels.
3. A DART of molecules
of water has ____
4
molecules of water.
4. A DART of particles
4 particles.
has ___
5. A DART of atoms of
4
iron has _____ atoms
of iron.
26
Fe
55.85
6. A DART of formula
units of salt has
4
_______
formula units
of salt.
7. How many Hershey’s
Kisses are in 2 DARTS?
8
_______
8. How many caramels
are in 10 DARTS?
40
_______
9. How many Dum
Dum Pops are in 400
1600
DARTS? _______
10. How many
Starbursts are in 1/2
2
DART? _____
11. Write the directions
for finding the number
of items if given the
number of DARTS
12. How many oranges are
20
in 5 DARTS? _______
13. How many apples are
2
in 0.5 DARTS? _______
14. How many pencils
are in 0.25 (1/4)
1
DARTS? ___
15. How many atoms of
silver are in 20
80
DARTS? _______
47
Ag
107.9
16. How many
molecules of water are
20
in 5 DARTS? _______
17. How many DARTS are 16
4
Hershey’s Kisses? ______
18. How many DARTS are
25
100 pretzels? ____
19. How many DARTS are
100
400 Starbursts? ____
20. How many DARTS
¼ 0.25
is 1 orange? ________
(Write a fraction or a decimal.)
21. How many DARTS
0.5
are 2 caramels? _____
22. Write your own
directions for finding
the number of DARTS
given the number of
pieces
23. How many DARTS
are 48 Hershey’s
12
Kisses? ____
24. How many DARTS
are 32 Hershey’s
8
Kisses? ______
25. How many DARTS
are 24 Jolly Ranchers?
6
______
26. How many DARTS are
.5
2 Gobstoppers? ______
27. How many DARTS
5
are 20 caramels? ______
DARTS
• DART of molecules of water
would be too small to see.
• Scientists had to select a bigger
unit for counting molecules of
substances.
• The unit scientists use is called a
MOLE.
One MOLE of
anything has
602,200,000,000,000,000,000,000
items.
AVOGADRO’S
NUMBER
•6.022 x
23
10
• One MOLE of anything
23
has 6.022 x 10 items.
28. How many
Hershey’s Kisses make
up 1 MOLE? 6.022 x 1023
29. How many caramels
make up 10 MOLES?
10 [6.022 x
6.022 x
23
10 ]
24
10
30. Find the number of
Jolly Ranchers in 4
MOLES.
4 [6.022 x
2.41 x
23
10 ]
24
10
31. Find the number of
atoms of sodium in 2
MOLES.
11
Na
22.99
2[6.022 x
1.20 x
23
10
24
10
]
32. Find the number of
molecules of water in 6
MOLES.
23
6[6.022 x 10 ]
3.61 x
24
10
33. Find the number of
caramels in 0.5
MOLES.
23
10
.5[6.022 x
]
23
3.011 x 10
34. How many moles of
23
caramels is 6.022x10
1
of caramels? ___
35. How many moles of
23
Starbursts is 6.022x10
1
of Starbursts? ___
36. How many moles of
24
Gobstoppers is 1.204x10
2
of Gobstoppers? ___
1.204 x 1024
6.022 x 1023
=2
37. How many atoms of
potassium make up one
MOLE? 6.022 x 1023
19
K
39.10
38. How many atoms of
potassium make up 2
MOLES?
19
K
39.10
2[6.022 x
1.20 x
23
10
24
10
]
39. How many
molecules of water
make up 1 MOLE?
6.022 x
23
10
40. How many
molecules of water
make up 5 MOLES?
23
5[6.022 x 10 ]
3.01 x
24
10
41. How many moles
23
are 6.022 x 10 atoms
1
of sodium? _____
42. How many moles
24
are 1.204 x 10 atoms
of carbon? 2_____
1.204 x 1024 = 2
6.022 x 1023
43. How many moles
24
are 1.806 x 10 atoms
3
of sodium? _____
1.806 x 1024 = 3
6.022 x 1023
44. How many moles
24
are 6.022 x 10 atoms
10
of sodium? _____
6.022 x 1024 = 10
6.022 x 1023
45. How many moles are
23
6.022 x 10 molecules
1
of water? _____
46. How many moles are
24
1.204 x 10 molecules
2
of water? _____
1.204 x 1024 = 2
6.022 x 1023
47. How many moles are
24
3.010 x 10 molecules
5
of water? _____
3.010 x 1024 = 5
6.022 x 1023
Part 2
Mass
• In addition to being able to tell the
number of items in an DART, you
can now tell the mass of an DART
of Hershey’s Kisses, Jolly
Ranchers, and caramels.
Data Table 1
Name of the
Items in the
Number of items
in package
Mass of the
package
Package
Jolly
Ranchers
Caramels
Hershey's
Kisses
4
26.9
4
23.03
4
20.96
48. Based on your
measurements, the mass
of 1 DART of Hershey’s
20.96 g.
Kisses is ______
49. The mass of 2
DARTS of Hershey’s
41.92 g.
Kisses is ______
50. The mass of 1 DART
of Jolly Ranchers is 26.9
___ g.
51. The mass of 1 DART
of caramels is 23.03
____g
52. The mass of 100
DARTS of Hershey’s
2096 g.
Kisses is ____
53. The mass of 1/2
DART of Hershey’s
10.48 g.
Kisses is ____
54. Complete the
directions for finding
mass of a given number
of DARTS
55. The mass of 4
DARTS of Jolly
107.6 g.
Ranchers is ____
56. The mass of 0.5
DARTS of Jolly
13.45 g.
Ranchers is ____
57. The mass of 100
DARTS of caramels is
2303.00
_____ g.
58. The mass of 1/5
DARTS of caramels is
4.606
_____ g.
59. The mass of 60
DARTS of Hershey’s
1257.6 g.
Kisses is _____
60. The mass of 0.1
DARTS of Hershey’s
2.096 g.
Kisses is _____
61. How would you
calculate the number of
DARTS if you know the
mass of a package of
Hershey’s Kisses?
260/20.96 = 12.40
62. How would you
calculate the number of
DARTS if you know
the mass of a package
of caramels?
198.5/23.03 = 8.62
63. How would you
calculate the number of
DARTS if you know the
mass of a package of
Jolly Ranchers?
198/26.9 = 7.36
Molar Mass
• Scientists use the Periodic Table
to determine the mass of a mole of
atom of an element.
• For example, a mole of Iron (Fe)
atoms would have a mass of
55.85g.
Periodic Table
64. The mass of 1 mole of
87.62 g.
Strontium (Sr) is ___
38
Sr
87.62
65. The mass of 1 mole
207.2 g.
of Lead (Pb) is ____
82
Pb
207.2
66. The mass of 1 mole of
Nickel (Ni) is ____
58.69 g.
28
Ni
58.69
67. The mass of 4 moles
of Strontium (Sr) is
350.48
_____g.
38
Sr
87.62
68. The mass of 0.5 moles
of Lead (Pb) is ____
103.6 g.
82
Pb
207.2
69. The mass of 100 moles
of (Ni) is _____
5869.00g.
28
Ni
58.69
Molar Mass
• Scientists also use the Periodic Table
to determine the molar mass (formula
weight) of compounds.
• The molar mass of the compound is
the sum of the molar masses of the
elements that make up the compound.
Potassium Chloride
• The molar mass of Potassium
Chloride is:
Potassium (K) 39.10 g/mole
Chloride (Cl) +34.45 g/mole
73.55 g/mole
Potassium Permanganate
• The molar mass of KMnO4 is the
sum of all the molar masses times
the number of atoms of each
element for the molecule
(subscript).
Potassium Permanganate
KMnO4
• Potassium (K)
39.10 g/mole
• Manganese (Mn) 54.94g/mole
• Oxygen (O)
4[16.00 g/mole]
158.04 g/mole.
70. The molar mass of 1
mole of Sodium Chloride
(NaCl) is____
58.44 g.
71. The molar mass of 1
mole of Lead Iodide
461.0 g.
(PbI2) is _____
72. The mass of 100
moles of Nickel Sulfide
9076.00 g.
(NiS) is ________
73. The mass of 1 mole
of is Glucose (C6H12O6)
180.156 g.
is ______
74. The mass of 1 mole of
is Sucrose (C12H24O12 )
306.31 g.
_______
75. The mass of 4 moles
of Glucose (C6H12 O6) is
_________
720.624 g.
Mole Conversions
• In chemistry, the mole is the standard
measurement of amount.
• However, balances DO NOT give readings
in moles. Balances give readings in grams.
• So the problem is that, while we compare
amounts of one substance to another using
moles, we must also use grams, since this
is the information we get from balances.
There are three steps to converting
grams of a substance to moles.
1. Determine how many grams are
given in the problem.
2. Calculate the molar mass of the
substance.
3. Divide step one by step two.
The three steps above can be
expressed in the following
proportion:
Grams
--------------Molar Mass
=
Moles
-------------1 Mole
Example #1 - Convert 25.0 grams
of KMnO4 to moles.
Step One: The problem will tell you how many grams are
present. Look for the unit of grams. The problem gives us
25.0 grams.
Step Two: You need to know the molar mass of the substance.
The molar mass of KMnO4 is 158.034 grams/mole.
Potassium (K)
=
39.10 x 1
=
39.10 g
Manganese (Mn)
=
54.94 x 1
=
54.94 g
Oxygen (O)
=
16.00 x 4
=
64.00 g
--------------158.04 g
Step Three: You divide the grams given by the substance's
molar mass (25.0/158.04)
The answer of 0.16 mole has been rounded off.
Example #2 - Calculate how
many moles are in 57.0 grams of
Mg(NO3)2
Step One: 57.0 grams are given in the text of the
problem.
Step Two: The molar mass is 148 grams/mole.
Mg (Magnesium) =
24 x 1=
24 g
N (Nitrogen)
= 14 x 2=
28 g
O (Oxygen)
=
16 x 6=
96 g
Step Three: Again you divide the grams by the
substances molar mass (57.0 g/148 g).
This answer has been rounded to 0.39 moles.
Practice
Problems
1. Calculate the moles present in:
2.00 grams of H2O
.11 moles water
2. Calculate the moles present in:
75.57 grams of KBr
.635 moles KBr
3. Calculate the moles present in:
100.0 grams of KClO4
.72 moles KClO4
4. Calculate the moles present in:
225.5 grams of
Sucrose (C12H24O12)
.63 moles Sucrose
5. Calculate the moles present in:
350.0 grams of
Glucose (C6H12O6)
1.943 moles Glucose
Homework
1. Calculate the moles present in:
3.00 grams of NaCl
.05 moles
2. Calculate the moles present in:
25.0 grams of NH3
1.47 moles NH3
3. Calculate the moles present in:
16.0 grams of KCl
.21 moles KCl
4. Calculate the moles present in:
30.25 grams of BeCl2
.38 moles KCl
5. Calculate the moles present in:
175.25 grams of Li2S
3.81 moles Li2S
6. Calculate the moles present in:
75.62 grams of CO2
1.72 moles CO2
7. Calculate the moles present in:
56.5 grams of H2O
3.14 moles H2O
8. Calculate the moles present in:
22.6 grams of CH3COOH
.38 moles CH3COOH
9. Calculate the moles present in:
18.4 grams of AgCl
.13 moles AgCl
10. Calculate the moles present
in: 68.3 grams of HCN
2.53 moles HCN