Introduction to the Mole and Molar Mass

1
Introduction to the Mole and Molar Mass

• Revised 9/05/06

2
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 cant 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.

3
Background

• When you buy eggs you usually ask for a _______
  eggs.
• You know that one dozen of any item is ______.

Dozen
12
4
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?

5

• What determines how many items should make up a
  particular unit?

6

• 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?

7
Materials

• 3 packages of different types of candy, balance,
  worksheet, calculator, pencil.

8
Part 1

• 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.

9
Data Table 1
Name of the Items in the Package Number of items in package Mass of the package
Jolly Ranchers
Caramels
Hershey's Kisses
26.9
4
4
23.03
20.96
4
10
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
• _____ items.

4
11
1. A DART of oranges will have _____ oranges.
4
12
2. A DART of pretzels has ____ pretzels.
4
13
3. A DART of molecules of water has ____
molecules of water.
4
14
4. A DART of particles has ___ particles.
4
15
5. A DART of atoms of iron has _____ atoms of
iron.
4
26 Fe 55.85
16
6. A DART of formula units of salt has _______
formula units of salt.
4
17
7. How many Hersheys Kisses are in 2 DARTS?
_______
8
18
8. How many caramels are in 10 DARTS? _______
40
19
9. How many Dum Dum Pops are in 400 DARTS? _______
1600
20
10. How many Starbursts are in 1/2 DART? _____
2
21
11. Write the directions for finding the number
of items if given the number of DARTS
22
12. How many oranges are in 5 DARTS? _______
20
23
13. How many apples are in 0.5 DARTS? _______
2
24
14. How many pencils are in 0.25 (1/4) DARTS? ___
1
25
15. How many atoms of silver are in 20 DARTS?
_______
80
47 Ag 107.9
26
16. How many molecules of water are in 5 DARTS?
_______
20
27

• 17. How many DARTS are 16 Hersheys Kisses? ______

4
28

• 18. How many DARTS are 100 pretzels? ____

25
29

• 19. How many DARTS are 400 Starbursts? ____

100
30

• 20. How many DARTS is 1 orange? ________
• (Write a fraction or a decimal.)

¼ 0.25
31

• 21. How many DARTS are 2 caramels? _____

0.5
32
22. Write your own directions for finding the
number of DARTS given the number of pieces
33
23. How many DARTS are 48 Hersheys Kisses? ____
12
34
24. How many DARTS are 32 Hersheys Kisses? ______
8
35
25. How many DARTS are 24 Jolly Ranchers? ______
6
36
26. How many DARTS are 2 Gobstoppers? ______
.5
37
27. How many DARTS are 20 caramels? ______
5
38
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.

39
One MOLE of anything has 602,200,000,000,000,000,0
00,000 items.
40
AVOGADROS NUMBER

• 6.022 x 1023
• One MOLE of anything has 6.022 x 1023 items.

41
28. How many Hersheys Kisses make up 1 MOLE?

• 6.022 x 1023

42
29. How many caramels make up 10 MOLES?

• 10 6.022 x 1023
• 60.22 x 1023
• Or
• 6.022 x 1024

43
30. Find the number of Jolly Ranchers in 4 MOLES.

• 4 6.022 x 1023
• 24.088 x 1023
• 2.41 x 1024

44
31. Find the number of atoms of sodium in 2
MOLES.

• 26.022 x 1023
• 12.044 x 1023
• 1.20 x 1024

11Na 22.99
45
32. Find the number of molecules of water in 6
MOLES.

• 66.022 x 1023
• 36.113 x 1023
• 3.61 x 1024

46
33. Find the number of caramels in 0.5 MOLES.

• .56.022 x 1023
• 3.011 x 1023

47
34. How many moles of caramels is 6.022x1023 of
caramels? ___
1
48
35. How many moles of Starbursts is 6.022x1023 of
Starbursts? ___
1
49
36. How many moles of Gobstoppers is 12.04x1023
of Gobstoppers? ___
2
12.04 x 1023 2 6.022 x 1023
50
37. How many atoms of potassium make up one MOLE?

• 6.022 x 1023

19 K 39.10
51
38. How many atoms of potassium make up 2 MOLES?

• 26.022 x 1023
• 12.044 x 1023
• 1.20 x 1024

19 K 39.10
52
39. How many molecules of water make up 1 MOLE?

• 6.022 x 1023

53
40. How many molecules of water make up 5 MOLES?

• 56.022 x 1023
• 30.110 x 1023
• 3.01 x 1024

54
41. How many moles are 6.022 x 1023 atoms of
sodium? _____
1
55
42. How many moles are 12.04 x 1023 atoms of
carbon? _____
2
12.04 x 1023 2 6.022 x 1023
56
43. How many moles are 18.06 x 1023 atoms of
sodium? _____
3
18.06 x 1023 3 6.022 x 1023
57
44. How many moles are 60.22 x 1023 atoms of
sodium? _____
10
60.22 x 1023 10 6.022 x 1023
58
45. How many moles are 6.022 x 1023 molecules of
water? _____
1
59
46. How many moles are 12.04 x 1023 molecules of
water? _____
2
12.04 x 1023 2 6.022 x 1023
60
47. How many moles are 30.10 x 1023 molecules of
water? _____
5
30.10 x 1023 5 6.022 x 1023
61
Part 2
62
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 Hersheys Kisses, Jolly Ranchers, and
  caramels.

63
Data Table 1
Name of the Items in the Package Number of items in package Mass of the package
Jolly Ranchers
Caramels
Hershey's Kisses
26.9
4
4
23.03
20.96
4
64
48. Based on your measurements, the mass of 1
DART of Hersheys Kisses is ______ g.
20.96
65
49. The mass of 2 DARTS of Hersheys Kisses is
______ g.
41.92
66
50. The mass of 1 DART of Jolly Ranchers is ___ g.
26.9
67
51. The mass of 1 DART of caramels is ____g
23.03
68
52. The mass of 100 DARTS of Hersheys Kisses is
____ g.
2096
69
53. The mass of 1/2 DART of Hersheys Kisses is
____ g.
10.48
70
54. Complete the directions for finding mass of
a given number of DARTS
71
55. The mass of 4 DARTS of Jolly Ranchers is ____
g.
107.6
72
56. The mass of 0.5 DARTS of Jolly Ranchers is
____ g.
13.45
73
57. The mass of 100 DARTS of caramels is _____ g.
2303.00
74
58. The mass of 1/5 DARTS of caramels is _____ g.
4.606
75
59. The mass of 60 DARTS of Hersheys Kisses is
_____ g.
1257.6
76
60. The mass of 0.1 DARTS of Hersheys Kisses is
_____ g.
2.096
77
61. How would you calculate the number of DARTS
if you know the mass of a package of Hersheys
Kisses?
260/20.96 12.40
78
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
79
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
80
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.

81
Periodic Table
82
64. The mass of 1 mole of Strontium (Sr) is ___ g.
87.62
38 Sr 87.62
83
65. The mass of 1 mole of Lead (Pb) is ____ g.
207.2
82 Pb 207.2
84
66. The mass of 1 mole of Nickel (Ni) is ____ g.
58.69
28 Ni 58.69
85
67. The mass of 4 moles of Strontium (Sr) is
_____g.
350.48
38 Sr 87.62
86
68. The mass of 0.5 moles of Lead (Pb) is ____ g.
103.6
82 Pb 207.2
87
69. The mass of 100 moles of (Ni) is _____ g.
5869.00
28 Ni 58.69
88
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.

89
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

90
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).

91
Potassium Permanganate KMnO4

• Potassium (K) 39.10 g/mole
• Manganese (Mn) 54.94g/mole
• Oxygen (O) 416.00 g/mole 158.04
  g/mole.

92
70. The molar mass of 1 mole of Sodium Chloride
(NaCl) is____ g.
58.44
93
71. The molar mass of 1 mole of Lead Iodide
(PbI2) is _____ g.
461.0
94
72. The mass of 100 moles of Nickel Sulfide (NiS)
is ________ g.
9076.00
95
73. The mass of 1 mole of is Glucose (C6H12O6) is
______ g.
180.156
96
74. The mass of 1 mole of is Sucrose (C12H24O12 )
_______ g.
306.31
97
75. The mass of 4 moles of Glucose (C6H12 O6) is
_________ g.
720.624
98
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.

99
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.

100
The three steps above can be expressed in the
following proportion

• Grams Moles
• --------------- --------------
• Molar Mass 1 Mole

101
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.

102
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.

103
Practice Problems
104
1. Calculate the moles present in2.00 grams of
H2O

• .11 moles water

105
2. Calculate the moles present in75.57 grams of
KBr

• .635 moles KBr

106
3. Calculate the moles present in100.0 grams of
KClO4

• .72 moles KClO4

107
4. Calculate the moles present in225.5 grams of
Sucrose (C12H24O12)

• .63 moles Sucrose

108
5. Calculate the moles present in350.0 grams of
Glucose (C6H12O6)

• 1.943 moles Glucose

109
Homework
110
1. Calculate the moles present in3.00 grams of
NaCl

• .05 moles

111
2. Calculate the moles present in25.0 grams of
NH3

• 1.47 moles NH3

112
3. Calculate the moles present in16.0 grams of
KCl

• .21 moles KCl

113
4. Calculate the moles present in30.25 grams of
BeCl2

• .38 moles KCl

114
5. Calculate the moles present in175.25 grams
of Li2S

• 3.81 moles Li2S

115
6. Calculate the moles present in75.62 grams of
CO2

• 1.72 moles CO2

116
7. Calculate the moles present in56.5 grams of
H2O

• 3.14 moles H2O

117
8. Calculate the moles present in22.6 grams of
CH3COOH

• .38 moles CH3COOH

118
9. Calculate the moles present in18.4 grams of
AgCl

• .13 moles AgCl

119
10. Calculate the moles present in 68.3 grams of
HCN

• 2.53 moles HCN