Chemistry Reference
In-Depth Information
Answer Key
The actual answers will be shown in brackets, followed by the explana-
tion. If you don't understand an explanation that is given in this section, you
may want to go back and review the lesson that the question came from.
Lesson 7-1 Review
1.
[24.0 g]—6.94 g + 16.0 g + 1.01 g = 24.0 g
2.
[155.5 g]—63.5 g + 2(14.0 g) + 4(16.0 g) = 155.5 g
3.
[68.2 g]—2(14.0 g) + 8(1.01 g) + 32.1 g = 68.2 g
4.
[6.02 × 10
23
molecules]—Just as one dozen of anything represents 12 items,
one mole of anything represents 6.02 x 10
23
items.
5.
[1.81 × 10
24
atoms]—This is a “parts” question. Just as one dozen cars has
more than one dozen tires, one mole of molecules has more than one mole
of atoms. Each water molecule contains three atoms, so one dozen water
molecules would contain 3(12) = 36 atoms. One mole of water molecules
contains 3(6.02 × 10
23
) = 1.81 × 10
24
atoms. It may help to see the work
with all of the units, as shown here:
1 mole × (
6.02 × 10
23
molecules
moles
3 atoms
molecule
)
= 3(6.02 × 10
23
) atoms
= 1.81 × 10
24
atoms
) × (
6.
[2.41 × 10
24
molecules]—Four dozen doughnuts would be 4(12) = 48
doughnuts. Four moles of CH
4
represents 4(6.02 × 10
23
) = 2.41 × 10
24
molecules.
7.
[1.20 × 10
25
atoms]—Each molecule of CH
4
represents five atoms, so four
moles of molecules would contain 5 × 4(6.02 × 10
23
) atoms, as shown here.
6.02 × 10
23
molecules
mole
5 atoms
molecule
= 1.20 × 10
25
atoms
4 moles ×
×
Lesson 7-2 Review
1.
Volume of nitrogen = 4.50 moles ×
22.4 dm
3
mole
[101 dm
3
]—
= 101 dm
3
2.
[257 g]—Molar mass of NaBr is 102.9 g/mole (23.0 g + 79.9 g).
Mass of NaBr = 2.50 moles ×
102.9 g
mole
= 257 g
3.
[4.17 moles]—Molar mass of carbon = 12.0 g/mole
# of moles of carbon =
mass of sample
molar mass
50.0 g
12.0 g/mole
= 4.17 moles
=
4.
[1.13 × 10
24
molecules]—
# of molecules = # of moles × Avogadro's number
6.02 × 10
23
molecules
mole
= 1.13 × 10
24
molecules
= 1.88 moles ×
volume of gas
molar volume
75.0 dm
3
22.4 dm
3
/mole
= 3.35 moles
5.
[3.35 moles]—
# of moles =
=
