Version 161 – Exam One: Shear – Shear – (52375)
1
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printout
should
have
30
questions.
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before answering.
001
12.0 points
When the reaction
P
4
O
10
+ KOH
→
K
3
PO
4
+ H
2
O
is balanced, how much KOH is required to
react with 3 moles of P
4
O
10
?
1.
27 mol
2.
18 mol
3.
36 mol
correct
4.
9 mol
5.
3 mol
Explanation:
n
P
4
O
10
= 3.0 mol
The balanced chemical equation for this
reaction is
P
4
O
10
+ 12 KOH
→
4 K
3
PO
4
+ 6 H
2
O
.
From the coefficients we see that 12 mol KOH
are required for each mole of P
4
O
10
reacted.
We use this ratio to calculate the moles of
KOH required to react 3 mol P
4
O
10
:
? mol KOH = 3 mol P
4
O
10
×
12 mol KOH
1 mol P
4
O
10
= 36 mol KOH
002
10.0 points
An electron in a hydrogen atom could un
dergo any of the transitions listed below, by
emitting light.
Which transition would give
light of the shortest wavelength? Hint: Think
Planck, remember Bohr. You may also want
to think about the Rydberg equation, but it
is not necessary to do the calculations.
1.
n
= 4 to
n
= 1
correct
2.
n
= 3 to
n
= 1
3.
n
= 2 to
n
= 1
4.
n
= 4 to
n
= 2
5.
n
= 4 to
n
= 3
Explanation:
Photons
with
shorter
wavelengths
have
more energy than those with longer wave
lengths.
n
= 1 is the lowest energy level, the
energy increases as n increases. A transition
from
n
= 4 to
n
= 1 will release more energy
than any other option given.
003
10.0 points
The photoelectric effect provided evidence for
the (wave, particle)like behavior of light. The
phenomenon of diffraction provided evidence
for the (wave, particle)like behavior of light.
1.
wave, particle
2.
wave, wave
3.
particle, wave
correct
4.
particle, particle
Explanation:
The photoelectric effect demonstrates par
ticle behavior and diffraction wave behavior.
004
12.0 points
Radio station KLBJ broadcasts at a frequency
of 93
.
7
×
10
6
s
−
1
. Determine the length of the
waves that corresponds to this frequency.
1.
2
×
10
−
8
m
2.
2 nm
3.
93.7 m
4.
3.20 nm
5.
3.20 m
correct
Explanation:
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Version 161 – Exam One: Shear – Shear – (52375)
2
005
12.0 points
The
molecular
formula
for
ethyl
chloride
(C
2
H
5
Cl).
What is the molecular weight of
ethyl chloride?
1.
48.5 grams/mol
2.
69.5 grams/mol
3.
64.5 grams/mol
correct
4.
8 grams/mol
5.
34.0 grams/mol
Explanation:
The formula weight of a compound is based
on the atomic weights of the elements in the
compound.
Each mole of C
2
H
5
Cl contains 2 mol of
C, 5 mol of H, and 1 mol of Cl.
We know
the atomic masses of each of these elements
from the periodic table.
Using these atomic
masses we calculate the grams of each of these
elements in one mole of C
2
H
5
Cl:
m
C
= 2 mol C
×
12
.
01 g C
1 mol C
= 24
.
02 g C
m
H
= 5 mol H
×
1
.
01 g H
1 mol H
= 5
.
05 g H
m
Cl
= 1 mol Cl
×
35
.
45 g Cl
1 mol Cl
= 35
.
45 g Cl
To get the mass of one mole of C
2
H
5
Cl we add
the masses of the component parts.
This is
the formula weight:
FW
C
2
H
5
Cl
= 24
.
02 g + 5
.
05 g + 35
.
45 g
=
64
.
52 g C
2
H
5
Cl
mol C
2
H
5
Cl
006
12.0 points
Propane (C
3
H
8
) burns in oxygen to produce
carbon dioxide and water. What is the correct
form of the chemical equation that describes
this reaction?
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 Spring '08
 wandelt
 Chemistry, Atom, Reaction, mol KOH

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