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ekk86 – hw06 – Holcombe – (53570)
1
This printout should have 25 questions.
Multiplechoice questions may continue on
the next column or page – fnd all choices
beFore answering.
PLEASE NOTE: Due to the tolerances on
numerical problems (your answer must be
within ONE PERCENT oF the correct answer
unless otherwise noted), iF a problem requires
the quadratic Formula to fnd the solution, DO
NOT make any assumptions (i.e. USE THE
QUADRATIC ±ORMULA). Also, be sure to
enter excess signifcant fgures to assure that
you are not penalized For rounding.
001
10.0 points
Solution A contains HCl and has an H
+
con
centration oF 10

3
M. Solution B contains
CH
3
COOH and has an H
+
concentration oF
10

5
M. Which solution is more acidic and
which solution has a greater pH?
1.
Solution A is more acidic, but Solution B
has a greater pH.
correct
2.
Both solutions have identical acidities and
pH.
3.
Solution B is more acidic, but Solution A
has a greater pH.
4.
Solution A is more acidic and has a greater
pH.
5.
Solution B is more acidic and has a greater
pH.
Explanation:
[H
+
]
A
= 10

3
M
[H
+
]
B
= 10

5
M
pH =

log[H
+
]
The solutions have di²erent concentrations
oF H
+
.
ThereFore, they will have di²erent
acidities and pH. The more concentrated will
be more acidic and have a lower pH.
002
10.0 points
The buildup oF lactic acid in muscles causes
pain during extreme physical exertion. The
K
a
For lactic acid (C
2
H
5
OCOOH) is 8
.
4
×
10

4
. Calculate the pH oF a 0
.
06 M solution
oF lactic acid.
1.
6.348
2.
2.174
correct
3.
2.149
4.
3.533
5.
11.851
6.
2.043
7.
2.297
8.
1.926
Explanation:
K
a
=8
.
4
×
10

4
[C
2
H
5
OCOOH] = 0
.
06
You MUST use the quadratic Formula to
solve this one. IF you use the approximation,
your answer will be more than 5% o².
C
2
H
5
OCOOH + H
2
O
±
²
Initial
0.06
±inal
0
.
06

x
C
2
H
5
OCOO

+H
3
O
+
Initial

±inal
xx
K
a
=
±
C
2
H
5
OCOO

²±
H
3
O
+
²
[C
2
H
5
OCOOH]
=
x
2
0
.
06

x
.
4
×
10

4
x
2
+8
.
4
×
10

4
x

5
.
04
×
10

5
=0
To solve the quadratic equation,
x
=

b
±
√
b
2

4
ac
2
a
Since
b
2

4
=
(

8
.
4
×
10

4
)
2

4 (1)
(

5
.
04
×
10

5
)
=2
.
02
×
10

4
,
then
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View Full Documentekk86 – hw06 – Holcombe – (53570)
2
x
=
(

8
.
4
×
10

4
)
±
√
2
.
02
×
10

4
2 (1)
= (0
.
00669
,

0
.
00753)
,
x
=
±
H
3
O
+
²
=0
.
00669, so
pH =

log
±
H
3
O
+
²
=

log(0
.
00669)
=2
.
174
003
10.0 points
The pH of 0
.
1 M HClO
2
(chlorous acid)
aqueous solution was measured to be 1
.
2.
What is the value of p
K
a
for chlorous acid?
1.
1.20
2.
0.96
correct
3.
0.11
4.
1.40
5.
3.91
6.
2.57
Explanation:
M
.
1 M
pH = 1
.
2
Analyzing the reaction with molarities,
HClO
2
+H
2
O
±
²
H
3
O
+
+ ClO

2
0
.
1

00

x

xx
0
.
1

x

[H
3
O
+
] = [ClO

2
] = 10

pH
= 10

1
.
2
.
0630957 mol
/
L
The
K
a
is
K
a
=
[H
3
O
+
][ClO

2
]
[HClO
2
]
=
(0
.
0630957)
2
0
.
1

0
.
0630957
.
107876
and the p
K
a
is
p
K
a
=

log(0
.
107876) = 0
.
967077
.
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 Spring '07
 Holcombe
 Chemistry

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