ekk86 – hw06 – Holcombe – (53570)
1
This
printout
should
have
25
questions.
Multiplechoice questions may continue on
the next column or page – find 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 find the solution, DO
NOT make any assumptions (i.e. USE THE
QUADRATIC FORMULA). Also, be sure to
enter excess significant figures 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 di
ff
erent concentrations
of H
+
.
Therefore, they will have di
ff
erent
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% o
ff
.
C
2
H
5
OCOOH + H
2
O
Initial
0.06
Final
0
.
06

x
C
2
H
5
OCOO

+ H
3
O
+
Initial


Final
x
x
K
a
=
C
2
H
5
OCOO

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

x
= 8
.
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
a c
2
a
Since
b
2

4
a c
=
(

8
.
4
×
10

4
)
2

4 (1)
(

5
.
04
×
10

5
)
= 2
.
02
×
10

4
,
then
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
ekk86 – hw06 – Holcombe – (53570)
2
x
=
(

8
.
4
×
10

4
)
±
√
2
.
02
×
10

4
2 (1)
= (0
.
00669
,

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

log H
3
O
+
=

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
= 0
.
1 M
pH = 1
.
2
Analyzing the reaction with molarities,
HClO
2
+ H
2
O
H
3
O
+
+ ClO

2
0
.
1

0
0

x

x
x
0
.
1

x

x
x
[H
3
O
+
] = [ClO

2
] = 10

pH
= 10

1
.
2
= 0
.
0630957 mol
/
L
The
K
a
is
K
a
=
[H
3
O
+
][ClO

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

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

log(0
.
107876) = 0
.
967077
.
This is the end of the preview.
Sign up
to
access the rest of the document.
 Spring '07
 Holcombe
 Chemistry, pH, Ka HCl, OCOOH

Click to edit the document details