1
CH302
Exam 4 Practice Problems (buffers, titrations, Ksp)
Equilibrium Constants
The following equilibrium constants will be useful for some of the problems.
Substance
Constant
Substance
Constant
HCO
2
H
K
a
= 1.8
×
10
4
H
2
CO
3
K
1
= 4.2
×
10
7
HNO
2
K
a
= 4.5
×
10
4
K
2
= 4.8
×
10
11
HOCl
K
a
= 3.5
×
10
8
(COOH)
2
K
1
= 5.9
×
10
2
HF
K
a
= 7.2
×
10
4
K
2
= 6.4
×
10
5
HCN
K
a
= 4.0
×
10
10
CH
3
COOH
K
a
= 1.8
×
10
5
H
2
SO
4
K
1
= very large
C
6
H
5
NH
2
K
b
= 4.2
×
10
10
K
2
= 1.2
×
10
2
NH
3
K
b
= 1.8
×
10
5
HOBr
K
a
= 2.5
×
10
9
1.Refer to Equilibrium Constants. The nonionized form of an acid indicator is yellow, and its anion is blue. The
K
a
of this
indicator is 10
6
. What will be the approximate pH range over which this indicator changes color?
a. 35
d. 810
b. 46
e. 911
c. 57
2.Refer to Equilibrium Constants. The equivalence point of the titration of an unknown base with HCl is at pH = 5.90.
What would be the
K
a
for the
best
choice of an indicator for this titration?
a. 10
2
d. 10
6
b. 10
4
e. 10
7
c. 10
8
3.Refer to Equilibrium Constants. What is the pH at the point in a titration at which 20.00 mL of 1.000
M
KOH has been
added to 25.00 mL of 1.000
M
HBr?
a. 1.67
d. 2.71
b. 0.95
e. 1.22
c. 3.84
4.Refer to Equilibrium Constants. Which titration curve could describe the titration of a solution of HCl by addition of a
solution of KOH?
a.
b.
c.
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d.
e.
5.Refer to Equilibrium Constants. Which indicator could be used to titrate aqueous NH
3
with HCl solution?
Acid Range Color
pH Range
Basic Range Color
a.
pink
1.22.8
yellow
b.
blue
3.44.6
yellow
c.
yellow
6.57.8
purple
d.
colorless
8.39.9
red
e.
none of these indicators
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 Summer '10
 McCord
 pH, equilibrium constants

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