Radioactive Decay And Acid Dissociation Constant Chap. 9 And 10 Worksheet With Answers - Middle Tennessee State University Page 13
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20Solution
In this single replacement
reaction, sodium and hydrogen exchange places. The resulting sodium
hydroxide is a strong base.
SOLUTIONS TO CHEMISTRY FOR THOUGHT
9.132 In an early industrial method, H
SO
was manufactured in lead-lined chambers.
2
4
Propose an explanation for this.
Solution
Pb reacts with H
SO
to make PbSO
and H
. The PbSO
is not soluble and
2
4
4
2
4
coats the surface of the lead, preventing further reaction between the acid
and the metal.
-
-2
9.133 A saturated solution of solid Ca(OH)
in water has a [OH
] of only 2.50 x 10
M,
2
and yet Ca(OH)
is a strong base. Explain this apparent contradiction.
2
Solution
Ca(OH)
is only slightly soluble in water, but the limited amount of Ca(OH)
2
2
which dissolves is completely ionized (completely dissociated). Hence, it is a
-
strong base because it ionizes completely, but the concentration of [OH
] is
limited by the solubility.
9.134 Imagine a solution of weak acid is being titrated with a strong base. Describe the
substances present in the solution being titrated when it has been titrated
halfway to the equivalence point. How is the pH of this half-titrated solution
related to pK
for the weak acid?
a
Solution
At that point in the titration of HB, one half of the original HB has reacted to
-
form B
. Thus, the remaining concentration of HB equals the concentration of
-
[B
]
log
= 0
-
B
. Using Equation 9.54, the pH = pK
because
[HB]
a
9.135 Calculate K
for the following weak acids based on the equilibrium
a
concentrations and pH values given.
a) Benzoic acid, represented by HBz:
-
-3
pH = 2.61, [Bz
] = 2.48 x 10
, [HBz] = 0.0975
b) Abietic acid, represented by HAb:
-
-5
pH = 4.16, [Ab
] = 6.93 x 10
, [HAb] = 0.200
c) Cacodylic acid, represented by HCc:
-
pH = 3.55, [Cc
] = 0.000284, [HCc] = 0.150
Solution
-
[B
]
pK
= pH- log
Rearranging Equation 9.54 gives
a
[HB]
- 3
[2.48 x10
]
- 5
pK
= 2.61- log
= 4.20
K
= 6.93 x10
a
a
a)
[0.0975]
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