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100 Chapter 2
Copyright © 2017 Pearson Education, Inc.
39.
If the pH of the solution is less than the compound’s
p
K
a
value, the compound will be in its acidic form
(with its proton).
If the pH of the solution is greater than the compound’s
p
K
a
value, the compound will be in its basic form
(without its proton).
a.
CH
3
COO
-
b.
3 2 3
CH CH NH
+
c.
H
2
O
d.
Br
-
e.
4
NH
+
f.
HC N
g.
NO
2
-
h.
NO
3
-
i.
HONH
2
40.
pH 10.4
(As long as the pH is greater than the
p
K
a
of the compound, at least 50% of the compound will be in its
basic form.)
41.
Solved in the text.
42.
a. 1.
charged
2.
charged
3.
charged
4.
charged
5.
neutral
6.
neutral
b. 1.
neutral
2.
neutral
3.
neutral
4.
neutral
5.
neutral
6.
neutral
43.
a.
The
+
NH
3
group withdraws electrons, which increases the acidity of the COOH group.
b.
Both the COOH group and the
+
NH
3
group will be in their acidic forms, because the pH of the solution
is less than both of their
p
K
a
values.
C
O
OH
CH
3
CH
NH
3
+
c.
The COOH group will be in its basic form because the pH of the solution is greater than its
p
K
a
.
The
+
NH
3
group will be in its acidic form because the pH of the solution is less than its
p
K
a
.
C
O
O
CH
3
CH
NH
3
−
+
d.
Both the COOH group and the
+
NH
3
group will be in their basic forms because the pH of the solution
is greater than both of their
p
K
a
values.
C
O
O
CH
3
CH
NH
2
−
e.
No, alanine can never be without a charge. To be without a charge would require a group with a
p
K
a
value of 9.69 to lose a proton before a group with a
p
K
a
value of 2.34. This clearly cannot happen. A
weak acid cannot have a greater tendency to lose a proton than a strong acid has.