1
1
Ammonium nitrate is used in fertilizers.
Calculate
the pH of a 0.15 M solution of NH
4
NO
3
.
Recognize that ammonium nitrate is a salt of the
polyatomic ions NH
4
+
and NO
3

.
Recognize that ammonium is a weak acid, and
look up that its K
a
= 5.6x10
10
.
Set up the RICE table and use the K
a
expression.
A) 5.04
B) 4.05
C) 6.50
D) 2.09
E) 5.60
2
Solution
pH = log[H
3
O
+
] = 5.04
+
+
4
2
3
3
7
NH +H O
NH +H O
0.15 M
0
1x10 M
x
+x
+x
0.15x
x
x
2
10
a
2
10
6
3
x
K =
5.6x10
.15x
x =(0.15)(5.6x10
)
x=9.2x10
[
]
H O
Check that the assumption
is OK.
x
< 0.15 M/20.
If
not, need to solve the
quadratic equation using
the
magic formula.
Since Ka is smaller than 10
3
expect x to be small is
assume it is negligible
compared to 0.15 M.
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