9. Calculate the pH of a 0.050M solution of the weak base pyridine (
C
5
H
5
N
) if it has
K
b
= 1.7
x
10
-4
.
Balanced equation:
C
5
H
5
N (aq) + H
2
O (l)
HC
5
H
5
N
+
(aq) + OH
-
(aq)
I.C.E. table:
C
5
H
5
N (aq)
HC
5
H
5
N
+
(aq)
OH
-
(aq)
CHANGE
-xM
+xM
+xM
EQUILIBRIUM
(0.050-x)M
xM
xM
K
b
= 1.7 x
10
-4
= {x
2
} / {(0.050-x)}
What is a valid assumption about x?
a)
x
>> 1.7 x
10
-4
b)
x
>> (0.050-
x
)
c)
x
<< 1.7 x
10
-4
d)
x
<< 0.050
