calculate the PH of
0.25M solution of CH3COONa
Answers
Answer:
Sodium acetate is the salt of a weak acid and strong base from the equation:
C
2
H
3
N
a
O
2
→
C
H
3
C
O
O
−
+
N
a
+
, where:
C
H
3
C
O
O
−
+
H
2
O
\
⇌
C
H
3
C
O
O
H
+
O
H
−
As it is a weak acid and strong base, this is a good indicator of a fairly high pH.
K
b
=
[
H
B
+
]
[
O
H
−
]
[
B
]
where:
[
B
]
is the concentration of the base
[
H
B
+
]
is the concentration of base ions.
[
O
H
−
]
is the concentration of the hydroxide ions.
Also,
K
a
K
b
=
1
⋅
10
−
14
/ So,
K
b
=
1
⋅
10
−
14
1.8
⋅
10
−
5
=
5.555
...
⋅
10
−
10
⎡
⎢
⎢
⎢
⎢
⎣
C
H
3
C
O
O
−
C
H
3
C
O
O
H
O
H
−
I
0.150
0
0
C
−
x
+
x
+
x
E
0.150
−
x
x
x
⎤
⎥
⎥
⎥
⎥
⎦
K
b
=
5.555
...
⋅
10
−
10
=
x
2
0.150
−
x
Since the value for
K
b
is small, we will assume the the value for
x
is small, and so will take
0.150
.
So,
x
=
√
0.150
(
5.555
...
⋅
10
−
10
)
=
O
H
−
p
H
=
14
−
p
O
H
=
14
−
(
−
log
(
O
H
−
)
)
=
14
−
(
−
log
(
√
0.150
(
5.555
...
⋅
10
−
10
)
)
)
=
14
−
(
−
log
(
9.128709292
⋅
10
−
6
)
)
=
14
−
5.039590623
≈
8.96