how to obtain CCL3COOH
Answers
Explanation:
Answer
anor277
Apr 7, 2016
With difficulty, inasmuch you neglected to include the acid dissociation constant,
K
a
, of
C
l
3
C
(
=
O
)
O
H
. I got
p
H
=
0.804
Explanation:
From this site I learn that
K
a
,
C
l
3
C
(
=
O
)
O
H
=
2.2
×
10
−
1
.
This is fairly large as an organic acid, and likely the method of successive approximations will be inadequate:
C
l
3
C
(
=
O
)
O
H
+
H
2
O
⇌
C
l
3
C
(
=
O
)
O
−
+
H
3
O
+
So
K
a
=
2.2
×
10
−
1
=
[
H
3
O
+
]
[
C
l
3
C
(
=
O
)
O
−
]
[
C
l
3
C
(
=
O
)
O
H
]
If I put
[
H
3
O
+
]
=
x
, then
K
a
=
2.2
×
10
−
1
=
x
2
0.268
−
x
Solving this quadratic equation, I get two solutions:
x
1
=
0.157
;
x
2
=
−
0.377
. I had to use the quadratic equation to get this answer.
Clearly,
x
1
=
0.157
is the required answer.
Thus
[
H
3
O
+
]
=
0.157
m
o
l
⋅
L
−
1
=
[
C
l
3
C
(
=
O
)
O
−
]
AND
[
C
l
3
C
(
=
O
)
O
H
]
=
(
0.268
−
0.157
)
⋅
m
o
l
⋅
L
−
1
=
0.111
⋅
m
o
l
⋅
L
−
1
.
Thus
p
H
=
−
log
10
{
0.157
}
=
0.804
Please check the validity of this calculation. I am still using a web based calculator because my calculator (which has this programmed) has gone walkabout. Note that the
p
H
of this solution is low because trichloroacetic acid is strongish, certainly stronger than acetic acid. As far as I know this is an entropy rather than a enthalpy phenomenon. Trichloroacetate is a much less polarizing ion than acetate, and is entropically favoured.