Explanation:
Ethanoic acid is a weak acid and dissociates:
C
H
3
C
O
O
H
⇌
C
H
3
C
O
O
−
+
H
+
For which
K
a
=
[
C
H
3
C
O
O
−
]
[
H
+
]
[
C
H
3
C
O
O
H
]
=
1.8
×
10
−
5
Please remember that these are equilibrium concentrations .
p
K
a
=
−
log
K
a
=
−
log
[
1.8
×
10
−
5
]
=
4.74
n
=
c
×
v
∴
n
C
H
3
C
O
O
H
=
0.20
×
200.0
1000
=
0.04
