Question

Calculate the concentration of CO32− , H3O+ , and OH− in a 0.155 M M solution of H2CO3 . ( Ka1=4.3×10−7 and Ka2=5.6×10−11 .)

Answer 1

H
2
C
O
3
⇌
H
+
+
H
C
O
3
−




K
a
1
=
4.2
×
10
−
7
H
C
O
3
−
⇌
H
+
+
C
O
3
2
−







K
a
2
=
4.8
×
10
−
11


First, we will use the first dissociation constant to find the concentration of
H
C
O
3
−
.



K
a
1
=
[
H
+
]
[
H
C
O
3
−
]
[
H
2
C
O
3
]
[
H
+
]
=
[
H
C
O
3
−
]
4.2
×
10
−
7
=
[
H
+
]
[
H
+
]
0.035
[
H
+
]
2
=
1.47
×
10
−
8
[
H
+
]
=
1.21
×
10
−
4

M



Now, we will use the second dissociation constant to find the concentration of
C
O
3
2
−
: