Agriculture Reference
In-Depth Information
Table 3.3
Equilibria in aqueous carbonate solutions
Species
CO
2
(
g
),
CO
2
(
aq
),
H
2
CO
3
,
HCO
3
−
,
CO
3
2
−
,
H
+
,
OH
−
,
M
+
,
X
−
[H
2
CO
3
∗
]
a
=
[CO
2
(
aq
)
]
+
[H
2
CO
3
]
Equilibria
b
[CO
2
(
aq
)
]
/
[CO
2
(
g
)
]
=
H
c
(0)
[H
2
CO
3
∗
]
/p
CO2
=
K
H
(0a)
[CO
2
(
aq
)
]
/
[H
2
CO
3
]
=
K
(1)
[H
+
][HCO
3
−
]
/
[H
2
CO
3
]
=
K
H
2
CO
3
(2)
[H
+
][HCO
3
−
]
/
[H
2
CO
3
∗
]
=
K
1
(2a)
[H
+
][CO
3
2
−
]
/
[HCO
3
−
]
=
K
2
(3)
[H
+
][OH
−
]
=
K
W
(4)
Ionization fractions for constant total carbonate concentration,
C
T
C
T
=
[H
2
CO
3
∗
]
+
[HCO
3
−
]
+
[CO
3
2
−
]
(5)
[H
2
CO
3
∗
]
=
α
0
C
T
[HCO
3
−
]
=
α
1
C
T
[CO
3
2
−
]
=
α
2
C
T
1
+
[H
+
]
2
−
1
K
1
[H
+
]
+
K
1
K
2
α
0
=
(6)
[H
+
]
K
1
−
1
K
2
[H
+
]
α
1
=
+
1
+
(7)
[H
+
]
2
K
1
K
2
+
1
−
1
[H
+
]
K
2
α
2
=
+
(8)
Electrical neutrality condition
[H
+
]
+
[M
+
]
=
[HCO
3
−
]
+
2[CO
3
2
−
]
+
[OH
−
]
+
[X
−
]
(9)
a
The 'apparent' concentration of H
2
CO
3
since [CO
2
(
aq
)
]
[H
2
CO
3
].
b
Equilibrium constants are defined at constant ionic strength.
c
Dimensionless Henry's law constant, in which [CO
2
(
g
)
]
P
CO
2
/RT
.
Source
: Stumm and Morgan (1996). Reproduced by permission of Wiley, New York.
=
Table 3.4
Equilibrium constants for carbonate equilib-
ria at 25
◦
C
,I
=
0
Equilibrium
Constant
−
log
K
H
2
CO
3
∗
K
H
a
CO
2
(
g
)
+
H
2
O
=
3.47
H
2
CO
3
∗
=
H
+
+
HCO
3
−
K
1
6.35
HCO
3
−
=
H
+
+
CO
3
2
−
K
2
10.33
H
+
+
OH
−
H
2
O
=
K
W
14.0
a
P
CO
2
in kPa.
