3. Three components are
involved in the carbonic acid
formation:
CO2(aq)
H2CO3
HCO3
-
true carbonic acid
dissolved CO2
hydrogen carbonate
4. Two of them are bundled
into one entity:
CO2(aq)H2CO3
true carbonic acid dissolved CO2
the composite carbonic acid H2CO3* =
+
It‘s just the composite carbonic acid (and not the
true carbonic acid) that is commonly known as
the carbonic acid.
5. True and Composite Carbonic Acid
true carbonic acid: H2CO3
composite carbonic acid: H2CO3* = CO2(aq) + H2CO3
There are two types of carbonic acid:
Each of these two acids is characterized by
its own equilibrium constant :
Carbonic acid Reaction formula
Equilibrium
constant
true H2CO3 H+ + HCO3
- Ktrue
composite
(apparent)
H2CO3
* H+ + HCO3
- K1
Note:Thisisnot
areactionequation.
6. True and Composite Carbonic Acid
true carbonic acid: H2CO3
composite carbonic acid: H2CO3* = CO2(aq) + H2CO3
There are two types of carbonic acid:
Each of these two acids is characterized by
its own equilibrium constant :
Carbonic acid Reaction formula
Equilibrium
constant
true H2CO3 H+ + HCO3
- Ktrue = 2.0·10-4 M
composite
(apparent)
H2CO3
* H+ + HCO3
- K1 = 4.4·10-7 M
500 times
stronger !
9. Three components are
involved in the carbonic acid
formation:
CO2(aq)
H2CO3
HCO3
-
true carbonic acid
dissolved CO2
hydrogen carbonate
ReactionKinetics
18. Composite Equilibrium Constant K1
The two species CO2(aq) and H2CO3 are treated
together as if they were one substance
(denoted by H2CO3*) with
}COH{}OH)aq(CO{
}HCO}{H{
K
3222
3
1
}COH{
}HCO}{H{
K *
32
3
1