For any acid/base,
HA <----> H+ + A-
K = [H+][A-]/[HA]
Thus,
pK = pH - log{[A-]/[HA]}
--> pH = pK + log{[A-]/[HA]}
* i.e. Henderson-Hasselbalch equation
NB:
--> pH = pK + log{[A-]/[HA]}
(See above)
CO2 + H2O
<---> H2CO3
<---> H+ + HCO3-
pH = pK + log {[HCO3-]/[H2CO3]}
When [H2CO3] is changed to [CO2]
--> pK becomes pK' to denote two related but different values
Also,
pKa varies with temperature
--> pKa = 6.1 at 37C
Thus,
pH = 6.1 + log {[HCO3-]/[CO2]}
Also,
CO2 solubility = 0.0301 mmol/L/mmHg of pCO2
Thus,
pH = 6.1 + log {[HCO3-]/(0.0301 x pCO2)}
NB: