© A.W.Marczewski 2002

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CO2 in air/water:

Data sources

  1. Solubility of CO2 in water - dependence on temperature
  2. Ionization constants: pKa1 and pKa2 and pKa1=f(T)
  3. Ionization of CO2 in water - composition and pH
  4. Titration of acidified electrolyte with NaOH: effect of CO2-contaminated NaOH and CO2 in electrolyte (equlibrated in contact with air).

R
solubility as CO2 [mol] / [dm3] of pure water
q
solubility as mass of CO2 [g] dissolved in 100g of pure water
a
Bunsen solubility coeff. as CO2 volume [dm3] / [dm3] of pure water
Ionization constants:
(1) relative to total CO2 content (CO2 + H2CO3) at 25C:
pKa1=6.352, pKa2=10.329 (or 10.24 - Ref. dependent)
(2) relative to actual H2CO3 at 25C: pKa1=3.76

Solubility and dissociation of CO2 in water:
Solubility:
Normal curves: R, q, a = f(T)
Solubility:
Linearized log(R) = f(1/T)
pKa1 = f(T)
(relative to total CO2)
solubility of CO2 in water solubility of CO2 in water, linearized - log(R) = f(1/T) pKa1 of CO2 as a function of temperature (relative to total CO2+H2CO3 content)

Composition and pH of CO2 equilibrated water:
NOTE For simplicity, activity coefficients were ignored (usually titration is performed at constant ionic strength - relative pH changes are only weakly affected.
Equilibrium composition = f(pH):
0.03% of CO2 in air at 25C
Zoomed view of
Equilibrium composition = f(pH):
0.03% of CO2 in air at 25C
pH of water equilibrated
against atmospheric CO2 at 25C
(0.03% in air is marked)
Equilibrium composition = f(pH): 0.03% of CO2 in air at 25C (zoomed) Equilibrium composition = f(pH): 0.03% of CO2 in air at 25C pH of water equilibrated against atmospheric CO2 at 25C

Titration of HCl with NaOH:
NOTE For simplicity, activity coefficients were ignored (usually titration is performed at constant ionic strength - relative pH changes are only weakly affected.

Model lines:
30ml of electrolyte solution (e.g. 0.1M NaCl - see NOTE above) is acidified with 0.3ml of 0.2M HCl. Then solution is titrated with 0.1M NaOH at T=298K.

Titration of HCl with NaOH (model):
Full range curve Enlarged range
(close to pH=7)
influence of atmoshperic CO2 and carbonates on titration influence of atmoshperic CO2 and carbonates on titration (enlarged)
Compare general potentiometric titration page.


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