Aqueous CO2 Chemistry

1
Aqueous CO2 Chemistry
CO2(aq) PCO2
CO2 is soluble in water CO2(g) ? CO2(aq)
K ------------ 0.034
(atmospheres)
H2CO3 CO2(aq)
K ------------ 1.3 x 10-3
CO2 reacts with water CO2(aq) H2O ? H2CO3
weak acid, Ka 2 x 10-4
often, the Ka of H2CO3 is reported as 4.4 x
10-7, which assumes that all dissolved CO2 is in
the form carbonic acid
HCO3-H H2CO3
Ka --------------------- 2 x 10-4
H2CO3 HCO3- H
If atmospheric CO2 concentration is 370 ppm, what
is the expected pH of rain?
2
Aqueous CO2 Chemistry
If atmospheric CO2 concentration is 370 ppm, what
is the expected pH of rain?
CO2(aq) PCO2
CO2(aq) 0.034 x (370/106) 12 ?M
K ------------ 0.034
(atmospheres)
by convention, CO2(aq) H2CO3 and K1, K2
reported as 4.45x10-7, 4.84x10-11, respectively
H2CO3 CO2(aq)
K ------------ 1.3 x 10-3
H2CO3 (1.3 x 10-3) x (1.2 x 10-5 M) 1.56 x
10-8 M
HCO3-H H2CO3
H v(2 x 10-4) x (1.56 x 10-8) 1.77 x
10-6 M
Ka --------------------- 2 x 10-4
pH -logH -log(1.77 x 10-6) 5.75 natural
rain water is acidic due to atmospheric CO2