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Re: CO2 and O2

Hi Naomi,

I did not managed to find my Chemical Engineering Textbooks but somewhat
got it roughly figured out.  This gonna be long, those who aren't
interested should skip this.

The amount of CO2 you can get into the water depends on the following.

(1)  Solubility of CO2 in water. (In equilibrium with CO2 escaping back to
atmosphere)
     CO2(g)  <---->  CO2(aq)
     Factors affecting: temperature, atmospheric pressure, dissolved
gases(including dissolved O2 & CO2), concentration of CO2 in air contacting
with H20
(Note that surface turbulance only cause the system to reach equilibrium
faster.)

(2)  Dissolved CO2 interacting with water to form carbonic acid.
     CO2(aq)  +  H20  <---->  H+  +  HCO3-
     pH will lower due to this reaction with H20.
     Factors affecting:  Amount of dissolved CO2, KH (concentration of
HCO3- in water), pH (concentration of H+ in water)

(3)  Amount of HCO3- in water
     2CO3--  +  H2O  <---->  0H-  +  HCO3-
     Factors affecting:  KH & PH (interacting directly with (2))

(4)  Consumption of CO2 & HCO3- by plants
     Factors affecting:  no. of plants, light (photosynthesis)

(5)  Respiration of organisms.
     Factors affecting:  population of organisms, metabolism rate


The amount of O2 you can get into the water depends on the following.

(1)  Solubility of O2 in water. (In equilibrium with O2 escaping back to
atmosphere)
     O2(g)  <---->  O2(aq)
     Factors affecting: temperature, atmospheric pressure, dissolved
gases(including dissolved O2 & CO2), concentration of O2 in air contacting
with H20
(Note that surface turbulance only cause the system to reach equilibrium
faster.)

(2)  Releasing of O2 by plants
     Factors affecting:  no. of plants, light (photosynthesis)

(3)  Respiration of organisms.
     Factors affecting:  population of organisms, metabolism rate


All the above are in a dynamic equilibrium(steady state as Tom mentioned).
Due to the fact that most of the dissolved CO2 turns into carbonic acid
(which explains the pH drop when adding CO2), it do not contribute too much
as a factor limiting the solubility of O2.  I think you should be able to
figure out the relationship between dissolving CO2 and O2.  Hope that this
helps.

BC (Singapore)