[Maramaldo]

[Maramaldo]

I mean: I can't just apply Henry's law to a buffer solution, right?

[Arkcon]

Maybe there's a table published somewhere, a media vendor might offer one, that you can look up values in.  You can always try to determine the equilibrium between the 5% CO2 atmosphere, and the bicarbonate in solution, accounting for the phosphate buffering, and the effect of other ions, but it seems to me like the calculation requires to many assumptions on ideal, and this case is too real world to work.

[Maramaldo]

Thank you for your reply! Indeed I couldn't find any table possibily because ringer is generally prepared in the laboratory (with little variations in the composition according to the experimental system used).

I understand what you say about calculations' assumptions, but for me is more important to understand how concentration ratio and pH whill change in principle, rather than having "exact" values that I can trust (for that maybe it would be possible to use a CO2 elctrode).

So this is how I would start to describe the thing:

let's say that I have a partial pressure of 0.05 atm of CO2 and a pure water solution. Then I can express the concentration of CO2 in water by henry's law [CO2]/=PCO2/Kh

and then my system (from wikipedia on carbonic acid):

[H+][OH-]= 10^-14

K0=[H2C03]/[C02]

Ka1=[H+][HCO3-]/[H2C03]

Ka2=[H+][CO3--]/[HC03-]

[H+]=[OH-]+[HCO3-]+2[C03--]

So I can calculate my pH and [HC03-];  but I'm instead using a buffer solution, so how the two factors will vary? I can apply similar equations for the phosphate buffer, but I don't quite understand where to add the concentration of NaHCO3 salt in all that...


I guess that having a 10 equations 10 unknowns system is not really helpful, but maybe it's then possible to simplify the problem..