Can pH be calculated from raw chemistry composition alone?

[tring]

I need to know whether, given the actual composition of a synthetic fluid (in water) stated as concentrations of Na, K, Cl, urea, NH4, phosphate, citrate, and creatinine a resulting pH can be computed from first principles given the involved pKs - 3 for phosphate and citrate, one for creatinine and one for NH4. I ask because I (think) I can and just wanted to make sure that everybody else already knew how to do it. I do not need to have concentration of conjugate acid and base - just the raw total concentration. Is that well known?

 

[Borek]

In general - yes. But you may hit a wall if ionic strength of the solution is too high.

 

[tring]

Thanks a lot. I saw your page
http://www.chembuddy.com/?left=pH-calculation&right=general-pH-calculation
that you method is exactly what I have used: writing up all equations and mass balances under charge balance. Only I do not need any simplifications.
Thanks a lot

 

[Borek]

Simplifications make sense when you want to do calculatoins by hand, in this case you will most likely need full set of equations, that requires numerical approach, that in turn means - no simplifications needed.

 

[tring]

Thanks again. You may be surprised but this fact is seemingly unknown to many in renal physiology, and at least it is unused. Might you have a single reference on the subject? With regard to the ionic strenght question, is the problem that the pks become difficult to know or is it something else?

 

[Borek]

Start with my page here:

ionic strength activity coefficients

I suppose more can be found on the web, but honestly - I never needed that. There is a detailed description of the problem in Electrochemistry by Koryta, Dvorak and Bohackova (that's what I have at home, doesn't mean that's the only reliable source).

 

[GCT]

I need to know whether, given the actual composition of a synthetic fluid (in water) stated as concentrations of Na, K, Cl, urea, NH4, phosphate, citrate, and creatinine a resulting pH can be computed from first principles given the involved pKs - 3 for phosphate and citrate, one for creatinine and one for NH4. I ask because I (think) I can and just wanted to make sure that everybody else already knew how to do it. I do not need to have concentration of conjugate acid and base - just the raw total concentration. Is that well known?

You need this

http://www.chem1.com/acad/pdf/envacid.pdf

Also is that Creatine Phosphate - as in the covalent compound - and perhaps ammonium citrate?

 

[tring]

Thanks a lot for the pdf. I found it very supporting of the view that given the "raw" chemistry, pH should be defined by that alone. Another matter is actually to calculate it exactly against difficulties in knowing activity coefficients, which influence both the pks and the SID as defined in the pdf referred to.
Best wishes
Troels