Calculate apparent pKa for a mixture of two compounds?

Hi all,

 

I am looking for a way to calculate an apparent pKa for a mixture of two compounds.  I can calculate the microspecies pKas of each compound separately, but am looking for a global apparent pKa when the two compounds are mixed together in solution.  

 

Does anyone know of a way to do this using the ChemAxon software packages?

 

Thanks a lot,

Daniel

Hi,

 

You can try to calculate  the apparent pKa for a simple case.   I attached an Excel file. You can change the "pKa1" , "pKa2" and the "raito" of the "2nd" and the "1st" molecules. The "apparent pKa" is the "-" interception value  of the fitted line (see in the right bottom corner in the orange box).

 

eg. pKa1= 6 , pKa2=4 and ratio = 1/2,   ==> pKa,apparent = 4.4653

 

Jozsi

Thanks!