Thanks for your earlier thoughts. Am still working on the problem and would like to know if you have any thoughts on my approach below:

Question

If I have a set of data that gives the apparent partition coefficient as a function of pH, over a range of pH 2-10, how do I calculate the Ka of the compound?

Dr. Bob222, my thought from what I've read:
myweb.brooklyn.liu.edu/msavva/intropartition.pdf

was to use the following relationship for a weak base:

(1/K') = (1/(K*Ka))*[H+] + 1/K

and graph 1/K' vs pH to get the slope and y-intercept which I could then use to determine the Ka. However, when I graph over the entire pH range, I don't get a linear relationship. Since this is a weak base, do you think I should only be graphing out the data from say pH 7-10, or somewhere around this range (5-10, 6-10, etc), as I do get a linear relationship when I ignore the lower pH values. The issue I have though is I'm not sure what pH I should start at, as when I graph out values for pH 5-10 or 6-10 or 7-10, the values that I get for Ka and K are dramatically different for each range. Thanks for any additional insight you might have.

Answer 1

I found this. It may or may not help but further down the page it talks about log D in terms of pH, Ka, etc.
http://en.wikipedia.org/wiki/Partition_coefficient
Sorry I can't be of more help.