Consider the stomach @ pH ~ 2 , pH= pKa+log [A-]/[HA],

pKa log [A-]/[HA] [A-]/[HA] % unionized
1 1 10 9.1
2 0 1 50
3 -1 10-1 91
4 -2 10-2 99.1
6 -4 10-4 99.991
8 -6 10-6 99.9991

 

 

 

 

 

 

 

 

 

 

Example: absorption of benzoic acid:

I) Stomach - assume pH=2, pKa =4 for benzoic acid.

 

equilibrium of benzoic acid between stomach and plasma using structural drawings of ionization states of benzoic acid

 

 

 

 

 

 

 

 

 

 

 

 

 

 

thiopental (anesthetic): thiopental structural drawing

 

 

 

 

Last modified 18 February 2010