The dissociation constant (pK) is the pH at which 50% of a compound (functional group) is protonated. Following are some examples of Weak Acid and Weak Base Chemical Functional Groups and their approximate pK’s.

 

Acids pK
 Sulfonic Acid <1
 Phosphate Ester 2
 Carboxylic Acid 2.5-5
 Uracil 8
 Sulfonamide 7-9
 Guanine 2.2, 9.4
 Phenol 8-10

 

 

Bases pK
 Pyridine 5
 Analine 5
 Amine 7-10
 Imidazole 7