pKa values are constants. Good collections of such data can be found here: http://evans.rc.fas.harvard.edu/pdf/evans_pKa_table.pdf

or here: http://www.chem.wisc.edu/areas/reich/pkatable/pKa_compilation-1-Williams.pdf

Thank you so much for the articles that you give to me. I hope that articles will very helpful for my paper

Dear Buti Ayunda you can take healp from this article.