31. calculation of pka an unknown compound, x, is thought to have a carboxyl group with a pka of 2.0 and another ionizable group with a pka between 5 and 8. when 75 ml of 0.1 m naoh is added to 100 ml of a 0.1 m solution of x at ph 2.0, the ph increases to 6.72. calculate the pka of the second ionizable group of x.