One of the questions in my Biochemistry book asks when the side chain of Histidine has been completely titrated. It lists the pKa of the side chain as 6.0 and it gives a titration curve and lists several points on the curve. The answer in the book says that point 5 is when the side chain is completely titrated. What I don't understand is that point 5 is at a pH of about 7.5. Wouldn't the pH have to be above 8 before you could consider the side chain to be completely titrated? Am I misunderstanding what it means for something to be fully titrated?