The amino acid glycine (Gly) is often used as the main ingredient of a buffer in biochemical experiments. The amino group of glycine, which has a pKa of 9.6, can exist either in the protonated form...

The amino acid glycine (Gly) is often used as the main ingredient of a buffer in biochemical experiments. The amino group of glycine, which has a pKa of 9.6, can exist either in the protonated form (-NH3⁺) or as the free base (-NH2), because of the reversible equilibrium:

R-NH3⁺<-------> R-NH2 + H⁺

Question : When 75% of the glycine amino groups are in their protonated forms, what is the pH of the solution?