A. At what pH are about 1/2 of the carboxyl groups ionized? pH = B. Where does the amino acid have a net charge of +1? below pH 2.34 at pH = 2.34 at pH = 6.01 at pH = 9.69 above pH 9.69 C. At what point has enough base been added to react with 1/2 of the COOH groups? 1/2 of COOH reacted = equivalents OH− when 1/2 of COOH has reacted, the pH = D. At which pH value does the amino acid have the best buffering capacity? 1.53 10.5 2.34 6.01 3.00 9.00 E. What is the pI (isoelectric point)? pI =