The pKa of hydrochloride salt of amphetamine is equal to 9.9.
(1) The major species present in blood, buffered at pH = 7.4, is amphetamine.
(2) The major species present in blood, buffered at pH = 7.4, is amphetamine hydrochloride.
(3) Amphetamine hydrochloride is behaving as an acid in the above equation.