QCAA Chemistry Practice Test

Amphiprotic describes a species that can act as both an acid and a base in proton transfer reactions. In Bronsted-Lowry terms, an acid donates a proton and a base accepts one, and an amphiprotic substance is capable of doing either depending on the reacting partner. Water is the classic example: it can donate a proton to form hydroxide (H2O → H+ + OH−) or accept a proton to form hydronium (H2O + H+ → H3O+). This dual capability is what makes amphiprotic the best descriptor. Conjugate base and conjugate acid refer to forms produced after donation or acceptance, respectively, and a Bronsted-Lowry acid describes only the proton-donor role.