Final answer:
When an amphoteric molecule is paired with another amphoteric molecule, it can function as either an acid or a base, depending on the nature of the reaction and the species involved.
Step-by-step explanation:
An amphoteric molecule is one that can act as either an acid or a base, depending on its chemical environment. For example, water (H₂O) is an amphoteric substance and, thus, has the ability to either donate a proton (acting as an acid) or accept a proton (acting as a base). When paired with another amphoteric molecule, the result can be one molecule acting as an acid and the other as a base.
This is because these molecules have the ability to react to the presence of stronger acids or bases by donating or accepting protons in order to maintain chemical equilibrium. Therefore, when an amphoteric molecule is paired with another amphoteric molecule, it can act as an acid, a base, or both, depending on the particular reaction. It would not, however, act as neither since their inherent property is to participate in proton transfer reactions.
Take, for instance, the bicarbonate ion (HCO₃⁻), which can either donate a proton to become carbonate (CO₃²⁻), or accept a proton to form carbonic acid (H₂CO₃), showcasing its ability to function in both capacities depending on the surrounding chemical species.