When is a substance considered amphoteric?

A substance is considered amphoteric when it has the ability to act as both an acid and a base, depending on the surrounding environment or conditions. This dual role means that such a substance can donate a proton (acting as an acid) or accept a proton (acting as a base).

For instance, water is a classic example of an amphoteric substance. In the presence of a strong acid, water can accept a proton and behave as a base. Conversely, in the presence of a strong base, water can donate a proton and function as an acid. The amphoteric nature is essential for maintaining chemical equilibrium in various reactions, particularly in biological systems.

Recognizing this definition allows you to distinguish amphoteric substances from others that are strictly acids or bases. This characteristic is key in understanding acid-base chemistry and the behavior of different compounds in varying chemical environments.