Which term describes an acid that donates a proton?

The term that describes an acid that donates a proton is a Bronsted-Lowry acid. According to the Bronsted-Lowry theory, acids are defined by their ability to donate protons (H⁺ ions), while bases are defined by their ability to accept protons. This framework allows for a broader understanding of acid-base reactions beyond just aqueous solutions, encompassing reactions that occur in different environments.

For instance, if we consider hydrochloric acid (HCl) in aqueous solution, it donates a proton to water, forming hydronium ions (H₃O⁺). This demonstrates the core concept of a Bronsted-Lowry acid, as HCl loses a proton in the process.

In contrast, Lewis acids are defined by their ability to accept electron pairs, which is a different concept, while Arrhenius acids are restricted to substances that increase the concentration of H⁺ ions in an aqueous solution. Conjugate acids are the species formed after a Bronsted-Lowry base accepts a proton; they are not the acids that donate protons themselves but rather the resulting species after the donation has occurred.