A Level Chemistry OCR Practice Exam

What defines an acid in terms of proton transfer?

1. A species that is a proton donor

2. A species that accepts protons

3. A species that neutralizes bases

4. A species that forms hydroxide ions

The correct answer is: A species that is a proton donor

The correct definition of an acid in terms of proton transfer is a species that is a proton donor. In the Brønsted-Lowry theory of acids and bases, an acid is specifically characterized by its ability to donate hydrogen ions (H⁺) to another substance. When an acid dissolves in a solution, it releases protons, leading to an increase in the concentration of hydrogen ions in that solution. This fundamental property differentiates acids from bases, which are defined as proton acceptors. The ability to donate protons is central to understanding acid-base reactions, where the exchange of protons between reactants drives the chemistry involved.