Chemistry Regents Practice Test

According to one acid-base theory, what is defined as an acid?

1. H+ ion acceptor

2. H+ donor

3. pH below 7

4. Any corrosive substance

The correct answer is: H+ donor

In the context of acid-base theory, specifically the Brønsted-Lowry theory, an acid is defined as a substance that donates a proton (H+ ion) to another substance. This definition emphasizes the transfer of protons during chemical reactions, which plays a crucial role in the behavior of acids and bases in aqueous solutions. When an acid donates an H+ ion, it increases the concentration of protons in the solution, which is a characteristic behavior of acids. This proton donation leads to a variety of chemical reactions, including those that form conjugate bases and influence pH levels in solutions. Therefore, identifying an acid as an H+ donor aligns well with this theory and highlights the fundamental interaction that occurs in acid-base chemistry. The other definitions provided do not accurately represent the concept of an acid in this context. For instance, while an H+ ion acceptor characterizes a base, a pH below 7 indicates acidity but does not define what makes a substance an acid, and referring to any corrosive substance does not specifically relate to the chemical behavior regarding H+ ion transfer.