Advanced Placement (AP) Chemistry Practice Exam

Which of the following describes Brønsted-Lowry bases?

1. They produce hydroxide ions in solution

2. They accept protons

3. They donate protons

4. They do not participate in acid-base reactions

The correct answer is: They accept protons

Brønsted-Lowry bases are defined as substances that accept protons (H⁺ ions) in a chemical reaction. This definition is rooted in the concept that acid-base reactions involve the transfer of protons. When a Brønsted-Lowry base encounters a proton donor (an acid), it will accept the proton, thereby forming the conjugate acid of that base. For example, when ammonia (NH₃) acts as a Brønsted-Lowry base, it accepts a proton from water (H₂O), resulting in the formation of ammonium ion (NH₄⁺) and hydroxide ion (OH⁻). This behavior illustrates the fundamental characteristic of Brønsted-Lowry bases. In contrast, the other options do not accurately reflect the definition of Brønsted-Lowry bases. Producing hydroxide ions pertains more to the Arrhenius definition of bases rather than the Brønsted-Lowry framework. Donating protons describes the behavior of Brønsted-Lowry acids, not bases. Lastly, stating that they do not participate in acid-base reactions contradicts their fundamental role in these types of reactions.