Physician Assistant College Admission Test (PA-CAT) Entrance Practice exam

A Bronsted-Lowry acid is defined as a substance that can donate a proton (H+) to another substance during a chemical reaction. In this context, CH3COOH, or acetic acid, is a classic example because it readily donates a proton to form its conjugate base, CH3COO-.

When acetic acid is dissolved in water, it dissociates slightly, releasing H+ ions into the solution. This behavior demonstrates the key characteristic of a Bronsted-Lowry acid, which is its ability to increase the concentration of hydrogen ions in a solution.

Other substances presented in the choices either do not fit the definition of a Bronsted-Lowry acid or show different chemical behaviors. For instance, NH3 (ammonia) is typically a Bronsted-Lowry base, as it can accept protons rather than donate them. H2O (water) can act as either an acid or a base depending on the context, but in the case of acetic acid, it is the acetic acid that serves as the Bronsted-Lowry acid. NaOH (sodium hydroxide) is a strong base that dissociates to release hydroxide ions (OH-) but does not donate