Advanced Placement (AP) Chemistry Practice Exam

What does the Henderson-Hasselbalch equation describe?

1. The relationship between hydrogen ion concentration and pH.

2. The relationship between pH and the ratio of acid and conjugate base concentrations.

3. The relationship between temperature and reaction rates.

4. The relationship between solubility and pressure.

The correct answer is: The relationship between pH and the ratio of acid and conjugate base concentrations.

The Henderson-Hasselbalch equation specifically describes the relationship between pH and the ratio of the concentrations of an acid and its conjugate base in a solution. It is often expressed as: \[ \text{pH} = \text{pKa} + \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right) \] In this equation, pH is the measure of the acidity of the solution, pKa is the acidity constant of the acid, \([\text{A}^-]\) is the concentration of the conjugate base, and \([\text{HA}]\) is the concentration of the acid. This equation illustrates how changes in the concentrations of the acid and conjugate base will affect the overall pH of the solution, making it a crucial tool in buffer solution calculations and understanding acid-base equilibria. Other options listed pertain to different concepts in chemistry. The relationship between hydrogen ion concentration and pH is indeed relevant, but it is not the primary focus of the Henderson-Hasselbalch equation. The relationship between temperature and reaction rates relates to the collision theory and Arrhenius equation, while solubility and pressure are covered