Which of the following solutions has the greater buffer capacity: 50 mL of 0.20 M NH4Br-0.30 M NH3 or 50 mL of 0.40 M NH4Br-0.60 M NH3? Explain.

Name: Chemistry
Author: McMurry
ISBN: 9781292336145

Verified step by step guidance

Identify the components of the buffer solution: NH4Br provides NH4+ ions, and NH3 is the weak base.

Understand that buffer capacity is the ability of a buffer to resist changes in pH upon the addition of an acid or base, and it is generally higher when the concentrations of the buffer components are higher.

Compare the concentrations of NH4+ and NH3 in both solutions. The first solution has 0.20 M NH4+ and 0.30 M NH3, while the second solution has 0.40 M NH4+ and 0.60 M NH3.

Recognize that the buffer capacity is directly proportional to the concentrations of the acid and base components. Therefore, higher concentrations of NH4+ and NH3 will result in a greater buffer capacity.

Conclude that the second solution, with 0.40 M NH4+ and 0.60 M NH3, has a greater buffer capacity than the first solution.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Buffer Capacity

Buffer capacity refers to the ability of a buffer solution to resist changes in pH upon the addition of small amounts of acid or base. It is determined by the concentrations of the weak acid and its conjugate base present in the solution. A higher concentration of these components generally leads to a greater buffer capacity, allowing the solution to maintain its pH more effectively.

Henderson-Hasselbalch Equation

The Henderson-Hasselbalch equation is a mathematical formula used to calculate the pH of a buffer solution. It is expressed as pH = pKa + log([A-]/[HA]), where [A-] is the concentration of the conjugate base and [HA] is the concentration of the weak acid. This equation highlights the relationship between the concentrations of the buffer components and the resulting pH, which is crucial for understanding buffer effectiveness.

Concentration of Buffer Components

The concentration of buffer components, specifically the weak acid and its conjugate base, directly influences the buffer's capacity. In the given question, comparing the concentrations of NH4Br (the weak acid) and NH3 (the conjugate base) in each solution allows us to determine which buffer can better resist pH changes. Higher concentrations of these components lead to a more effective buffer system.