Textbook Question
The acid–base indicator bromcresol green is a weak acid. The yellow acid and blue base forms of the indicator are present in equal concentrations in a solution when the pH is 4.68. What is the pKa for bromcresol green?
Ch.17 - Additional Aspects of Aqueous Equilibria
Chapter 17, Problem 88b
Two buffers are prepared by adding an equal number of moles of formic acid (HCOOH) and sodium formate (HCOONa) to enough water to make 1.00 L of solution. Buffer A is prepared using 1.00 mol each of formic acid and sodium formate. Buffer B is prepared by using 0.010 mol of each. (b) Which buffer will have the greater buffer capacity?
Verified step by step guidance1
Understand the concept of buffer capacity: Buffer capacity is the ability of a buffer solution to resist changes in pH upon the addition of an acid or a base. It is generally proportional to the concentration of the acid and its conjugate base in the buffer.
Identify the components of the buffers: Both Buffer A and Buffer B are composed of formic acid (HCOOH) and its conjugate base, sodium formate (HCOONa).
Compare the concentrations of the buffers: Buffer A has 1.00 mol of each component in 1.00 L of solution, resulting in a concentration of 1.00 M for both the acid and the base. Buffer B has 0.010 mol of each component in 1.00 L of solution, resulting in a concentration of 0.010 M for both the acid and the base.
Relate concentration to buffer capacity: Since buffer capacity is directly related to the concentration of the buffering components, the buffer with the higher concentration of acid and base will have a greater buffer capacity.
Conclude which buffer has greater capacity: Based on the concentrations, Buffer A, with 1.00 M concentrations of both components, will have a greater buffer capacity than Buffer B, which has 0.010 M concentrations.
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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 an 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 results in a greater capacity to neutralize added acids or bases, thus maintaining a stable pH.
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Buffer Capacity
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 pH of the solution and the ratio of the concentrations of the acid and its conjugate base.
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Concentration of Buffer Components
The concentration of buffer components, specifically the weak acid and its conjugate base, directly influences the buffer's effectiveness. In this scenario, Buffer A has a higher concentration (1.00 mol each) compared to Buffer B (0.010 mol each). Higher concentrations lead to increased interactions with added acids or bases, enhancing the buffer's ability to maintain pH stability.
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Related Practice
Textbook Question
A sample of 0.2140 g of an unknown monoprotic acid was dissolved in 25.0 mL of water and titrated with 0.0950 M NaOH. The acid required 30.0 mL of base to reach the equivalence point. (a) What is the molar mass of the acid?
Textbook Question
A sample of 0.1687 g of an unknown monoprotic acid was dissolved in 25.0 mL of water and titrated with 0.1150 M NaOH. The acid required 15.5 mL of base to reach the equivalence point. (a) What is the molar mass of the acid?