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Ch.18 - Aqueous Ionic Equilibrium
Tro - Chemistry: A Molecular Approach 5th Edition
Tro5th EditionChemistry: A Molecular ApproachISBN: 9780134874371Not the one you use?Change textbook
All textbooksTro 5th EditionCh.18 - Aqueous Ionic EquilibriumProblem 58
Chapter 18, Problem 58

Which buffer system is the best choice to create a buffer with pH = 9.00? For the best system, calculate the ratio of the masses of the buffer components required to make the buffer. HF/KF HNO2/KNO2 NH3/NH4Cl HClO/KClO

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1
Step 1: Identify the buffer systems and their corresponding weak acid or weak base and conjugate base or conjugate acid.
Step 2: Use the Henderson-Hasselbalch equation, which is pH = pKa + log([A-]/[HA]), to determine which buffer system has a pKa closest to the desired pH of 9.00.
Step 3: Calculate the pKa for each buffer system using the known Ka values or tables.
Step 4: Once the best buffer system is identified, use the Henderson-Hasselbalch equation to solve for the ratio [A-]/[HA] that gives a pH of 9.00.
Step 5: Convert the ratio of concentrations [A-]/[HA] to the ratio of masses using the molar masses of the buffer components.

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Key Concepts

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

Buffer Systems

A buffer system is a solution that resists changes in pH upon the addition of small amounts of acid or base. It typically consists of a weak acid and its conjugate base or a weak base and its conjugate acid. The effectiveness of a buffer is determined by its pKa and the concentrations of its components, which help maintain a stable pH in a specific range.
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Buffer Capacity

Henderson-Hasselbalch Equation

The Henderson-Hasselbalch equation relates the pH of a buffer solution to the pKa of the acid and the ratio of the concentrations of the conjugate base to the weak acid. It is expressed as pH = pKa + log([A-]/[HA]). This equation is essential for calculating the required ratio of buffer components to achieve a desired pH, such as 9.00 in this case.
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pKa and pH Relationship

The pKa is the negative logarithm of the acid dissociation constant (Ka) and indicates the strength of an acid in solution. A lower pKa value corresponds to a stronger acid. For effective buffering, the pH of the solution should be close to the pKa of the weak acid used in the buffer system, allowing for optimal resistance to pH changes.
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Related Practice
Textbook Question

Blood is buffered by carbonic acid and the bicarbonate ion. Normal blood plasma is 0.024 M in HCO3- and 0.0012 M H2CO3 (pKa1 for H2CO3 at body temperature is 6.1).

c. Given the volume from part (b), what mass of NaOH can be neutralized before the pH rises above 7.8?

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Textbook Question

The fluids within cells are buffered by H2PO4- and HPO42- . b. Could a buffer system employing H3PO4 as the weak acid and H2PO4- as the weak base be used as a buffer system within cells? Explain.

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Textbook Question

A 500.0-mL buffer solution is 0.100 M in HNO2 and 0.150 M in KNO2. Determine if each addition would exceed the capacity of the buffer to neutralize it. a. 250 mg NaOH

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Textbook Question

A 500.0-mL buffer solution is 0.100 M in HNO2 and 0.150 M in KNO2. Determine if each addition would exceed the capacity of the buffer to neutralize it. b. 350 mg KOH

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Textbook Question

A 500.0-mL buffer solution is 0.100 M in HNO2 and 0.150 M in KNO2. Determine if each addition would exceed the capacity of the buffer to neutralize it. c. 1.25 g HBr

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