Textbook Question
The pH of a solution of NH3 and NH4Br is 8.90. What is the molarity of NH4Br if the molarity of NH3 is 0.016 M?
Ch.17 - Applications of Aqueous Equilibria
Chapter 17, Problem 64
Which of the following gives a buffer solution when equal volumes of the two solutions are mixed?(a) 0.10 M NH3 and 0.10 M HCl(b) 0.20 M NH3 and 0.10 M HCl(c) 0.10 M NH4Cl and 0.10 M NH3 (d) 0.20 M NH4Cl and 0.10 M NaOH
Verified step by step guidance1
Step 1: Understand what a buffer solution is. A buffer solution is a solution that can resist changes in pH when small amounts of an acid or a base are added. It is usually made up of a weak acid and its conjugate base, or a weak base and its conjugate acid.
Step 2: Identify the weak base and its conjugate acid in the given options. In this case, NH3 is a weak base and its conjugate acid is NH4+ (which is present in NH4Cl).
Step 3: Look for the option where both the weak base (NH3) and its conjugate acid (NH4+) are present. This is because a buffer solution is formed when a weak base and its conjugate acid (or a weak acid and its conjugate base) are mixed together.
Step 4: From the given options, (c) 0.10 M NH4Cl and 0.10 M NH3 is the pair that forms a buffer solution. This is because NH4Cl is a source of NH4+ (the conjugate acid of NH3) and NH3 is the weak base.
Step 5: Note that the other options do not form a buffer solution because they do not contain both a weak base and its conjugate acid. For example, in option (a), HCl is a strong acid, not a weak one, so it does not form a buffer with NH3. Similarly, in option (d), NaOH is a strong base, not a weak one, so it does not form a buffer with NH4Cl.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Buffer Solutions
A buffer solution is a system 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. This equilibrium allows the buffer to neutralize added acids or bases, maintaining a relatively stable pH.
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Buffer Solutions
Weak Acids and Bases
Weak acids and bases are substances that do not completely dissociate in solution. For example, ammonia (NH3) is a weak base that partially reacts with water to form ammonium ions (NH4+) and hydroxide ions (OH-). Understanding the behavior of weak acids and bases is crucial for predicting how they will interact in buffer solutions.
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Conjugate Acid-Base Pairs
Conjugate acid-base pairs consist of an acid and a base that differ by a single proton (H+). For instance, NH3 (base) and NH4+ (conjugate acid) form a pair. The presence of both components in a solution is essential for creating a buffer, as they can react with added acids or bases to minimize pH changes.
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Related Practice
Textbook Question
Which of the following solutions has the greater buffer capacity: 100 mL of 0.30 M HNO2-0.30 M NaNO2 or 100 mL of 0.10 M HNO2-0.10 M NaNO2? Explain.
Textbook Question
Calculate the pH of a buffer solution that is 0.20 M in HCN and 0.12 M in NaCN. Will the pH change if the solution is diluted by a factor of 2? Explain.