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Ch.18 - Aqueous Ionic Equilibrium
Chapter 18, Problem 56b

Determine whether or not the mixing of each pair of solutions results in a buffer. b.155.0 mL of 0.15 M NH3 ; 155.0 mL of 0.10 M HCl

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1
Identify the components needed for a buffer solution: a weak base and its conjugate acid, or a weak acid and its conjugate base.
Recognize that NH3 (ammonia) is a weak base and HCl (hydrochloric acid) is a strong acid.
Calculate the moles of NH3 using the formula: moles = concentration (M) \times volume (L).
Calculate the moles of HCl using the formula: moles = concentration (M) \times volume (L).
Determine if the amount of HCl is enough to partially neutralize NH3, forming NH4^+ (the conjugate acid), without completely neutralizing it, which would result in a buffer solution.

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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. Buffers are crucial in maintaining stable pH levels in various chemical and biological processes.
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Buffer Solutions

Weak Bases and Their Conjugate Acids

Weak bases, like ammonia (NH3), partially ionize in solution to form hydroxide ions (OH-) and their conjugate acids. When mixed with a strong acid, such as hydrochloric acid (HCl), the weak base can react with the acid to form its conjugate acid, which is essential for buffer formation. Understanding this equilibrium is key to determining buffer capacity.
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Conjugate Acid-Base Relationships

pH and Acid-Base Reactions

pH is a measure of the acidity or basicity of a solution, defined as the negative logarithm of the hydrogen ion concentration. In acid-base reactions, the pH changes based on the concentrations of acids and bases present. Analyzing the resulting pH after mixing solutions helps determine if a buffer is formed, as buffers maintain a relatively constant pH.
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