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Ch.17 - Aqueous Ionic Equilibrium
Chapter 17, Problem 53e

Determine whether or not the mixing of each pair of solutions results in a buffer. e. 125.0 mL of 0.15 M NH3; 150.0 mL of 0.20 M NaOH

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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 NaOH (sodium hydroxide) is a strong base.
Calculate the moles of NH3 using the formula: moles = concentration (M) \times volume (L).
Calculate the moles of NaOH using the formula: moles = concentration (M) \times volume (L).
Determine if the strong base (NaOH) will convert some of the weak base (NH3) into its conjugate acid (NH4+), and check if there is enough NH3 left to form a buffer.

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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 maintain pH stability, which is crucial in many chemical and biological processes.
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Buffer Solutions

Weak Bases and Conjugate Acids

Weak bases, like ammonia (NH3), partially ionize in solution to form hydroxide ions (OH-) and their conjugate acids. The presence of both the weak base and its conjugate acid in a solution is essential for buffer action. In this case, NH3 can act as a weak base, while NH4+ (ammonium ion) would be its conjugate acid.
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pH and Hydroxide Ion Concentration

The pH of a solution is a measure of its acidity or basicity, determined by the concentration of hydrogen ions (H+). When mixing solutions, the resulting pH depends on the concentrations of acids and bases present. In this scenario, the addition of NaOH, a strong base, will affect the overall pH and the potential for buffer formation with NH3.
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Hydroxide Ion Concentration Example