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

Determine whether or not the mixing of each pair of solutions results in a buffer. c. 225.0 mL of 0.10 M NH3 ; 250.0 mL of 0.15 M NH4Cl

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Identify the components of the solutions: NH3 is a weak base and NH4Cl is its conjugate acid.
Calculate the moles of NH3 using the formula: moles = concentration (M) x volume (L).
Calculate the moles of NH4Cl using the formula: moles = concentration (M) x volume (L).
Determine if the solution can act as a buffer by checking if both the weak base (NH3) and its conjugate acid (NH4+) are present in significant amounts.
Conclude that the mixture forms a buffer if both components are present in comparable amounts, allowing the solution to resist changes in pH.

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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. In this case, the combination of ammonia (NH3) and ammonium chloride (NH4Cl) can create a buffer because NH3 is a weak base and NH4Cl provides the conjugate acid (NH4+).
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Buffer Solutions

Weak Bases and Conjugate Acids

Weak bases are substances that partially dissociate in solution to produce hydroxide ions (OH-). Ammonia (NH3) is a common weak base. When it is mixed with a salt like ammonium chloride (NH4Cl), which dissociates to provide NH4+, the resulting solution can maintain a relatively stable pH, characteristic of buffer solutions.
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Henderson-Hasselbalch Equation

The Henderson-Hasselbalch equation is a mathematical formula used to calculate the pH of a buffer solution. It relates the pH to the pKa of the weak acid and the ratio of the concentrations of the conjugate base and the weak acid. For the NH3/NH4Cl system, this equation can help determine the effectiveness of the buffer in maintaining pH when acids or bases are added.
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