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Ch.16 - Acids and Bases
Chapter 16, Problem 89

Determine the [OH], pH, and pOH of a 0.15 M ammonia solution.

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Key Concepts

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

Ammonia as a Weak Base

Ammonia (NH3) is a weak base that partially ionizes in water to form hydroxide ions (OH-) and ammonium ions (NH4+). The equilibrium reaction can be represented as NH3 + H2O ⇌ NH4+ + OH-. Understanding this equilibrium is crucial for calculating the concentration of hydroxide ions in the solution.
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pH, pOH, and Their Relationship

pH and pOH are measures of the acidity and basicity of a solution, respectively. They are related by the equation pH + pOH = 14 at 25°C. The pH is calculated from the concentration of hydrogen ions (H+), while pOH is derived from the concentration of hydroxide ions (OH-). This relationship is essential for determining the pH and pOH of the ammonia solution.
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Equilibrium Constant (Kb) for Ammonia

The base dissociation constant (Kb) quantifies the strength of a weak base like ammonia in water. For ammonia, Kb is approximately 1.8 x 10^-5. This constant is used in the equilibrium expression to calculate the concentration of OH- ions in the solution, which is necessary for finding the pH and pOH values.
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