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Ch.17 - Acids and Bases
Chapter 17, Problem 82c

For each strong base solution, determine [OH], [H3O+], pH, and pOH. c. 1.9×10–4 M KOH

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<strong>Step 1:</strong> Identify the strong base. Potassium hydroxide (KOH) is a strong base, which means it dissociates completely in water. Therefore, the concentration of OH⁻ ions is equal to the concentration of the KOH solution, which is 1.9 \times 10^{-4} \text{ M}.
<strong>Step 2:</strong> Calculate the concentration of H₃O⁺ ions. Use the water dissociation constant (K_w = 1.0 \times 10^{-14} \text{ at 25°C}) to find [H₃O⁺]. The relationship is given by: [H₃O⁺] = \frac{K_w}{[OH⁻]}.
<strong>Step 3:</strong> Calculate the pOH of the solution. The pOH is calculated using the formula: \text{pOH} = -\log[OH⁻].
<strong>Step 4:</strong> Calculate the pH of the solution. Use the relationship between pH and pOH: \text{pH} + \text{pOH} = 14. Therefore, \text{pH} = 14 - \text{pOH}.
<strong>Step 5:</strong> Summarize the results. You now have the values for [OH⁻], [H₃O⁺], pH, and pOH for the given KOH solution.

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Key Concepts

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

Strong Bases

Strong bases, such as potassium hydroxide (KOH), completely dissociate in water to produce hydroxide ions (OH-). This means that the concentration of the base in solution is equal to the concentration of OH- ions produced. Understanding this dissociation is crucial for calculating the concentrations of hydroxide and hydronium ions in the solution.
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pH and pOH Calculations

pH and pOH are logarithmic scales used to measure the acidity and basicity of a solution, respectively. The pH is calculated using the formula pH = -log[H3O+], while pOH is calculated as pOH = -log[OH-]. The relationship between pH and pOH is given by the equation pH + pOH = 14 at 25°C, which is essential for converting between these two measures.
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Ion Product of Water

The ion product of water (Kw) is a fundamental concept in acid-base chemistry, defined as Kw = [H3O+][OH-] = 1.0 x 10^-14 at 25°C. This relationship allows us to find the concentration of hydronium ions when the concentration of hydroxide ions is known, and vice versa. It is critical for determining the pH and pOH of a solution when dealing with strong bases.
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