The pH of a 2.1 × 10^-3 M solution of a weak base is 9.87. Calculate K_b for this base. A) 2.6 × 10^-6 B) 1.2 × 10^-4 C) 6.4 × 10^-8 D) 8.7 × 10^-18 E) none of these

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Quizplus · Accepted Answer

The correct answer is A because the pH of a solution is a measure of its acidity or basicity. The pH of a solution is calculated using the following equation:pH = -log[H+],where [H+] is the molar concentration of hydrogen ions in the solution. The pOH of a solution is a measure of its basicity and is calculated using the following equation:pOH = -log[OH-],where [OH-] is the molar concentration of hydroxide ions in the solution. The pH and pOH of a solution are related by the following equation:pH + pOH = 14.In this problem, we are given the pH of a solution of a weak base and asked to calculate the Kb for the base. The Kb for a weak base is a measure of its strength as a base and is calculated using the following equation:Kb = [OH-]^2/[B],where [OH-] is the molar concentration of hydroxide ions in the solution and [B] is the molar concentration of the weak base.To calculate the Kb for the weak base in this problem, we first need to calculate the [OH-] in the solution. We can do this using the pH of the solution and the equation:pH = -log[H+].Substituting the given pH value into this equation, we get:9.87 = -log[H+].Solving for [H+], we get:[H+] = 1.34 × 10^-10 M.Now that we have the [H+], we can use the equation:pOH = 14 - pH,to calculate the pOH of the solution:pOH = 14 - 9.87 = 4.13.Now that we have the pOH, we can use the equation:pOH = -log[OH-],to calculate the [OH-] in the solution:[OH-] = 7.41 × 10^-5 M.Now that we have the [OH-], we can use the equation:Kb = [OH-]^2/[B],to calculate the Kb for the weak base:Kb = (7.41 × 10^-5 M)^2/(2.1 × 10^-3 M) = 2.6 × 10^-6.Therefore, the Kb for the weak base in this problem is 2.6 × 10^-6.

The PH of a 2