Ammonia 1NH32 has base dissociation constant 1Kb2 of 1.8 * 10-5. What is the concentration of an aqueous ammonia solution that has a pH of 11.68? (LO 16.11) (a) 0.28 M (b) 3.6 M (c) 9.0 * 10-3 M (d) 1.3 M

Guida verificata passo dopo passo

First, understand that ammonia (NH_3) is a weak base and its dissociation in water can be represented by the equation: NH_3 + H_2O \(\rightleftharpoons\) NH_4^+ + OH^-.

Next, use the given pH to find the pOH. Since pH + pOH = 14, calculate pOH = 14 - 11.68.

Convert the pOH to the hydroxide ion concentration [OH^-] using the formula: [OH^-] = 10^{-\(\text{pOH}\)}.

Apply the base dissociation constant (K_b) expression for ammonia: K_b = \(\frac{[NH_4^+][OH^-]}{[NH_3]}\). Since [NH_4^+] = [OH^-] at equilibrium, substitute [OH^-] into the K_b expression.

Rearrange the K_b expression to solve for the initial concentration of ammonia [NH_3]: [NH_3] = \(\frac{[OH^-]^2}{K_b}\).

Risposta video verificata per un problema simile:

Questa soluzione video è stata consigliata dai nostri tutor come utile per risolvere questo problema.

Durata del video:

Concetti chiave

Ecco i concetti essenziali che devi comprendere per rispondere correttamente alla domanda.

Base Dissociation Constant (Kb)

The base dissociation constant (Kb) quantifies the strength of a base in solution. It is defined as the equilibrium constant for the reaction in which a base accepts a proton from water, forming its conjugate acid and hydroxide ions. A higher Kb value indicates a stronger base, while a lower value suggests a weaker base. In this case, ammonia has a Kb of 1.8 x 10^-5, indicating it is a weak base.

Video consigliato:

Percorso guidato

03:50

Characteristics of Ka and Kb

pH and pOH Relationship

pH is a measure of the acidity or basicity of a solution, defined as the negative logarithm of the hydrogen ion concentration. The pOH is similarly defined for hydroxide ions. The relationship between pH and pOH is given by the equation pH + pOH = 14 at 25°C. For a solution with a pH of 11.68, the pOH can be calculated, which is essential for determining the concentration of hydroxide ions in the solution.

Video consigliato:

Percorso guidato

02:09

pH and pOH Calculations

Concentration of Hydroxide Ions [OH-]

The concentration of hydroxide ions ([OH-]) in a solution can be derived from the pOH value. Once the pOH is calculated from the pH, the concentration of hydroxide ions can be found using the formula [OH-] = 10^(-pOH). This concentration is crucial for applying the Kb expression to find the concentration of ammonia in the solution, as it relates to the equilibrium established when ammonia dissociates in water.

Video consigliato:

Percorso guidato