Find the pH and percent ionization of each HF solution. (Ka for HF is 6.8 * 10^-4.) a. 0.250 M HF b. 0.100 M HF c. 0.050 M HF.

Name: Chemistry: A Molecular Approach
Author: Tro
ISBN: 9780134112831

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Identify the given data: the concentration of HF and its acid dissociation constant (Ka = 6.8 \(\times\) 10^{-4}).

Write the balanced chemical equation for the ionization of HF: \[ \text{HF} \rightleftharpoons \text{H}^+ + \text{F}^- \].

Set up an ICE (Initial, Change, Equilibrium) table to determine the concentrations of the species at equilibrium.

Use the expression for the acid dissociation constant: \[ K_a = \frac{[\text{H}^+][\text{F}^-]}{[\text{HF}]} \] and substitute the equilibrium concentrations from the ICE table.

Solve the quadratic equation for \([\text{H}^+]\), calculate the pH using \( \text{pH} = -\log[\text{H}^+] \), and determine the percent ionization using \( \frac{[\text{H}^+]}{[\text{HF}]_0} \times 100\% \).

Concetti chiave

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Acid-Base Equilibrium

Acid-base equilibrium refers to the balance between the concentrations of an acid and its conjugate base in a solution. For weak acids like hydrofluoric acid (HF), this equilibrium is described by the acid dissociation constant (Ka), which quantifies the extent to which the acid donates protons (H+) to the solution. Understanding this concept is crucial for calculating pH and percent ionization.

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Triprotic Acid Equilibrium

pH Calculation

pH is a measure of the acidity or basicity of a solution, defined as the negative logarithm of the hydrogen ion concentration (pH = -log[H+]). For weak acids, the pH can be calculated using the concentration of the acid and its dissociation constant (Ka). This involves setting up an equilibrium expression and solving for [H+], which is then used to find the pH.

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pH Calculation Example

Percent Ionization

Percent ionization is a measure of the degree to which a weak acid dissociates in solution, expressed as the ratio of the concentration of ionized acid to the initial concentration of the acid, multiplied by 100. It provides insight into the strength of the acid; weaker acids have lower percent ionization. This concept is essential for comparing the ionization of different concentrations of HF in the given problem.

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