If a solution of HF 1Ka = 6.8 * 10-42 has a pH of 3.65, calculate the concentration of hydrofluoric acid.

Verified step by step guidance

Identify the given values: the pH of the solution is 3.65 and the acid dissociation constant (Ka) for HF is 6.8 \(\times\) 10^{-42}.

Calculate the concentration of hydrogen ions [H^+] using the pH value: [H^+] = 10^{-pH}.

Set up the expression for the acid dissociation constant (Ka) for HF: Ka = \(\frac{[H^+][F^-]}{[HF]}\).

Assume that the initial concentration of HF is 'C' and that the change in concentration due to dissociation is 'x'. Therefore, [H^+] = x, [F^-] = x, and [HF] = C - x.

Substitute the values into the Ka expression: 6.8 \(\times\) 10^{-42} = \(\frac{x^2}{C - x}\). Solve for 'C' using the approximation that x is small compared to C.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.

Video duration:

Was this helpful?

Key Concepts

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

Acid-Base Equilibrium

Acid-base equilibrium refers to the balance between the concentrations of acids and their conjugate bases in a solution. In the case of 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 the concentration of HF based on its pH.

pH and pKa Relationship

The pH of a solution is a measure of its acidity, defined as the negative logarithm of the hydrogen ion concentration. The pKa, which is the negative logarithm of the Ka, provides a more convenient way to express the strength of an acid. The relationship between pH, pKa, and the concentrations of the acid and its conjugate base is described by the Henderson-Hasselbalch equation, which is essential for solving problems involving weak acids.

Concentration Calculations

Concentration calculations involve determining the amount of solute present in a given volume of solution. For weak acids, the concentration can be derived from the pH and the dissociation constant (Ka). By using the pH to find the concentration of hydrogen ions and applying the equilibrium expression for the dissociation of the acid, one can calculate the initial concentration of the acid in the solution.

Recommended video:

Guided course

07:35

Calculate Concentration of the Basic Form

Related Practice

Textbook Question

Calculate the pH of each of the following solutions (Ka and Kb values are given in Appendix D): (a) 0.095 M propionic acid (C₂H₅COOH) (b) 0.100 M hydrogen chromate ion (HCrO₄^-)

Textbook Question

A 0.100 M solution of chloroacetic acid 1ClCH2COOH2 is 11.0% ionized. Using this information, calculate 3ClCH2COO-4, 3H+4, 3ClCH2COOH4, and Ka for chloroacetic acid.

Textbook Question

The acid-dissociation constant for chlorous acid 1HClO22 is 1.1 * 10-2. Calculate the concentrations of H3O+, ClO2-, and HClO2 at equilibrium if the initial concentration of HClO2 is 0.0125 M.

Textbook Question

A 0.100 M solution of bromoacetic acid 1BrCH2COOH2 is 13.2% ionized. Calculate 3H+4, 3BrCH2COO-4, 3BrCH2COOH4 and Ka for bromoacetic acid.