Textbook Question
If a solution of HF 1Ka = 6.8 * 10-42 has a pH of 3.65, calculate the concentration of hydrofluoric acid.
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Ch.16 - Acid-Base Equilibria
Brown15th EditionChemistry: The Central ScienceISBN: 9780137542970
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Table of contents
- Ch.1 - Introduction: Matter, Energy, and Measurement111
- Ch.2 - Atoms, Molecules, and Ions166
- Ch.3 - Chemical Reactions and Reaction Stoichiometry138
- Ch.4 - Reactions in Aqueous Solution127
- Ch.5 - Thermochemistry104
- Ch.6 - Electronic Structure of Atoms109
- Ch.7 - Periodic Properties of the Elements107
- Ch.8 - Basic Concepts of Chemical Bonding102
- Ch.9 - Molecular Geometry and Bonding Theories120
- Ch.10 - Gases122
- Ch.11 - Liquids and Intermolecular Forces79
- Ch.12 - Solids and Modern Materials102
- Ch.13 - Properties of Solutions99
- Ch.14 - Chemical Kinetics153
- Ch.15 - Chemical Equilibrium83
- Ch.16 - Acid-Base Equilibria109
- Ch.17 - Additional Aspects of Aqueous Equilibria117
- Ch.18 - Chemistry of the Environment60
- Ch.19 - Chemical Thermodynamics109
- Ch.20 - Electrochemistry113
- Ch.21 - Nuclear Chemistry79
- Ch.22 - Chemistry of the Nonmetals52
- Ch.23 - Transition Metals and Coordination Chemistry57
- Ch.24 - The Chemistry of Life: Organic and Biological Chemistry7
Brown15th EditionChemistry: The Central ScienceISBN: 9780137542970Not the one you use?Change textbook
Chapter 16, Problem 55
Lactic acid CH3CH(OH)COOH has one acidic hydrogen. A 0.10 M solution of lactic acid has a pH of 2.44. Calculate Ka.
Verified step by step guidance1
Identify the given information: The concentration of lactic acid is 0.10 M, and the pH of the solution is 2.44.
Calculate the concentration of hydrogen ions [H⁺] using the pH value: [H⁺] = 10^(-pH). Substitute the given pH value to find [H⁺].
Write the expression for the acid dissociation constant (Ka) for lactic acid: Ka = [H⁺][A⁻]/[HA], where [A⁻] is the concentration of the conjugate base and [HA] is the concentration of the undissociated acid.
Assume that the initial concentration of lactic acid [HA] is 0.10 M and that the change in concentration due to dissociation is equal to [H⁺]. Therefore, [A⁻] = [H⁺] and [HA] = 0.10 - [H⁺].
Substitute the values of [H⁺], [A⁻], and [HA] into the Ka expression and solve for Ka.
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 an acid and its conjugate base in a solution. For weak acids like lactic acid, this equilibrium can be described by the dissociation reaction, where the acid donates a proton (H+) to water, forming its conjugate base and hydronium ions. Understanding this concept is crucial for calculating the acid dissociation constant (Ka).
Recommended video:
Guided course
05:11
Triprotic Acid Equilibrium
pH and Hydronium Ion Concentration
pH is a measure of the acidity of a solution, defined as the negative logarithm of the hydronium ion concentration (H3O+). A lower pH indicates a higher concentration of H3O+. In this case, the pH of 2.44 corresponds to a specific concentration of hydronium ions, which is essential for determining the degree of dissociation of lactic acid and subsequently calculating Ka.
Recommended video:
Guided course
06:25Hydronium Ion Concentration Example
Acid Dissociation Constant (Ka)
The acid dissociation constant (Ka) quantifies the strength of a weak acid in solution. It is defined as the ratio of the concentration of the products (the conjugate base and hydronium ions) to the concentration of the undissociated acid at equilibrium. Calculating Ka involves using the concentrations derived from the initial concentration of the acid and the change in concentration due to dissociation, which is influenced by the pH of the solution.
Recommended video:
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03:50Characteristics of Ka and Kb
Related Practice
Textbook Question
Calculate the concentration of an aqueous solution of Ca1OH22 that has a pH of 10.05.
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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.
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Textbook Question
Write the chemical equation and the Ka expression for the acid dissociation of each of the following acids in aqueous solution. First show the reaction with H+(a)q as a product and then with the hydronium ion: (a) C6H5COOH (b) HCO3-
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