Textbook Question
An acid solution with a concentration of 0.500 M has a pH = 3.21. What is the Ka of the acid? (LO 16.8) (a) 1.2 * 10-5 (b) 1.7 * 10-6 (c) 7.6 * 10-7 (d) 5.4 * 10-3
Ch.16 - Aqueous Equilibria: Acids & Bases
Chapter 16, Problem 12
Using values of Kb in Appendix C, calculate values of Ka for each of the following ions: (b) Hydroxylammonium ion, NH3OH+; (c) Anilinium ion, C6H5NH3+; (d) Pyridinium ion, C5H5NH+.
Verified step by step guidance1
Step 1: Understand the relationship between Ka and Kb. For a conjugate acid-base pair, the product of the acid dissociation constant (Ka) and the base dissociation constant (Kb) is equal to the ion product of water (Kw), which is 1.0 x 10^-14 at 25°C. This can be expressed as: Ka * Kb = Kw.
Step 2: Identify the conjugate base for each ion. For hydroxylammonium ion (NH3OH+), the conjugate base is hydroxylamine (NH2OH). For anilinium ion (C6H5NH3+), the conjugate base is aniline (C6H5NH2). For pyridinium ion (C5H5NH+), the conjugate base is pyridine (C5H5N).
Step 3: Look up the Kb values for the conjugate bases in Appendix C. These values are necessary to calculate the Ka values for the corresponding conjugate acids.
Step 4: Calculate the Ka for each ion using the formula: Ka = Kw / Kb. Substitute the known values of Kw and the Kb for each conjugate base into the formula to find the Ka for each ion.
Step 5: Verify the units and ensure that the calculated Ka values are consistent with the expected order of magnitude for weak acids, typically ranging from 10^-1 to 10^-14.
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 acids and bases in a solution, characterized by the dissociation of acids into protons (H+) and their conjugate bases. The strength of an acid is quantified by its acid dissociation constant (Ka), while the strength of a base is represented by its base dissociation constant (Kb). Understanding this equilibrium is crucial for calculating the Ka values from given Kb values.
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Triprotic Acid Equilibrium
Relationship Between Ka and Kb
The relationship between the acid dissociation constant (Ka) and the base dissociation constant (Kb) is given by the equation Ka × Kb = Kw, where Kw is the ion product of water (1.0 × 10^-14 at 25°C). This relationship allows for the conversion of Kb values of basic ions into their corresponding Ka values, facilitating the analysis of their acidic properties.
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03:01Ka and Kb Relationship
Conjugate Acid-Base Pairs
Conjugate acid-base pairs consist of an acid and its corresponding base that differ by a single proton. For example, when a base accepts a proton, it forms its conjugate acid. Recognizing these pairs is essential for understanding the behavior of ions in solution, as it helps in determining the strength of acids and bases and their respective dissociation constants.
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01:30Conjugate Acid-Base Pairs
Related Practice
Textbook Question
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
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Textbook Question
Consider the reaction: SO2 + OH- S HSO3-. Which reaction scheme shows the correct use of the curved arrow notation representing thedonation of an electron pair and the correct labeling of the Lewis acid and Lewis base? (LO 16.14)(a) (b) (c) (d)