Ephedrine, a central nervous system stimulant, is used in nasal sprays as a decongestant. This compound is a weak organic base: C10H15ON1aq2 + H2O1l2 Δ C10H15ONH+1aq2 + OH-1aq2 A 0.035 M solution of ephedrine has a pH of 11.33. (b) Calculate Kb for ephedrine.
Ch.16 - Acid-Base Equilibria
Chapter 16, Problem 77a
Given that Ka for acetic acid is 1.8 * 10-5 and that for hypochlorous acid is 3.0 * 10-8, which is the stronger acid?
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Acid Dissociation Constant (Ka)
The acid dissociation constant (Ka) quantifies the strength of an acid in solution. It is defined as the equilibrium constant for the dissociation of an acid into its conjugate base and a proton. A higher Ka value indicates a stronger acid, as it means the acid dissociates more completely in solution.
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Characteristics of Ka and Kb
Comparing Acid Strengths
To determine which acid is stronger, one can compare their Ka values directly. The acid with the larger Ka value is considered the stronger acid because it indicates a greater tendency to donate protons. In this case, comparing the Ka values of acetic acid (1.8 * 10^-5) and hypochlorous acid (3.0 * 10^-8) will reveal which acid is stronger.
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Comparing Binary Acid Strength
Conjugate Acid-Base Pairs
Every acid has a corresponding conjugate base formed when it donates a proton. The strength of an acid is inversely related to the strength of its conjugate base; a strong acid has a weak conjugate base. Understanding this relationship helps in predicting the behavior of acids and bases in chemical reactions and their relative strengths.
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Related Practice
Textbook Question
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Textbook Question
Codeine 1C18H21NO32 is a weak organic base. A 5.0 * 10-3M solution of codeine has a pH of 9.95. Calculate the value of Kb for this substance. What is the pKb for this base?
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Textbook Question
Use the acid-dissociation constants in Table 16.3 to arrange these oxyanions from strongest base to weakest: SO42-, CO32-, SO32-, and PO43-.
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Textbook Question
Which is the stronger base, the acetate ion or the hypochlorite ion?
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Textbook Question
Calculate Kb values for CH3COO- and ClO-.
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Textbook Question
Given that Kb for ammonia is 1.8 * 10-5 and that for hydroxylamine is 1.1 * 10-8, which is the stronger base?
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