Textbook Question
At what pH is the concentration of a compound, with a pKa = 8.4, 100 times greater in its acidic form than in its basic form? At what pH is 50% of a compound, with a pKa = 7.3, in its basic form?
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Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry
Bruice8th EditionOrganic ChemistryISBN: 9780135213711
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Table of contents
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 1)31
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 2)65
- Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry84
- Ch. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and Structure183
- Ch. 4 - Isomers: The Arrangement of Atoms in Space121
- Ch. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and Kinetics83
- Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions175
- Ch. 7 - The Reactions of Alkynes • An Introduction to Multistep Synthesis119
- Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene148
- Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides212
- Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds131
- Ch. 11 - Organometallic Compounds60
- Ch. 12 - Radicals90
- Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy62
- Ch. 14 - NMR Spectroscopy95
- Ch. 15 - Reactions of Carboxylic Acids and Carboxylic Acid Derivatives123
- Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives141
- Ch. 17 - Reactions at the Alpha-Carbon101
- Ch. 18 - Reactions of Benzene and Substituted Benzenes144
- Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds49
- Ch. 20 - The Organic Chemistry of Carbohydrates80
- Ch. 21 - Amino Acids, Peptides, and Proteins57
- Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions35
- Ch. 23 - The Organic Chemistry of the Coenzymes—Compounds Derived from Vitamins1
- Ch. 28 - Pericyclic Reactions58
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Bruice 8th EditionCh. 2 - Acids and Bases: Central to Understanding Organic ChemistryProblem 46b
Bruice 8th EditionCh. 2 - Acids and Bases: Central to Understanding Organic ChemistryProblem 46bChapter 3, Problem 46b
For each of the following compounds, indicate the pH at which
b. more than 99% of the compound is in a form that possesses a charge.
1. CH3CH2COOH (pKa = 4.9)
2. CH3N+H3 (pKa = 10.7)
Verified step by step guidance1
Step 1: Understand the problem. The question asks for the pH at which more than 99% of the compound is in a charged form. This involves determining whether the compound is protonated or deprotonated based on its pKa value and the pH of the solution.
Step 2: Recall the Henderson-Hasselbalch equation: . This equation relates the pH, pKa, and the ratio of the concentrations of the deprotonated form ([A⁻]) to the protonated form ([HA]).
Step 3: For more than 99% of the compound to be in the charged form, the ratio of [A⁻] to [HA] (or vice versa, depending on the compound) must be at least 99:1. This corresponds to a difference of 2 in the logarithmic scale (log(99) ≈ 2).
Step 4: For CH3CH2COOH (pKa = 4.9), the charged form is CH3CH2COO⁻. To achieve 99% deprotonation, the pH must be at least 2 units higher than the pKa. Use the relationship: . Substitute the pKa value to find the pH.
Step 5: For CH3N⁺H3 (pKa = 10.7), the charged form is CH3N⁺H3. To achieve 99% protonation, the pH must be at least 2 units lower than the pKa. Use the relationship: . Substitute the pKa value to find the pH.
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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. The pKa value indicates the strength of an acid; lower pKa values correspond to stronger acids. Understanding this equilibrium is crucial for predicting the protonation state of compounds at different pH levels.
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04:00
Determining Acid/Base Equilibrium
pH and Charge
pH is a measure of the hydrogen ion concentration in a solution, influencing the protonation state of acidic and basic functional groups. For a compound to be more than 99% charged, the pH must be significantly lower than the pKa for acids or higher than the pKa for bases. This relationship helps determine the predominant form of a compound in solution.
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01:34Calculating formal and net charge.
Henderson-Hasselbalch Equation
The Henderson-Hasselbalch equation relates pH, pKa, and the ratio of the concentrations of the deprotonated and protonated forms of an acid. It is expressed as pH = pKa + log([A-]/[HA]). This equation is essential for calculating the pH at which a specific percentage of a compound exists in its charged form, aiding in the analysis of the compounds in the question.
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05:02Breaking down the different terms of the Gibbs Free Energy equation.
Related Practice
Textbook Question
For each of the following compounds, indicate the pH at which
a. 50% of the compound is in a form that possesses a charge.
1. CH3CH2COOH (pKa = 4.9)
2. CH3N+H3 (pKa = 10.7)
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Textbook Question
Given the data in Problem 47:
b. What pH would you make the water layer to cause the carboxylic acid to dissolve in the water layer and the amine to dissolve in the ether layer?
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Textbook Question
Given the data in Problem 47:
a. What pH would you make the water layer to cause the carboxylic acid to dissolve in the water layer and the amine to dissolve in the ether layer?
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Textbook Question
Write the equation that shows how a buffer made by dissolving CH3COOH and CH3COO−Na+ in water prevents the pH of a solution from changing appreciably when
a. a small amount of H+ is added to the solution.
b. a small amount of HO− is added to the solution.
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Textbook Question
At what pH is the concentration of a compound, with a pKa = 4.6, 10 times greater in its basic form than in its acidic form?
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