Textbook Question
For each of the following compounds (here shown in their acidic forms), write the form that predominates in a solution with a pH = 5.5:
i. HON+H3 (pKa = 6.0)
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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 40
Bruice 8th EditionCh. 2 - Acids and Bases: Central to Understanding Organic ChemistryProblem 40Chapter 3, Problem 40
As long as the pH is not less than ___________, at least 50% of a protonated amine with a pKa value of 10.4 will be in its neutral, nonprotonated form.
Verified step by step guidance1
Understand the relationship between pH, pKa, and the protonation state of an amine. The Henderson-Hasselbalch equation is key here: , where [A^-] is the concentration of the deprotonated (neutral) form and [HA] is the concentration of the protonated form.
Recognize that the problem asks for the pH at which at least 50% of the amine is in its neutral, nonprotonated form. This means the ratio of [A^-] to [HA] is 1:1.
Substitute the ratio [A^-]/[HA] = 1 into the Henderson-Hasselbalch equation. The logarithm of 1 is 0, so the equation simplifies to .
Identify the pKa value given in the problem, which is 10.4. This means that when the pH equals 10.4, 50% of the amine will be in its neutral form.
Conclude that the pH must not be less than 10.4 for at least 50% of the protonated amine to be in its neutral, nonprotonated form.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
pKa and pH Relationship
The pKa of a compound is the pH at which half of the species are protonated and half are deprotonated. For a weak acid or base, if the pH is below the pKa, the protonated form predominates; if above, the deprotonated form is favored. Understanding this relationship is crucial for predicting the ionization state of amines in solution.
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Protonated vs. Nonprotonated Forms
A protonated amine carries a positive charge due to the addition of a proton (H+), while its nonprotonated form is neutral. The balance between these forms is influenced by the pH of the solution relative to the pKa of the amine. Recognizing this distinction helps in determining the predominant form of the amine at a given pH.
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Henderson-Hasselbalch Equation
The Henderson-Hasselbalch equation relates pH, pKa, and the ratio of protonated to nonprotonated species in a solution. It is expressed as pH = pKa + log([A-]/[HA]). This equation is essential for calculating the pH at which a specific percentage of an amine is in its neutral form, aiding in the answer to the question posed.
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Related Practice
Textbook Question
Indicate whether an alcohol (ROH) with a pKa value of 15 has more charged or more neutral molecules in a solution with the pH values given in Problem 41.
3. pH = 7
4. pH = 10
5. pH = 13
1
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Textbook Question
For each of the following compounds (here shown in their acidic forms), write the form that predominates in a solution with a pH = 5.5:
e. +NH4 (pKa = 9.4)
f. HC≡N (pKa = 9.1)
1
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Textbook Question
Indicate whether an alcohol (ROH) with a pKa value of 15 has more charged or more neutral molecules in a solution with the pH values given in Problem 41.
1. pH = 1
2. pH = 3
3. pH = 5
1
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Textbook Question
Indicate whether a protonated amine (RN+H3) with a pKa value of 9 has more charged or more neutral molecules in a solution with the pH values given in Problem 41.
1. pH = 1
2. pH = 3
3. pH = 5
4. pH = 7
5. pH = 10
6. pH = 13
3
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Textbook Question
For each of the following compounds (here shown in their acidic forms), write the form that predominates in a solution with a pH = 5.5:
g. HNO2 (pKa = 3.4)
h. HNO3 (pKa = −1.3)
2
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