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 46a
Bruice 8th EditionCh. 2 - Acids and Bases: Central to Understanding Organic ChemistryProblem 46aChapter 3, Problem 46a
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)
Verified step by step guidance1
Step 1: Understand the concept of pKa and its relationship to pH. The pKa value of a compound is the pH at which 50% of the compound exists in its protonated form and 50% in its deprotonated form. This is the point where the compound is in equilibrium between its charged and uncharged forms.
Step 2: For CH3CH2COOH (pKa = 4.9), recognize that this is a carboxylic acid. At pH = pKa, 50% of the carboxylic acid will be in its deprotonated form (CH3CH2COO⁻, which is charged) and 50% will remain in its protonated form (CH3CH2COOH, which is neutral). Therefore, the pH at which 50% of the compound is charged is equal to its pKa value.
Step 3: For CH3N+H3 (pKa = 10.7), recognize that this is an ammonium ion. At pH = pKa, 50% of the ammonium ion will be in its deprotonated form (CH3NH2, which is neutral) and 50% will remain in its protonated form (CH3N+H3, which is charged). Therefore, the pH at which 50% of the compound is charged is equal to its pKa value.
Step 4: Summarize the relationship for both compounds: The pH at which 50% of the compound is in a charged form is equal to the pKa value of the compound. This is a direct application of the Henderson-Hasselbalch equation, which describes the ratio of protonated to deprotonated species at a given pH.
Step 5: To solve similar problems, always identify the functional group responsible for the charge, locate the pKa value, and understand that at pH = pKa, the compound is 50% charged and 50% uncharged. This principle applies universally to acids and bases in organic chemistry.
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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 deprotonated, meaning 50% exists in a charged form. This relationship is crucial for understanding acid-base equilibria, as it helps predict the protonation state of a compound at a given pH. For example, if the pH is equal to the pKa, the concentrations of the protonated and deprotonated forms are equal.
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07:45
Identifying pKa values
Acid-Base Equilibrium
Acid-base equilibrium describes the balance between protonated (acidic) and deprotonated (basic) forms of a compound in solution. The position of this equilibrium is influenced by the pH of the solution and the pKa of the compound. Understanding this concept allows for the prediction of the predominant form of a compound at specific pH levels, which is essential for determining the charge state.
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04:00Determining Acid/Base Equilibrium
Charged vs. Neutral Species
In organic chemistry, the charge of a species can significantly affect its reactivity and solubility. Charged species, such as carboxylate ions or ammonium ions, often have different physical and chemical properties compared to their neutral counterparts. Recognizing when a compound exists in a charged form versus a neutral form is vital for predicting its behavior in various chemical environments.
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01:34Calculating formal and net charge.
Related Practice
Textbook Question
A naturally occurring amino acid such as alanine has a group that is a carboxylic acid and a group that is a protonated amine. The pKa values of the two groups are shown.
e. Is there a pH at which alanine is uncharged (that is, neither group has a charge)?
f. At what pH does alanine have no net charge (that is, the amount of negative charge is the same as the amount of positive charge)?
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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
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)
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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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