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 43d
Bruice 8th EditionCh. 2 - Acids and Bases: Central to Understanding Organic ChemistryProblem 43dChapter 3, Problem 43d
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.
d. Draw the structure of alanine in a solution at pH = 12.
Verified step by step guidance1
Step 1: Understand the structure of alanine. Alanine is an amino acid with a carboxylic acid group (-COOH) and a protonated amine group (-NH3+). The pKa values provided are 2.34 for the carboxylic acid group and 9.69 for the protonated amine group.
Step 2: Analyze the pH of the solution. At pH = 12, the solution is basic, which means it is above the pKa values of both functional groups. This will affect the protonation state of the groups.
Step 3: Determine the state of the carboxylic acid group. Since the pH (12) is much higher than the pKa of the carboxylic acid group (2.34), the carboxylic acid group will lose its proton and exist as a carboxylate ion (-COO⁻).
Step 4: Determine the state of the amine group. Since the pH (12) is higher than the pKa of the protonated amine group (9.69), the amine group will lose its proton and exist as a neutral amine (-NH2).
Step 5: Draw the structure of alanine at pH = 12. The structure will have a carboxylate group (-COO⁻) and a neutral amine group (-NH2), along with the methyl group (-CH3) attached to the alpha carbon.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Amino Acids
Amino acids are organic compounds that serve as the building blocks of proteins. Each amino acid contains a central carbon atom bonded to an amino group (–NH2), a carboxylic acid group (–COOH), a hydrogen atom, and a variable side chain (R group) that determines its unique properties. Understanding the structure and function of amino acids is essential for grasping their behavior in different pH environments.
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Standard Amino Acids
pKa and Ionization
pKa is a measure of the acidity of a proton in a molecule, indicating the pH at which half of the species are deprotonated. In the context of amino acids, the pKa values of the carboxylic acid and the amine groups determine their ionization state at a given pH. At pH 12, which is above the pKa of the carboxylic acid, this group will be deprotonated, while the amine group will remain protonated if its pKa is higher than 12.
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Zwitterion Form
A zwitterion is a molecule that has both positive and negative charges but is overall neutral. In amino acids, at physiological pH, they often exist as zwitterions, where the amino group is protonated (–NH3+) and the carboxylic acid group is deprotonated (–COO–). At pH 12, alanine will predominantly exist in a form where the carboxylic acid is deprotonated, leading to a net negative charge on the molecule.
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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
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.
c. Draw the structure of alanine in a solution at physiological pH (pH 7.4).
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
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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
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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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