Textbook Question
Butyric acid, the compound responsible for the unpleasant odor and taste of sour milk, has a pKa value of 4.82. What is its Ka value? Is it a stronger acid or a weaker acid than vitamin C?
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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 5ab
Bruice 8th EditionCh. 2 - Acids and Bases: Central to Understanding Organic ChemistryProblem 5abChapter 3, Problem 5ab
a. Which is a stronger acid: one with a pKa of 5.2 or one with a pKa of 5.8?
b. Which is a stronger acid: one with an acid dissociation constant of 3.4 × 10−3 or one with an acid dissociation constant of 2.1 × 10−4?
Verified step by step guidance1
Step 1: Understand the relationship between pKa and acid strength. The lower the pKa value, the stronger the acid. This is because pKa is inversely related to the acid dissociation constant (Ka), which measures the extent of ionization of the acid in solution.
Step 2: Compare the pKa values given in part (a). The acid with a pKa of 5.2 is lower than the acid with a pKa of 5.8, indicating that the acid with a pKa of 5.2 is stronger.
Step 3: Understand the relationship between Ka and acid strength for part (b). The higher the Ka value, the stronger the acid. This is because a larger Ka indicates greater ionization of the acid in solution.
Step 4: Compare the Ka values given in part (b). The acid with a Ka of 3.4×10⁻³ is larger than the acid with a Ka of 2.1×10⁻⁴, indicating that the acid with a Ka of 3.4×10⁻³ is stronger.
Step 5: Summarize the findings: For part (a), the acid with a pKa of 5.2 is stronger. For part (b), the acid with a Ka of 3.4×10⁻³ is stronger. This demonstrates the inverse relationship between pKa and Ka when determining acid strength.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
pKa and Acid Strength
The pKa value is a logarithmic measure of the acidity of a substance, where a lower pKa indicates a stronger acid. This is because pKa is derived from the acid dissociation constant (Ka), which quantifies the extent to which an acid donates protons in solution. Therefore, comparing pKa values allows us to determine which acid is stronger based on their numerical values.
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Identifying pKa values
Acid Dissociation Constant (Ka)
The acid dissociation constant (Ka) is a quantitative measure of the strength of an acid in solution. It represents the equilibrium constant for the dissociation of an acid into its conjugate base and a proton. A larger Ka value indicates a stronger acid, as it signifies a greater tendency to lose protons, making it essential for comparing acid strengths directly.
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02:19The relationship between equilibrium constant and pKa.
Relationship Between pKa and Ka
The relationship between pKa and Ka is expressed by the equation pKa = -log(Ka). This means that as the Ka increases, the pKa decreases, reinforcing the idea that stronger acids have lower pKa values. Understanding this relationship is crucial for interpreting acid strength comparisons, as it allows for the conversion between the two measures and aids in determining which acid is stronger.
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02:19The relationship between equilibrium constant and pKa.
Related Practice
Textbook Question
What is the conjugate base of each of the following?
1. NH3
2. HBr
3. HNO3
4. H2O
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Textbook Question
Antacids are compounds that neutralize stomach acid. Write the equations that show how Milk of Magnesia, Alka-Seltzer, and Tums remove excess acid.
a. Milk of Magnesia: Mg(OH)2
b. Alka-Seltzer: KHCO3 and NaHCO3
c. Tums: CaCO3
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Textbook Question
What is the conjugate acid of each of the following?
1. NH3
2. Cl−
3. HO−
4. H2O
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Textbook Question
An acid has a Ka of 4.53 × 10−6 in water. What is its Keq for reaction with water in a dilute solution? ([H2O] = 55.5 M)
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Textbook Question
Consider the following reaction:
HBr + -C≡N ⇌ Br− + HC≡N
g. What is the conjugate base of the acid on the right?
h. What is the conjugate acid of the base on the right?
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