Textbook Question
a. Without using a calculator, estimate the pH of each of the following solutions:
1. [HO−] = 3.2 × 10−5
2. [H3O+] = 8.3 × 10−1
3. [H3O+] = 1.7 × 10−3
b. Determine the exact pH, using a calculator.
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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 72b
Bruice 8th EditionCh. 2 - Acids and Bases: Central to Understanding Organic ChemistryProblem 72bChapter 3, Problem 72b
Citrus fruits are rich in citric acid, a compound with three COOH groups. Explain the following:
b. The third pKa is greater than the pKa of acetic acid.
Verified step by step guidance1
Step 1: Understand the structure of citric acid. Citric acid is a tricarboxylic acid with three carboxylic acid (-COOH) groups. Each -COOH group has a different pKa value due to the influence of the molecule's structure and the interactions between the groups.
Step 2: Compare the third pKa of citric acid (5.8) with the pKa of acetic acid (4.76). The pKa value indicates the strength of an acid; a higher pKa means the acid is weaker. The third -COOH group in citric acid is less acidic than acetic acid.
Step 3: Consider the electronic effects within citric acid. When the first and second -COOH groups lose their protons, the molecule becomes negatively charged. This negative charge creates electrostatic repulsion, making it harder for the third -COOH group to lose its proton, thus increasing its pKa value.
Step 4: Compare acetic acid's structure. Acetic acid has only one -COOH group, so there are no additional negative charges or intramolecular interactions to stabilize the conjugate base. This makes acetic acid more acidic than the third -COOH group in citric acid.
Step 5: Summarize the reasoning. The third pKa of citric acid is greater than the pKa of acetic acid because the negative charges on the conjugate base of citric acid after losing two protons create repulsion, making it harder for the third proton to dissociate. This effect is absent in acetic acid, which has only one -COOH group.
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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
pKa is a measure of the acidity of a compound, indicating the strength of an acid in solution. A lower pKa value corresponds to a stronger acid, as it reflects a greater tendency to donate protons (H+ ions). Understanding pKa is essential for comparing the acidity of different compounds, such as citric acid and acetic acid.
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Identifying pKa values
Citric Acid Structure
Citric acid is a tricarboxylic acid, meaning it contains three carboxyl (COOH) groups. The presence of multiple acidic protons allows for multiple dissociation steps, each with its own pKa value. The structure of citric acid influences its acidity, as the electron-withdrawing effects of the other carboxyl groups can stabilize the negative charge on the conjugate base formed after deprotonation.
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Comparative Acidity of Acids
When comparing the acidity of citric acid and acetic acid, it is important to consider the number of acidic protons and the stability of their conjugate bases. The third pKa of citric acid being greater than that of acetic acid suggests that the third proton is less easily lost, indicating that the corresponding conjugate base is less stable compared to that of acetic acid, which has only one acidic proton.
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Related Practice
Textbook Question
Given that pH + pOH = 14 and that the concentration of water in a solution of water is 55.5 M, show that the pKa of water is 15.7. (Hint: pOH=−log [HO−])
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Textbook Question
Citrus fruits are rich in citric acid, a compound with three COOH groups. Explain the following:
a. The first pKa (for the COOH group in the center of the molecule) is lower than the pKa of acetic acid.
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Textbook Question
You are planning to carry out a reaction that produces protons. The reaction will be buffered at pH = 10.5. Would it be better to use a protonated methylamine/methylamine buffer or a protonated ethylamine/ethylamine buffer? (pKa of protonated methylamine = 10.7; pKa of protonated ethylamine = 11.0)
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Textbook Question
How could you separate a mixture of the following compounds? The reagents available to you are water, ether, 1.0 M HCl, and 1.0 M NaOH.
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Textbook Question
If an acid with a pKa of 5.3 is in an aqueous solution of pH 5.7, what percentage of the acid is present in its acidic form?
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