Textbook Question
At what pH does 80% of the acid exist in its acidic 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 76a
Bruice 8th EditionCh. 2 - Acids and Bases: Central to Understanding Organic ChemistryProblem 76aChapter 3, Problem 76a
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?
Verified step by step guidance1
Identify the relationship between pH, pKa, and the ratio of the acidic form (HA) to the conjugate base (A⁻) using the Henderson-Hasselbalch equation: \( \text{pH} = \text{pKa} + \log \left( \frac{[A^-]}{[HA]} \right) \).
Rearrange the Henderson-Hasselbalch equation to solve for the ratio \( \frac{[A^-]}{[HA]} \): \( \frac{[A^-]}{[HA]} = 10^{\text{pH} - \text{pKa}} \).
Substitute the given values for pH (5.7) and pKa (5.3) into the equation: \( \frac{[A^-]}{[HA]} = 10^{5.7 - 5.3} \).
Once the ratio \( \frac{[A^-]}{[HA]} \) is determined, calculate the fraction of the acid in its acidic form (HA) using the formula: \( \text{Fraction of HA} = \frac{1}{1 + \frac{[A^-]}{[HA]}} \).
Convert the fraction of HA into a percentage by multiplying by 100: \( \text{Percentage of HA} = \text{Fraction of HA} \times 100 \).
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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 an acid is a measure of its strength, indicating the pH at which half of the acid is dissociated. A lower pKa value means a stronger acid. The pH of a solution reflects the concentration of hydrogen ions; when pH is higher than pKa, the acid is more likely to be in its deprotonated (conjugate base) form.
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Identifying pKa values
Henderson-Hasselbalch Equation
The Henderson-Hasselbalch equation relates pH, pKa, and the ratio of the concentrations of the deprotonated and protonated forms of an acid. It is expressed as pH = pKa + log([A-]/[HA]), where [A-] is the concentration of the conjugate base and [HA] is the concentration of the acid. This equation is essential for calculating the proportions of the acid in different forms at a given pH.
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Percentage of Acidic Form
To determine the percentage of an acid present in its acidic form, one can use the ratio derived from the Henderson-Hasselbalch equation. By calculating the ratio of [HA] to the total concentration of acid ([HA] + [A-]), the percentage of the acid in its protonated form can be expressed as ( [HA] / ([HA] + [A-]) ) × 100%. This calculation is crucial for understanding the acid's behavior in solution.
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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
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
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.
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