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?
1706
views
Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry
Bruice8th EditionOrganic ChemistryISBN: 9780135213711
Not the one you use?Change textbookSelect a different textbook
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
All textbooks
Bruice 8th EditionCh. 2 - Acids and Bases: Central to Understanding Organic ChemistryProblem 45c
Bruice 8th EditionCh. 2 - Acids and Bases: Central to Understanding Organic ChemistryProblem 45cChapter 3, Problem 45c
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?
Verified step by step guidance1
Step 1: Recall the Henderson-Hasselbalch equation, which relates pH, pKa, and the ratio of the concentrations of the basic form ([A⁻]) and acidic form ([HA]) of a compound: .
Step 2: Identify the given values in the problem. The pKa of the compound is 4.6, and the ratio of the basic form ([A⁻]) to the acidic form ([HA]) is 10:1. This means .
Step 3: Substitute the ratio into the Henderson-Hasselbalch equation. Replace with , since the ratio is 10:1.
Step 4: Recall that equals 1. Substitute this value into the equation: .
Step 5: Add the pKa value (4.6) to 1 to determine the pH at which the concentration of the basic form is 10 times greater than the acidic form. The final pH can be calculated using this equation.
Verified video answer for a similar problem:
This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
2mWas this helpful?
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
pKa and pH Relationship
The pKa value of a compound indicates the pH at which half of the compound is in its acidic form and half is in its basic form. A lower pKa means a stronger acid. The relationship between pKa and pH is crucial for understanding the ionization of weak acids and bases in solution.
Recommended video:
Guided course
07:45
Identifying pKa values
Henderson-Hasselbalch Equation
The Henderson-Hasselbalch equation relates pH, pKa, and the ratio of the concentrations of the basic and acidic forms of a compound. It is expressed as pH = pKa + log([A-]/[HA]), where [A-] is the concentration of the base and [HA] is the concentration of the acid. This equation is essential for calculating the pH at which specific ratios of acid and base exist.
Recommended video:
Guided course
05:02Breaking down the different terms of the Gibbs Free Energy equation.
Concentration Ratios
Understanding concentration ratios is vital for solving the problem. If the concentration of the basic form is 10 times greater than that of the acidic form, this translates to a ratio of [A-]/[HA] = 10. This ratio can be plugged into the Henderson-Hasselbalch equation to find the corresponding pH.
Recommended video:
Guided course
04:21How to calculate enantiomeric excess.
Related Practice
Textbook Question
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)
946
views
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.
d. Draw the structure of alanine in a solution at pH = 12.
1021
views
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)?
768
views
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?
671
views
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)
840
views