Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

3. Acids and Bases

Acid Base Equilibrium

Organic Chemistry

3. Acids and Bases

Acid Base Equilibrium

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3:14 minutes

Problem 46b

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 (pK_a= 4.9)
2. CH₃N⁺H₃ (pK_a= 10.7)

Verified step by step guidance

Step 1: Understand the problem. The question asks for the pH at which more than 99% of the compound is in a charged form. This involves determining whether the compound is protonated or deprotonated based on its pKa value and the pH of the solution.

Step 2: Recall the Henderson-Hasselbalch equation:

pH = pKa + \log^{(} \frac{[A^-]}{[HA]})

. This equation relates the pH, pKa, and the ratio of the concentrations of the deprotonated form ([A⁻]) to the protonated form ([HA]).

Step 3: For more than 99% of the compound to be in the charged form, the ratio of [A⁻] to [HA] (or vice versa, depending on the compound) must be at least 99:1. This corresponds to a difference of 2 in the logarithmic scale (log(99) ≈ 2).

Step 4: For CH3CH2COOH (pKa = 4.9), the charged form is CH3CH2COO⁻. To achieve 99% deprotonation, the pH must be at least 2 units higher than the pKa. Use the relationship:

pH = pKa + 2

. Substitute the pKa value to find the pH.

Step 5: For CH3N⁺H3 (pKa = 10.7), the charged form is CH3N⁺H3. To achieve 99% protonation, the pH must be at least 2 units lower than the pKa. Use the relationship:

pH = pKa - 2

. Substitute the pKa value to find the pH.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Acid-Base Equilibrium

Acid-base equilibrium refers to the balance between the concentrations of acids and their conjugate bases in a solution. The pKa value indicates the strength of an acid; lower pKa values correspond to stronger acids. Understanding this equilibrium is crucial for predicting the protonation state of compounds at different pH levels.

pH and Charge

pH is a measure of the hydrogen ion concentration in a solution, influencing the protonation state of acidic and basic functional groups. For a compound to be more than 99% charged, the pH must be significantly lower than the pKa for acids or higher than the pKa for bases. This relationship helps determine the predominant form of a compound in solution.

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]). This equation is essential for calculating the pH at which a specific percentage of a compound exists in its charged form, aiding in the analysis of the compounds in the question.

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Related Practice

Textbook Question

Using pK_a values for the conjugate acids of the bases on each side of the reaction arrow, identify which side of the equilibrium would be favored in the following hypothetical reactions.

(a)

Textbook Question

For each of the following acid–base reactions, (i) predict which side of the reaction you expect to be favored. If a pK_a is not one of the ten common ones we learned in Chapter 4, it will be given to you.

(a)

Textbook Question

An acid has a K_a of 4.53 × 10⁻⁶ in water. What is its K_eq for reaction with water in a dilute solution? ([H₂O] = 55.5 M)

Textbook Question

For each of the following reactions, suggest which solvent(s) would be compatible with the acids and bases involved. (We will ignore any other possible reactions for now.) Your choices of solvents are pentane, diethyl ether, ethanol, water, and ammonia. Refer to Appendix 4 for any needed values of pK_a, or estimate them.

Multiple Choice

In the context of acid-base equilibrium, which of the following factors can disrupt the Hardy-Weinberg equilibrium?

Multiple Choice

Which of the following statements best explains why scientists study acid-base equilibrium in organic chemistry?

Multiple Choice

Which of the following statements is true regarding the effect of enzyme phosphorylation on acid-base equilibrium?

Multiple Choice

Which of the following conditions is required for maintaining acid-base equilibrium in a solution?

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