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

Equilibrium Constant

Organic Chemistry

3. Acids and Bases

Equilibrium Constant

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4:55 minutes

Problem 60a

Textbook Question

For each of the following compounds, draw the form that predominates at pH = 3, pH = 6, pH = 10, and pH = 14:
a. CH₃COOH (pK_a= 4.8)

Verified step by step guidance

Step 1: Understand the relationship between pH and pKa. The Henderson-Hasselbalch equation, \( \text{pH} = \text{pKa} + \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right) \), helps determine the ratio of the deprotonated form \( [\text{A}^-] \) to the protonated form \( [\text{HA}] \). When \( \text{pH} < \text{pKa} \), the protonated form \( [\text{HA}] \) predominates, and when \( \text{pH} > \text{pKa} \), the deprotonated form \( [\text{A}^-] \) predominates.

Step 2: Analyze the compound CH3COOH (acetic acid). Acetic acid is a weak acid with a \( \text{pKa} = 4.8 \). The protonated form is \( \text{CH}_3\text{COOH} \), and the deprotonated form is \( \text{CH}_3\text{COO}^- \).

Step 3: Determine the predominant form at \( \text{pH} = 3 \). Since \( \text{pH} = 3 \) is less than \( \text{pKa} = 4.8 \), the protonated form \( \text{CH}_3\text{COOH} \) will predominate.

Step 4: Determine the predominant form at \( \text{pH} = 6 \). Since \( \text{pH} = 6 \) is greater than \( \text{pKa} = 4.8 \), the deprotonated form \( \text{CH}_3\text{COO}^- \) will predominate.

Step 5: Determine the predominant forms at \( \text{pH} = 10 \) and \( \text{pH} = 14 \). Both \( \text{pH} = 10 \) and \( \text{pH} = 14 \) are much greater than \( \text{pKa} = 4.8 \), so the deprotonated form \( \text{CH}_3\text{COO}^- \) will predominate in both cases.

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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 protonated (acid) and deprotonated (base) forms of a compound in solution. The pKa value indicates the pH at which half of the acid is dissociated. Understanding this equilibrium is crucial for predicting the predominant form of a compound at different pH levels.

pH Scale

The pH scale measures the acidity or basicity of a solution, ranging from 0 (very acidic) to 14 (very basic), with 7 being neutral. The pH affects the ionization of acids and bases, influencing their chemical behavior. Knowing the pH of a solution helps determine whether a compound exists primarily in its protonated or deprotonated form.

Dissociation of Acids

Dissociation of acids involves the release of protons (H+) when an acid is dissolved in water. For weak acids like acetic acid (CH3COOH), the extent of dissociation is influenced by the pH of the solution. At pH values below the pKa, the acid predominates, while at pH values above the pKa, the conjugate base becomes more prevalent.

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Related Practice

Textbook Question

For each of the following compounds (here shown in their acidic forms), write the form that predominates in a solution with a pH = 5.5:

g. HNO₂ (pK_a= 3.4)

h. HNO₃ (pK_a= −1.3)

Textbook Question

As long as the pH is not less than ___________, at least 50% of a protonated amine with a pK_a value of 10.4 will be in its neutral, nonprotonated form.

Textbook Question

Indicate whether a protonated amine (RN⁺H₃) with a pKa value of 9 has more charged or more neutral molecules in a solution with the pH values given in Problem 41.

1. pH = 1

2. pH = 3

3. pH = 5

4. pH = 7

5. pH = 10

6. pH = 13

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 (pK_a= 4.9)

2. CH₃N⁺H₃ (pK_a= 10.7)

Textbook Question

For each of the following compounds (here shown in their acidic forms), write the form that predominates in a solution with a pH = 5.5:

e. ⁺NH4 (pK_a= 9.4)

f. HC≡N (pK_a= 9.1)

Textbook Question

Indicate whether an alcohol (ROH) with a pK_a value of 15 has more charged or more neutral molecules in a solution with the pH values given in Problem 41.

1. pH = 1

2. pH = 3

3. pH = 5

Textbook Question

Indicate whether an alcohol (ROH) with a pK_a value of 15 has more charged or more neutral molecules in a solution with the pH values given in Problem 41.

3. pH = 7

4. pH = 10

5. pH = 13

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 pK_a values of the two groups are shown.

d. Draw the structure of alanine in a solution at pH = 12.

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For each of the following compounds, draw the form that predominates at pH = 3, pH = 6, pH = 10, and pH = 14:a. CH3COOH (pKa = 4.8)

Key Concepts

Acid-Base Equilibrium

pH Scale

Dissociation of Acids

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For each of the following compounds, draw the form that predominates at pH = 3, pH = 6, pH = 10, and pH = 14:
a. CH₃COOH (pK_a= 4.8)