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

pKa

Organic Chemistry

3. Acids and Bases

pKa

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4:37 minutes

Problem 18

Textbook Question

Which is a stronger base: ethoxide ion or acetate ion? Give pK_b values (without looking them up) to support your choice.

Verified step by step guidance

Identify the conjugate acids of the given bases: Ethoxide ion (C₂H₅O⁻) is the conjugate base of ethanol (C₂H₅OH), and acetate ion (CH₃COO⁻) is the conjugate base of acetic acid (CH₃COOH).

Recall that the strength of a base is inversely related to the strength of its conjugate acid. A weaker conjugate acid corresponds to a stronger base.

Consider the acidity of the conjugate acids: Ethanol is a weaker acid compared to acetic acid. This is because ethanol lacks the resonance stabilization that acetic acid has, which makes acetic acid a stronger acid.

Since ethanol is a weaker acid, its conjugate base, the ethoxide ion, is a stronger base compared to the acetate ion.

Estimate the pKb values: Since ethoxide ion is a stronger base, it will have a lower pKb value compared to the acetate ion. The exact pKb values are not needed, but this reasoning supports the conclusion that ethoxide ion is the stronger base.

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Key Concepts

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

Acid-Base Strength

The strength of a base is determined by its ability to accept protons. A stronger base has a higher tendency to accept protons, which is often reflected in its pKb value. The lower the pKb, the stronger the base. Understanding this concept helps compare the basicity of ethoxide and acetate ions.

Resonance Stabilization

Resonance stabilization occurs when a molecule can delocalize electrons across multiple atoms, reducing its reactivity. Acetate ion is resonance-stabilized, making it less reactive and a weaker base compared to ethoxide ion, which lacks such stabilization. This concept is crucial for understanding why ethoxide is a stronger base.

Inductive Effect

The inductive effect involves the transmission of charge through a chain of atoms in a molecule, affecting its acidity or basicity. In ethoxide ion, the electron-donating effect of the ethyl group increases electron density on the oxygen, enhancing its basicity. This concept helps explain the relative strength of ethoxide as a base compared to acetate.