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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7:36 minutes

Problem 24b

Textbook Question

Rank the following from strongest base to weakest base:
b.

Verified step by step guidance

Step 1: Understand the concept of basicity. Basicity refers to the ability of a species to donate a pair of electrons (act as a base). Stronger bases are more willing to donate electrons, while weaker bases are less willing.

Step 2: Analyze the conjugate acids of each base. The strength of a base is inversely related to the strength of its conjugate acid. For example, a weaker conjugate acid corresponds to a stronger base.

Step 3: Consider electronegativity. Fluoride ion (F⁻) is highly electronegative, meaning it holds onto its electrons tightly and is less willing to donate them, making it a weaker base compared to less electronegative species.

Step 4: Evaluate resonance and hybridization effects. CH₃C≡C⁻ (acetylide ion) has sp hybridization, which makes its lone pair more available for donation, increasing its basicity. CH₃CH₂O⁻ (ethoxide ion) and NH₂⁻ (amide ion) are also strong bases, but their basicity is influenced by factors like electronegativity and steric hindrance.

Step 5: Rank the bases from strongest to weakest based on the above considerations: CH₃C≡C⁻ > NH₂⁻ > CH₃CH₂O⁻ > F⁻. This ranking is based on the availability of the lone pair for donation and the stability of the conjugate acid.

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Key Concepts

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

Acidity and Basicity

Acidity and basicity are fundamental concepts in organic chemistry that describe the tendency of a substance to donate or accept protons (H+ ions). A strong base is a substance that readily accepts protons, while a weak base does so less readily. The strength of a base is often determined by its conjugate acid's stability; the weaker the conjugate acid, the stronger the base.

Conjugate Acid-Base Pairs

Conjugate acid-base pairs are related species that differ by the presence of a proton. When a base accepts a proton, it forms its conjugate acid. Understanding these pairs is crucial for ranking bases, as the stability of the conjugate acid influences the base's strength. A stable conjugate acid indicates a weaker base, while an unstable conjugate acid suggests a stronger base.

Electronegativity and Atomic Size

Electronegativity refers to the ability of an atom to attract electrons in a bond, while atomic size affects how easily a base can stabilize a negative charge. Generally, bases with less electronegative atoms or larger atomic size can better stabilize the negative charge when they accept protons, making them stronger bases. This concept is essential for comparing the basicity of different compounds.

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Related Practice

Textbook Question

For the bases shown, draw the conjugate acid and identify a pK_a value from Table 4.5 that would help you accurately estimate its stability.

(d)

Textbook Question

a. Which is a stronger base: CH₃COO⁻ or HCOO⁻? (The pK_a of CH₃COOH is 4.8; the pK_a of HCOOH is 3.8.)

b. Which is a stronger base: HO⁻ or ^-NH₂? (The pK_a of H2O is 15.7; the pK_a of NH3 is 36.)

c. Which is a stronger base: H₂O or CH₃OH? (The pK_a of H3O+ is −1.7; the pK_a of CH₃O⁺H₂ is −2.5.)

Textbook Question

A medicinal chemist needed to deprotonate acetylene ( HC≡CH ) for use in a coupling reaction. Among the options given, which base(s) could be used for this process?

Textbook Question

For each compound, indicate the atom that is most apt to be protonated.

Textbook Question

Citrus fruits are rich in citric acid, a compound with three COOH groups. Explain the following:

b. The third pK_a is greater than the pKa of acetic acid.

Textbook Question

Given the structure of ascorbic acid (vitamin C):

(a) Is ascorbic acid a carboxylic acid?

(b) Compare the acid strength of ascorbic acid (pK_a = 4.71) with acetic acid.

Textbook Question

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

Textbook Question