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

Previous problemNext problem

Struggling with Organic Chemistry?

Join thousands of students who trust us to help them ace their exams!Watch the first video

Multiple Choice

Rank the following molecules in order of increasing pK_a(lowest pK_a/most acidic to highest pK_a/least acidic).

I < II < III

II < III < I

II < I < III

III < I < II

Previous problemNext problem

Verified step by step guidance

Identify the functional groups present in each molecule. All three molecules are benzoic acid derivatives with different substituents on the benzene ring.

Consider the effect of substituents on acidity. Electron-withdrawing groups (EWGs) increase acidity by stabilizing the negative charge on the conjugate base, while electron-donating groups (EDGs) decrease acidity.

Analyze molecule II, which has a nitro group (NO2) as a substituent. The nitro group is a strong electron-withdrawing group, which will increase the acidity of the carboxylic acid.

Examine molecule III, which has a methoxy group (OCH3) as a substituent. The methoxy group is an electron-donating group, which will decrease the acidity of the carboxylic acid.

Compare molecule I, which has no additional substituents, to molecules II and III. Molecule I is less acidic than II due to the lack of an EWG, but more acidic than III due to the absence of an EDG. Therefore, the order of increasing pKa is II < I < III.