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

Ranking Acidity

Organic Chemistry

3. Acids and Bases

Ranking Acidity

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Problem 36b

Textbook Question

Using qualitative reasoning for the acid–base reactions shown,
(i) which is stronger, the acid or the conjugate acid?
(ii) Which side of the reaction is favored?
(iii) Would you expect a K_eqgreater than, equal to, or less than 1?
(b)

Verified step by step guidance

Step 1: Identify the acid and conjugate acid in the reaction. In the given reaction, CH₄ is labeled as the acid, and NH₃ is labeled as the conjugate acid. The acid donates a proton, while the conjugate acid is the product formed after the base accepts a proton.

Step 2: Compare the relative acid strengths of CH₄ and NH₃. Methane (CH₄) is a very weak acid because its C-H bond is highly stable and does not readily donate a proton. Ammonia (NH₃), on the other hand, is a stronger acid compared to CH₄, as it can donate a proton more readily.

Step 3: Determine which side of the reaction is favored. Since CH₄ is a weaker acid and NH₃ is a stronger acid, the equilibrium will favor the side with the weaker acid and weaker base. Therefore, the reaction is likely to favor the reactants (CH₄ and NH₂⁻).

Step 4: Analyze the equilibrium constant qualitatively. The equilibrium constant (K_eq) for this reaction would be less than 1 because the reactants are favored over the products due to the relative weakness of CH₄ as an acid.

Step 5: Summarize the reasoning. The acid (CH₄) is weaker than the conjugate acid (NH₃), the reaction favors the reactants, and the equilibrium constant is expected to be less than 1.

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Key Concepts

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

Acid-Base Theory

Acid-base theory explains the behavior of acids and bases in chemical reactions. According to the Brønsted-Lowry theory, an acid is a proton donor, while a base is a proton acceptor. In the given reaction, CH4 acts as an acid by donating a proton to the base NH2-, forming its conjugate base CH3- and the conjugate acid NH3.

Conjugate Acid-Base Pairs

Conjugate acid-base pairs consist of two species that differ by the presence of a proton. When an acid donates a proton, it forms its conjugate base, while the base that accepts the proton forms its conjugate acid. Understanding these pairs is crucial for predicting the direction of acid-base reactions and determining which species is stronger in a given context.

Equilibrium and Reaction Favorability

In acid-base reactions, the position of equilibrium indicates which side of the reaction is favored. The stronger acid will donate a proton to the stronger base, leading to the formation of the weaker acid and base. The equilibrium constant (K) can be used to quantify this favorability, where a value greater than 1 suggests that the products are favored, while a value less than 1 indicates that the reactants are favored.

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Related Practice

Textbook Question

Which is the most stable base in each pair?

(b) HS^– and HO^–

Textbook Question

Identify the stronger base in each pair. Explain your choice. Citing pK_a values is not an acceptable answer.

(d)

Textbook Question

Imidazole is a heteroaromatic base. Which nitrogen, a or b, is most basic?

Textbook Question

Without using pK_a values, pick out the least reactive (most stable) base in each pair. Explain your answer.

(b)

Textbook Question

Identify the most stable conjugate base in each pair. Tell which structural features you analyzed and why you weighted them as you did in picking one answer.

(a)

Textbook Question

Identify the most stable conjugate base in each pair. Tell which structural features you analyzed and why you weighted them as you did in picking one answer.

(f)

Textbook Question

Identify the most acidic proton in each pair. Tell which structural features you analyzed and why you weighted them as you did in picking one answer. [Always start by drawing the conjugate base.]

(b)

Textbook Question

Identify the most acidic proton in each pair. Tell which structural features you analyzed and why you weighted them as you did in picking one answer. [Always start by drawing the conjugate base.]

(d)

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Using qualitative reasoning for the acid–base reactions shown,(i) which is stronger, the acid or the conjugate acid?(ii) Which side of the reaction is favored?(iii) Would you expect a Keq greater than, equal to, or less than 1?(b)

Key Concepts

Acid-Base Theory

Conjugate Acid-Base Pairs

Equilibrium and Reaction Favorability

Watch next

Using qualitative reasoning for the acid–base reactions shown,
(i) which is stronger, the acid or the conjugate acid?
(ii) Which side of the reaction is favored?
(iii) Would you expect a K_eqgreater than, equal to, or less than 1?
(b)