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

Acid Base Equilibrium

Organic Chemistry

3. Acids and Bases

Acid Base Equilibrium

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3:32 minutes

Problem 47

Textbook Question

Do the equilibria of the following acid–base reactions lie to the right or the left? (The pK_a of H2O2 is 11.6.)
HOOH + HO⁻⇌ HOO⁻+ H2O
RC☰CH + HOO⁻⇌ RC☰C⁻+ HOOH

Verified step by step guidance

Step 1: Understand the problem. The question asks whether the equilibrium of each acid-base reaction lies to the right or the left. This depends on the relative acid strengths of the acids on both sides of the reaction, which can be determined using their pKa values. The equilibrium favors the side with the weaker acid (higher pKa).

Step 2: Analyze the first reaction: HOOH + HO⁻ ⇌ HOO⁻ + H₂O. Here, HOOH (hydrogen peroxide) is the acid on the left, and H₂O (water) is the acid on the right. The pKa of HOOH is given as 11.6, and the pKa of H₂O is 15.7. Compare these pKa values to determine which acid is weaker.

Step 3: Analyze the second reaction: RC≡CH + HOO⁻ ⇌ RC≡C⁻ + HOOH. Here, RC≡CH (a terminal alkyne) is the acid on the left, and HOOH (hydrogen peroxide) is the acid on the right. The pKa of a terminal alkyne is approximately 25, and the pKa of HOOH is 11.6. Compare these pKa values to determine which acid is weaker.

Step 4: Use the principle that equilibrium favors the side with the weaker acid (higher pKa). For each reaction, identify whether the equilibrium lies to the right or the left based on the relative pKa values of the acids on both sides.

Step 5: Summarize your findings for both reactions. For the first reaction, compare HOOH and H₂O. For the second reaction, compare RC≡CH and HOOH. State whether the equilibrium lies to the right or the left for each reaction based on the weaker acid.

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Key Concepts

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

Acid-Base Equilibria

Acid-base equilibria refer to the balance between acids and bases in a chemical reaction. The position of equilibrium indicates whether the reactants or products are favored. In general, the equilibrium will lie to the side of the weaker acid and base, which can be determined by comparing their pKa values.

pKa and Strength of Acids

The pKa value is a quantitative measure of the strength of an acid in solution; lower pKa values indicate stronger acids. In the context of acid-base reactions, knowing the pKa of the acids involved helps predict the direction of the equilibrium. For example, if the pKa of H2O2 is 11.6, it suggests that H2O2 is a relatively weak acid.

Reaction Mechanism and Stability

The stability of the resulting species in a reaction can influence the position of equilibrium. For instance, the stability of the conjugate base formed after deprotonation can determine whether the equilibrium favors the products or reactants. In the given reactions, analyzing the stability of the alkynyl anion and the hydroperoxide ion is crucial for predicting the direction of the equilibria.

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Related Practice

Textbook Question

Complete the following acid–base reactions. In each case, indicate whether the equilibrium favors the reactants or the products, and explain your reasoning.

(g) KOH + CH₃CH₂OH ⇌

Textbook Question

Complete the following acid–base reactions. In each case, indicate whether the equilibrium favors the reactants or the products, and explain your reasoning.

(f) (CH₃)₃C–O^– + H₂O ⇌

Textbook Question

Write equations for the following acid–base reactions. Label the conjugate acids and bases, and show any inductive stabilization. Predict whether the equilibrium favors the reactants or products. Try to do this without using a table of pK_a values, but if you need a hint, you can consult Appendix 4.

g. NaOCH₂CH₃ + Cl₂CHCH₂OH

h. H₂Se + NaNH₂

i. CH₃CHFCOOH + FCH₂CH₂COO^–

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:

c. H₃O⁺ (pK_a = −1.7)

d. HBr (pK_a = −9)

Textbook Question

Using pK_a values for the conjugate acids of the bases on each side of the reaction arrow, identify which side of the equilibrium would be favored in the following hypothetical reactions.

(a)

Textbook Question

For each of the following acid–base reactions, (i) predict which side of the reaction you expect to be favored. If a pK_a is not one of the ten common ones we learned in Chapter 4, it will be given to you.

(a)

Textbook Question

An acid has a K_a of 4.53 × 10⁻⁶ in water. What is its K_eq for reaction with water in a dilute solution? ([H₂O] = 55.5 M)

Textbook Question

For each of the following reactions, suggest which solvent(s) would be compatible with the acids and bases involved. (We will ignore any other possible reactions for now.) Your choices of solvents are pentane, diethyl ether, ethanol, water, and ammonia. Refer to Appendix 4 for any needed values of pK_a, or estimate them.

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Do the equilibria of the following acid–base reactions lie to the right or the left? (The pKa of H2O2 is 11.6.)HOOH + HO− ⇌ HOO− + H2ORC☰CH + HOO− ⇌ RC☰C− + HOOH

Key Concepts

Acid-Base Equilibria

pKa and Strength of Acids

Reaction Mechanism and Stability

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Do the equilibria of the following acid–base reactions lie to the right or the left? (The pK_a of H2O2 is 11.6.)
HOOH + HO⁻⇌ HOO⁻+ H2O
RC☰CH + HOO⁻⇌ RC☰C⁻+ HOOH