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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5:54 minutes

Problem 17a

Textbook Question

Ethyne (HC≡CH) has a pK_a value of 25, water has a pK_a value of 15.7, and ammonia (NH3) has a pKa value of 36. Draw the equation, showing equilibrium arrows that indicate whether reactants or products are favored, for the acid–base reaction of ethyne with
a. HO^-.

Verified step by step guidance

Step 1: Identify the acid and base in the reaction. Ethyne (HC≡CH) acts as the acid because it donates a proton, and hydroxide ion (HO⁻) acts as the base because it accepts a proton.

Step 2: Write the acid-base reaction. Ethyne reacts with hydroxide ion to form its conjugate base, acetylide ion (HC≡C⁻), and water (H₂O), which is the conjugate acid of hydroxide. The reaction can be written as: HC≡CH + HO⁻ ⇌ HC≡C⁻ + H₂O.

Step 3: Compare the pKa values of the acid and conjugate acid. Ethyne has a pKa of 25, and water has a pKa of 15.7. Since water has a lower pKa, it is a stronger acid than ethyne.

Step 4: Determine the direction of equilibrium. The equilibrium will favor the formation of the weaker acid and weaker base. Since ethyne is a weaker acid than water, the equilibrium will favor the reactants (HC≡CH and HO⁻).

Step 5: Draw the equilibrium arrows. Use equilibrium arrows to indicate that the reaction favors the reactants. The longer arrow should point toward the reactants (HC≡CH and HO⁻), and the shorter arrow should point toward the products (HC≡C⁻ and H₂O).

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Key Concepts

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

Acid-Base Reactions

Acid-base reactions involve the transfer of protons (H+) between reactants. In this context, an acid donates a proton while a base accepts it. Understanding the strength of acids and bases, indicated by their pKa values, is crucial for predicting the direction of the equilibrium in these reactions.

pKa and Acid Strength

The pKa value is a quantitative measure of the strength of an acid in solution; lower pKa values indicate stronger acids. In the given question, ethyne (pKa 25) is a weaker acid compared to water (pKa 15.7), which means it is less likely to donate a proton. This concept is essential for determining which side of the reaction is favored.

Equilibrium in Chemical Reactions

Chemical equilibrium occurs when the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products. The position of equilibrium can be influenced by the relative strengths of the acids and bases involved, which is critical for drawing the correct equilibrium arrows in the reaction between ethyne and hydroxide ion (HO−).

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Related Practice

Textbook Question

For the following acid–base pairs, (iii) predict the favored side of equilibrium;

(e)

Textbook Question

Ethyne (HC≡CH) has a pK_a value of 25, water has a pK_a value of 15.7, and ammonia (NH₃) has a pK_a value of 36. Draw the equation, showing equilibrium arrows that indicate whether reactants or products are favored, for the acid–base reaction of ethyne with

b. ⁻NH₂.

c. Which would be a better base to use if you wanted to remove a proton from ethyne, HO⁻ or ^-NH₂?

Textbook Question

For each of the acid–base reactions in [Section 2.3], compare the pK_a values of the acids on either side of the equilibrium arrows to prove that the equilibrium lies in the direction indicated.

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Textbook Question

For each of the acid–base reactions in [Section 2.3], compare the pK_avalues of the acids on either side of the equilibrium arrows to prove that the equilibrium lies in the direction indicated.

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Textbook Question

Given the data in Problem 47:

a. What pH would you make the water layer to cause the carboxylic acid to dissolve in the water layer and the amine to dissolve in the ether layer?

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 pKa values, but if you need a hint, you can consult Appendix 4.

j. CF₃CH₂O^– + FCH₂CH₂OH

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 ⇌

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Ethyne (HC≡CH) has a pKa value of 25, water has a pKa value of 15.7, and ammonia (NH3) has a pKa value of 36. Draw the equation, showing equilibrium arrows that indicate whether reactants or products are favored, for the acid–base reaction of ethyne witha. HO-.

Key Concepts

Acid-Base Reactions

pKa and Acid Strength

Equilibrium in Chemical Reactions

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Ethyne (HC≡CH) has a pK_a value of 25, water has a pK_a value of 15.7, and ammonia (NH3) has a pKa value of 36. Draw the equation, showing equilibrium arrows that indicate whether reactants or products are favored, for the acid–base reaction of ethyne with
a. HO^-.