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

Equilibrium Constant

Organic Chemistry

3. Acids and Bases

Equilibrium Constant

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3:32 minutes

Problem 62e(iv)

Textbook Question

For the following acid–base pairs, (iv) calculate K_eq;
(e)

Verified step by step guidance

Step 1: Identify the acid and base on both sides of the equilibrium. In the given reaction, the acid on the left side is acetic acid (CH3COOH), and the base is ethanol (CH3CH2OH). On the right side, the conjugate base of acetic acid is acetate ion (CH3COO⁻), and the conjugate acid of ethanol is ethoxide ion (CH3CH2O⁻).

Step 2: Determine the pKa values of the acids involved. The pKa of acetic acid is approximately 4.76, and the pKa of ethanol is approximately 16. This information is crucial for calculating the equilibrium constant (Keq).

Step 3: Use the relationship between pKa values and Keq. The equilibrium constant for an acid-base reaction can be calculated using the formula: Keq = 10^(pKa(conjugate acid) - pKa(acid)).

Step 4: Substitute the pKa values into the formula. In this case, the conjugate acid is ethanol (pKa = 16), and the acid is acetic acid (pKa = 4.76). The formula becomes: Keq = 10^(16 - 4.76).

Step 5: Interpret the result. The calculated Keq will indicate the position of equilibrium. If Keq > 1, the equilibrium favors the products (right side). If Keq < 1, the equilibrium favors the reactants (left side).

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Key Concepts

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

Acid-Base Equilibrium

Acid-base equilibrium refers to the state where the rates of the forward and reverse reactions of an acid and its conjugate base are equal. This equilibrium is characterized by the equilibrium constant (Keq), which quantifies the ratio of the concentrations of products to reactants at equilibrium. Understanding this concept is crucial for calculating Keq for given acid-base pairs.

Equilibrium Constant (Keq)

The equilibrium constant (Keq) is a numerical value that expresses the ratio of the concentrations of products to reactants at equilibrium for a reversible reaction. For acid-base reactions, Keq can be calculated using the concentrations of the acid and its conjugate base. A higher Keq value indicates a stronger tendency for the reaction to favor products, while a lower value suggests a preference for reactants.

Conjugate Acid-Base Pairs

Conjugate acid-base pairs consist of two species that differ by the presence or absence of a proton (H+). In any acid-base reaction, the acid donates a proton to form its conjugate base, while the base accepts a proton to form its conjugate acid. Recognizing these pairs is essential for understanding the dynamics of acid-base reactions and for calculating the equilibrium constant.

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Related Practice

Textbook Question

Write the K_eq expression for the following acid–base reactions. [You don't need to calculate K_eq here.]

(c)

Textbook Question

Parts (a)–(d) of this assessment assist in the development of what will become a common theme in organic reactions and should be worked in order. [Think carefully about how each question relates to the others.]

(c) Without worrying about the mechanism of the reaction, estimate an equilibrium constant for the following carbonyl addition reaction based on the relative stability of the Lewis bases.

Textbook Question

Calculate the equilibrium constant for the reaction of ethylamine and propanoic acid. Which side is favored?

Textbook Question

How do you know that a proton with a low pK_a value is acidic (besides 'I just remember')?

Textbook Question

Given that the indicated pK_a values correspond to the acid dissociation reactions shown, calculate the ratio of acid to conjugate base for the reactions shown.

(a)

Textbook Question

Using pK_a values, calculate an approximate K_eq value for the following substitution reaction.

Textbook Question

Amino acids exist predominantly in one of the following forms. Which is it? Explain your answer.

Textbook Question

At what pH is the concentration of a compound, with a pK_a = 4.6, 10 times greater in its basic form than in its acidic form?

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