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

Previous problemNext problem

Problem 30a

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)

Verified step by step guidance

Step 1: Recall the relationship between pKa and the ratio of acid to conjugate base. The Henderson-Hasselbalch equation is given as:

pH = pKa + \log (\frac{[A-]}{[HA]})

, where [HA] is the concentration of the acid and [A⁻] is the concentration of the conjugate base.

Step 2: Rearrange the Henderson-Hasselbalch equation to isolate the ratio of acid to conjugate base:

\frac{[HA]}{[A-]} = 10^{(pKa - pH)}

Step 3: Identify the pKa value from the problem. The pKa of the acid is given as 20.

Step 4: Determine the pH of the solution. If the pH is not explicitly provided, it must be assumed or calculated based on additional information. For example, if the solution is neutral, the pH is 7.

Step 5: Substitute the pKa and pH values into the rearranged equation to calculate the ratio of acid to conjugate base. This will yield the ratio

\frac{[HA]}{[A-]}

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above

Play a video:

Was this helpful?

Key Concepts

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

pKₐ and Acid-Base Equilibrium

pKₐ is a measure of the strength of an acid in solution, defined as the negative logarithm of the acid dissociation constant (Kₐ). A lower pKₐ value indicates a stronger acid, which dissociates more completely in solution. Understanding pKₐ is essential for calculating the ratio of acid to conjugate base, as it directly influences the equilibrium position of the acid-base reaction.

Henderson-Hasselbalch Equation

The Henderson-Hasselbalch equation relates the pH of a solution to the pKₐ of the acid and the ratio of the concentrations of the conjugate base and the acid. It is expressed as pH = pKₐ + log([A⁻]/[HA]). This equation is crucial for determining the ratio of acid to conjugate base, as it allows for the calculation of this ratio based on the known pH and pKₐ values.

Acid-Base Reaction Dynamics

Acid-base reactions involve the transfer of protons (H⁺) between species, leading to the formation of conjugate acids and bases. The dynamics of these reactions are influenced by factors such as concentration, temperature, and the presence of other ions in solution. Understanding these dynamics is important for accurately calculating the acid to conjugate base ratio, as it affects the equilibrium state of the reaction.

Watch next

Master Why we use pKa instead of pH. with a bite sized video explanation from Johnny

Start learning

Related Videos

Related Practice

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

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

(e)

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?

Textbook Question

At what pH does 80% of the acid exist in its acidic form?

Show more practices

Download the Mobile app

Privacy

Do not sell my personal information

Accessibility

Patent notice

Sitemap

Given that the indicated pKa values correspond to the acid dissociation reactions shown, calculate the ratio of acid to conjugate base for the reactions shown.(a)

Key Concepts

pKₐ and Acid-Base Equilibrium

Henderson-Hasselbalch Equation

Acid-Base Reaction Dynamics

Watch next

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)