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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2:36 minutes

Problem 45c

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?

Verified step by step guidance

Step 1: Recall the Henderson-Hasselbalch equation, which relates pH, pKa, and the ratio of the concentrations of the basic form ([A⁻]) and acidic form ([HA]) of a compound:

pH = pKa + \log (\frac{[A ⁻}{[HA]})

Step 2: Identify the given values in the problem. The pKa of the compound is 4.6, and the ratio of the basic form ([A⁻]) to the acidic form ([HA]) is 10:1. This means

[A ⁻ = 10 \times [HA]

Step 3: Substitute the ratio into the Henderson-Hasselbalch equation. Replace

\log (\frac{[A ⁻}{[HA]})

with

\log (10)

, since the ratio is 10:1.

Step 4: Recall that

\log (10)

equals 1. Substitute this value into the equation:

pH = pKa + 1

Step 5: Add the pKa value (4.6) to 1 to determine the pH at which the concentration of the basic form is 10 times greater than the acidic form. The final pH can be calculated using this equation.

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Key Concepts

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

pKa and pH Relationship

The pKa value of a compound indicates the pH at which half of the compound is in its acidic form and half is in its basic form. A lower pKa means a stronger acid. The relationship between pKa and pH is crucial for understanding the ionization of weak acids and bases in solution.

Henderson-Hasselbalch Equation

The Henderson-Hasselbalch equation relates pH, pKa, and the ratio of the concentrations of the basic and acidic forms of a compound. It is expressed as pH = pKa + log([A-]/[HA]), where [A-] is the concentration of the base and [HA] is the concentration of the acid. This equation is essential for calculating the pH at which specific ratios of acid and base exist.

Concentration Ratios

Understanding concentration ratios is vital for solving the problem. If the concentration of the basic form is 10 times greater than that of the acidic form, this translates to a ratio of [A-]/[HA] = 10. This ratio can be plugged into the Henderson-Hasselbalch equation to find the corresponding pH.

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Related Practice

Textbook Question

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

(e)

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

Textbook Question

The pK_a of a protonated alcohol is about -2.5, and the pK_a of an alcohol is about 15. Therefore, as long as the pH of the solution is greater than _______ and less than _______, more than 50% of 2-propanol (the product of the reaction on p. 244) will be in its neutral, nonprotonated form.

Textbook Question

The pK_a of protonated acetone is about –7.5 and the pK_a of protonated hydroxylamine is 6.0.

a. In a reaction with hydroxylamine at pH 4.5 (Figure 16.2), what fraction of acetone is present in its acidic, protonated form?

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Textbook Question

The pK_a of acetic acid in water is 4.76. What effect will a decrease in the polarity of the solvent have on the pK_a? Why?

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

Key Concepts

pKa and pH Relationship

Henderson-Hasselbalch Equation

Concentration Ratios

Watch next

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?