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

pKa

Organic Chemistry

3. Acids and Bases

pKa

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6:08 minutes

Problem 69

Textbook Question

You are planning to carry out a reaction that produces protons. The reaction will be buffered at pH = 10.5. Would it be better to use a protonated methylamine/methylamine buffer or a protonated ethylamine/ethylamine buffer? (pK_a of protonated methylamine = 10.7; pK_a of protonated ethylamine = 11.0)

Verified step by step guidance

Step 1: Understand the concept of buffering capacity. A buffer works best when the pH of the solution is close to the pKa of the conjugate acid in the buffer system. This is because the buffer can effectively resist changes in pH when the concentrations of the weak acid and its conjugate base are similar.

Step 2: Compare the pKa values of the two buffer systems provided. The pKa of protonated methylamine is 10.7, and the pKa of protonated ethylamine is 11.0. The closer the pKa is to the desired pH (10.5), the better the buffer system will perform.

Step 3: Calculate the difference between the pH and the pKa for each buffer system. For the protonated methylamine/methylamine buffer, the difference is |10.5 - 10.7| = 0.2. For the protonated ethylamine/ethylamine buffer, the difference is |10.5 - 11.0| = 0.5.

Step 4: Based on the calculations, the protonated methylamine/methylamine buffer has a smaller difference between its pKa and the desired pH, meaning it is closer to the optimal buffering range.

Step 5: Conclude that the protonated methylamine/methylamine buffer would be a better choice for buffering at pH 10.5, as it is more effective at maintaining the desired pH due to its pKa being closer to the target pH.

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Key Concepts

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

Buffer Solutions

Buffer solutions are mixtures that resist changes in pH upon the addition of small amounts of acids or bases. They typically consist of a weak acid and its conjugate base or a weak base and its conjugate acid. In this case, the choice between methylamine and ethylamine buffers is crucial for maintaining the desired pH during the reaction.

pKa and Acid-Base Equilibrium

The pKa value is a measure of the strength of an acid in solution; it indicates the pH at which half of the acid is dissociated. A lower pKa value means a stronger acid. In this scenario, the pKa values of the protonated forms of methylamine and ethylamine help determine which buffer will be more effective at pH 10.5, as the buffer should ideally have a pKa close to the target pH.

Protonation and Deprotonation

Protonation refers to the addition of a proton (H+) to a molecule, while deprotonation is the removal of a proton. The balance between these processes is essential in buffer systems, as they determine the concentration of protonated and deprotonated species. In this question, understanding how methylamine and ethylamine behave at the specified pH will influence the choice of buffer for effective proton management.

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You are planning to carry out a reaction that produces protons. The reaction will be buffered at pH = 10.5. Would it be better to use a protonated methylamine/methylamine buffer or a protonated ethylamine/ethylamine buffer? (pKa of protonated methylamine = 10.7; pKa of protonated ethylamine = 11.0)

Key Concepts

Buffer Solutions

pKa and Acid-Base Equilibrium

Protonation and Deprotonation

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