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

1. 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.
2. 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.
3. 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.
4. 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.
5. 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.

Key Concepts

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.