AAMC FL Practice Exam

What does deprotonation involve?

1. The removal of a proton when pH is greater than pKa

2. The addition of a proton when pH is less than pKa

3. The transfer of a proton between molecules

4. The formation of a conjugate acid

The correct answer is: The removal of a proton when pH is greater than pKa

Deprotonation involves the removal of a proton (H⁺ ion) from a molecule. This process typically occurs when the pH of the solution is greater than the pKa of the acid. The pKa is a measure of the strength of an acid; it indicates the pH at which half of the acid is deprotonated. When the pH exceeds the pKa, the environment favors the deprotonation of the acid since there is a lower concentration of protons available compared to when the pH is lower. As such, the molecule is more likely to lose a proton, leading to the formation of its conjugate base. In the context of the other options, while the addition of a proton when pH is less than pKa denotes protonation rather than deprotonation, the transfer of a proton between molecules can happen during acid-base reactions but does not specifically define deprotonation itself. Lastly, the formation of a conjugate acid relates to the addition of a proton and is not relevant to the deprotonation process. Understanding this concept is crucial in acid-base chemistry, especially in determining the behavior of substances in different pH environments.