Final answer:
The answer is that as pH increases, the charge on molecules becomes more negative, and as pH decreases, the charge becomes more positive. The ideal buffer range is within half the pKa value. Therefore, correct option is d.
Step-by-step explanation:
The question pertains to the relationship between pH changes and the charge on molecules, as well as the ideal buffer range in relation to a substance's pKa value.
The correct answer to the question is as follows: As pH goes up, charge becomes more negative; As pH goes down, charge becomes more positive; with the ideal buffer range within half the pKa value.
This is because as the pH increases, there are fewer hydrogen ions (H+) in solution, which corresponds to an increase in the [base]/[acid] ratio, resulting in a more negative charge. Conversely, as the pH decreases (more H+ ions), the charge becomes more positive.
The optimum buffering capacity occurs when the pH is within one pH unit above or below the pKa, which reinforces the idea that the ideal buffer range is within half the pKa value.