Define buffer capacity.

Define buffer capacity.

• A. The amount of buffer solution present
• B. The pH of the buffer solution
• C. The ratio of conjugate base to acid
• D. The amount of strong acid or base that can be added to a buffer before the pH changes significantly

Answer: (D)

Buffer capacity is about how much strong acid or base a buffered solution can neutralize before its pH changes noticeably. It’s not about how much buffer you have by volume or just the current pH; it’s about the amount of additional H+ or OH− the system can absorb while keeping the pH from moving far. A practical way to think of it is the amount of strong acid or base needed to shift the pH by about one unit per liter of solution. Capacity is higher when there are large amounts of both buffering species (the weak acid and its conjugate base) present, and it’s greatest near the pKa, where both forms exist in appreciable quantities to neutralize added protons or hydroxide ions. If the buffer is dominated by one form, there’s less of the reactive species available to counter added acid or base once the dominant form is used up, so the capacity is lower. The pH alone doesn’t determine capacity; two buffers at the same pH can have very different capacities depending on the total amounts of buffering species.

Buffer capacity is about how much strong acid or base a buffered solution can neutralize before its pH changes noticeably. It’s not about how much buffer you have by volume or just the current pH; it’s about the amount of additional H+ or OH− the system can absorb while keeping the pH from moving far. A practical way to think of it is the amount of strong acid or base needed to shift the pH by about one unit per liter of solution. Capacity is higher when there are large amounts of both buffering species (the weak acid and its conjugate base) present, and it’s greatest near the pKa, where both forms exist in appreciable quantities to neutralize added protons or hydroxide ions. If the buffer is dominated by one form, there’s less of the reactive species available to counter added acid or base once the dominant form is used up, so the capacity is lower. The pH alone doesn’t determine capacity; two buffers at the same pH can have very different capacities depending on the total amounts of buffering species.