Buffer Capacity Explorer (β vs pH)

Buffer capacity β measures how much strong acid or base a buffer can absorb per unit change in pH. Slide the controls below and watch where β peaks: a buffer is strongest exactly at pH = pKa, scales up with concentration, and fades to roughly a third of its peak just one pH unit to either side. That is why buffers are only recommended within pKa ± 1.

Controls

Buffer pKa where capacity peaks

7.2

Total concentration C (mol·L⁻¹) [HA] + [A⁻]

0.10

Include water self-buffering term adds 2.303·([H⁺]+[OH⁻]) — only matters at very low / high pH

Overlay a second buffer mix two buffers to widen the usable range

Peak capacity at pH = pKa

—

β_max ≈ 0.576 · C

At the edge of the useful range, capacity has dropped to about — of its peak.

Buffer 1 (β₁)

This model is simplified for teaching: activity ≈ concentration (ionic strength is ignored) and polyprotic buffers are represented by a single relevant pKa. Real buffer capacity can differ, so verify values for actual lab work.