Buffer Capacity Calculator

Buffer capacity (β) measures how resistant a buffer is to pH change. It is defined as the number of moles of strong acid or base needed to change 1 liter of buffer by 1 pH unit.

Formula (Van Slyke equation):

β = 2.303 × C × Ka × [H⁺] / (Ka + [H⁺])²

Where:

• C = total buffer concentration = [HA] + [A⁻] (mol/L)
• Ka = acid dissociation constant
• [H⁺] = hydrogen ion concentration = 10^(-pH)

Maximum buffer capacity: β is maximum when pH = pKa (when [HA] = [A⁻]). At maximum: β_max = 0.576 × C

Estimating amount of acid/base to add:

Moles of strong acid/base = β × ΔpH × Volume (L)

Effective buffer range: Buffers work well within pH = pKa ± 1. Outside this range, buffer capacity drops dramatically.

Common buffer systems:

Biological importance: Blood is buffered primarily by the bicarbonate/CO₂ system at pH 7.35–7.45. A pH drop below 7.35 (acidosis) or above 7.45 (alkalosis) is a medical emergency. The kidneys and lungs work together to maintain blood pH within this narrow range.

Operational definition. If you’d rather measure capacity than compute it from constants, the working definition is just β = ΔC_b / ΔpH: add a known amount of strong acid or base to a liter of buffer, measure how far the pH shifts, divide. The Van Slyke formula above is what falls out when you do this calculation analytically for a single-pKa buffer; the operational form is what a real bench measurement gives you.