Enter your pKa Value, Total Buffer Concentration, and Target pH into the Buffer Capacity Calculator to find your Total Buffer Capacity, plus a breakdown of Buffer Capacity, Water Contribution, and [HA]/[A⁻] concentrations in your solution.
Total Buffer Capacity (βtotal)
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Buffer Capacity (βbuffer)
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Water Contribution (βwater)
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[HA] Concentration
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[A⁻] Concentration
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Buffer capacity (β) is a measure of how well a buffer solution resists changes in pH when acids or bases are added. It's defined as the amount of strong acid or base needed to change the pH by one unit, expressed in mol·L⁻¹·pH⁻¹.
Buffer capacity is calculated using the Van Slyke equation: β = 2.303 × C × (Ka × [H⁺]) / (Ka + [H⁺])², where C is the total buffer concentration, Ka is the acid dissociation constant, and [H⁺] is the hydrogen ion concentration.
The water contribution (βwater) becomes significant at very low (< 3) or very high (> 11) pH values. For most biological and analytical buffers operating near neutral pH, the water contribution is negligible.
Maximum buffer capacity occurs when pH equals pKa of the buffer system. At this point, the concentrations of the weak acid and its conjugate base are equal, providing optimal resistance to pH change.
Buffer capacity is directly proportional to the total concentration of the buffer components. Doubling the concentration doubles the buffer capacity, making the solution more resistant to pH changes.
pKa is the negative logarithm of Ka (pKa = -log Ka). Ka is the acid dissociation constant, while pKa is more commonly used because it gives convenient positive numbers. For example, if Ka = 1.8×10⁻⁵, then pKa = 4.76.
This calculator is designed for monoprotic buffer systems (one ionizable proton). For polyprotic acids like phosphoric acid, you would need to consider each ionization step separately or use specialized polyprotic buffer equations.