Buffer Capacity Calculator

A buffer solution resists changes in pH when small amounts of acid or base are added — and buffer capacity (β) measures how well it does that job. Enter your buffer's pKa (or Ka), total buffer concentration, and target pH into the Buffer Capacity Calculator to get the Total Buffer Capacity (βtotal). Secondary outputs include the buffer's own contribution (βbuffer), water's contribution (βwater), and the individual [HA] and [A⁻] concentrations at your target pH.

Input Type *

For acetic acid/acetate buffer, pKa = 4.76

mol/L

Combined concentration of acid and conjugate base

pH at which to calculate buffer capacity

Recommended for extreme pH values

Apply appropriate significant figure rounding

Results

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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Frequently Asked Questions

What is buffer capacity?

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.

How do you calculate buffer capacity?

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.

When should I include the water contribution?

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.

What pH gives maximum buffer capacity?

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.

How does concentration affect buffer capacity?

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.

What's the difference between pKa and Ka?

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.

Can this calculator be used for polyprotic acids?

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.