Buffer Capacity Calculator

Calculate buffer capacity (beta) using beta = 2.303*C*Ka*[H+]/(Ka+[H+])^2. Find optimal buffer concentration and determine resistance to pH change for any buffer system.

🧪 Acid-Base📐 β = 2.303·C·Ka·[H⁺]/(Ka+[H⁺])²🧪 Chemistry

Total buffer concentration C (mol/L)

pH of buffer

pKa of weak acid

Please enter valid values.

Formula & Reference

Variable	Symbol	Formula	Units
Buffer Capacity Calculator	—	β = 2.303·C·Ka·[H⁺]/(Ka+[H⁺])²	mol/L per pH

Step-by-Step Examples

Example 1

Acetate Buffer at pKa

C=0.100 M acetate buffer at pH=pKa=4.74.

Maximum buffer capacity at pH = pKa
Beta_max = 2.303 x C/4 = 2.303 x 0.100/4 = 0.0576 mol/L-pH
50:50 ratio of acetic acid to acetate

✓ Beta = 0.0576 mol/L-pH (maximum capacity)

Example 2

Buffer Off-Peak

C=0.100 M, pKa=4.74, but pH=5.74 (1 unit from pKa).

At pH = pKa+1: ratio [A-]/[HA] = 10:1
Beta decreases as pH moves from pKa

✓ Buffer capacity reduced at pH 5.74

Example 3

Compare Concentrations

Same acetate buffer: 0.10 M vs 0.50 M at pKa.

Beta_max proportional to C
0.50 M: beta = 5x more than 0.10 M
More concentrated = more resistant to pH change

✓ Higher C = greater buffer capacity (5x here)

Real-World Applications

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Biological Buffers

PBS, HEPES, TRIS buffers maintain pH in cell culture and biochemical experiments.

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IV Fluids

Bicarbonate buffer (pKa=6.1) in blood. Capacity proportional to HCO3- concentration.

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Analytical Chemistry

HPLC mobile phases: buffer capacity prevents pH shifts that alter retention times.

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Pharmaceutical Formulation

Drug stability requires buffered pH. Buffer capacity determines how much pH changes per addition of drug.

Common Mistakes to Avoid

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Maximum capacity at pH = pKa

Buffer capacity is maximum when pH = pKa (equal amounts of acid and conjugate base).

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Capacity decreases rapidly beyond pKa +/- 1

At pH = pKa +/- 1: capacity falls to ~50% of maximum. Beyond pKa +/- 2: poor buffering.

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Capacity proportional to total concentration

Double the concentration: double the buffer capacity. Use more concentrated buffer when stronger resistance needed.

Frequently Asked Questions

What is buffer capacity? ▾

The moles of acid or base that must be added per liter to change pH by 1 unit. Higher beta: more resistant to pH change. Units: mol/(L-pH).

What determines optimal buffer? ▾

Choose acid with pKa within 0.5 pH of target. Use concentration as high as practical. Avoid large excess of either acid or conjugate base.

Why does buffer capacity decrease away from pKa? ▾

At extreme ratios (100:1 of acid to base), adding base quickly uses up all acid without much change in pH. Little resistance left.

What is the Van Slyke equation? ▾

Buffer capacity beta = 2.303 x Kw/[H+] + 2.303 x [H+] + 2.303 x C x Ka x [H+]/(Ka+[H+])^2. Includes water and excess acid/base contributions at extremes.

What buffers are used at physiological pH? ▾

pH 7.4 target: HEPES (pKa 7.5), MOPS (pKa 7.2), PIPES (pKa 6.8), PBS (phosphate pKa 7.2), bicarbonate/CO2 in blood (pKa 6.1 but respiratory controlled).

Related Chemistry Calculators

Formula Explorer connections

Interpretation: This relationship connects hydrogen-ion activity, dissociation, conjugate ratios or titration stoichiometry to acid–base behavior. Assumption: Concentration approximates activity mainly in dilute solutions. Temperature, ionic strength, acid strength and equilibrium approximations affect accuracy.

Buffer pH Calculator →Common Ion Effect Calculator →EDTA Complexometric Titration →Chemistry Formula Explorer →