How this calculation works
The Buffer Solution pH Calculator computes the equilibrium pH and buffer capacity of weak acid / conjugate base conjugate pairs using the Henderson-Hasselbalch equation.
Mathematical formula and logic
pH = pKa + log₁₀([Conjugate Base A⁻] / [Weak Acid HA]). Effective buffering range is pKa ± 1.0 pH units.
Worked example
An acetate buffer with pKa = 4.76 containing 0.15 M Sodium Acetate [A⁻] and 0.10 M Acetic Acid [HA] has a pH = 4.76 + log₁₀(0.15 / 0.10) = 4.76 + 0.176 = 4.94.
Calculation assumptions
- Henderson-Hasselbalch approximation valid when concentrations of [HA] and [A⁻] are at least 100x greater than Ka.
- Dilute aqueous buffer solutions at 25°C.
Frequently asked questions
What is a chemical buffer solution?
A buffer solution is an aqueous mixture of a weak acid and its conjugate base (or a weak base and conjugate acid) that resists changes in pH when small amounts of strong acid or base are added.
What is the optimal pH range for a buffer?
A buffer works most effectively within ±1.0 pH unit of its weak acid's pKa value, where the ratio of [A⁻]/[HA] remains between 1:10 and 10:1.
What happens when [A⁻] equals [HA] in a buffer?
When conjugate base and weak acid concentrations are equal ([A⁻] = [HA]), log₁₀(1) = 0, so the solution pH equals the pKa exactly, providing maximum bidirectional buffering capacity.
What is the physiological buffer system in human blood?
Human blood relies primarily on the carbonic acid / bicarbonate buffer system (H₂CO₃ / HCO₃⁻, pKa 6.1) combined with respiratory respiration to strictly maintain blood pH within 7.35 to 7.45.
What is buffer capacity?
Buffer capacity is a quantitative measure of a buffer's resistance to pH changes, which increases with higher absolute molar concentrations of the weak acid and conjugate base components.
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