Buffer pH Calculator
Calculate the pH of a buffer solution using the Henderson-Hasselbalch equation. Enter the pKa and concentrations of the weak acid and its conjugate base.
pKa of the weak acid (for acetic acid, pKa = 4.76)
Molarity of the weak acid in the buffer
Molarity of the conjugate base (e.g., sodium acetate)
What is the Henderson-Hasselbalch equation?
The Henderson-Hasselbalch equation is pH = pKa + log([A⁻]/[HA]), where pH is the buffer pH, pKa is the acid dissociation constant, [A⁻] is the conjugate base concentration, and [HA] is the weak acid concentration. It is the fundamental equation for calculating buffer pH.
When is buffer pH equal to pKa?
When the concentrations of weak acid [HA] and conjugate base [A⁻] are equal, the log term becomes log(1) = 0, so pH = pKa. This is when the buffer has its maximum buffering capacity.
What is the effective buffer range?
A buffer is generally effective within ±1 pH unit of the pKa. Outside this range, one component becomes too dilute to effectively neutralize added acid or base. For example, an acetate buffer (pKa = 4.76) works best between pH 3.76 and 5.76.
How do I prepare a buffer at a specific pH?
Use the Henderson-Hasselbalch equation to calculate the required ratio of [A⁻]/[HA]. For example, to make pH 5.0 with acetic acid (pKa 4.76): 5.0 = 4.76 + log([A⁻]/[HA]), so [A⁻]/[HA] = 10^0.24 ≈ 1.74. Mix acetate and acetic acid in this ratio.