Calculate buffer pH using the Henderson-Hasselbalch equation. Determine pH from pKa and concentration ratio, or solve for any variable. Includes buffer capacity and common buffer recipes.
The Henderson-Hasselbalch equation is the cornerstone of buffer chemistry. It relates the pH of a buffer solution to the pKa of the weak acid and the ratio of conjugate base to acid concentrations: pH = pKa + log([A⁻]/[HA]). This simple relationship makes it possible to design buffers at any desired pH.
Buffers resist pH changes when small amounts of acid or base are added. They work because the weak acid can neutralize added base, while the conjugate base neutralizes added acid. The buffering capacity is greatest when [A⁻] = [HA] (i.e., pH = pKa), and the effective buffer range is typically pKa ± 1.
This calculator solves the Henderson-Hasselbalch equation for any variable: pH, pKa, [A⁻], or [HA]. It calculates buffer capacity, shows how pH changes when strong acid or base is added, provides common buffer recipes for laboratory use, and visualizes the buffer region on a titration-like curve.
For best results, combine calculator output with direct observation and periodic check-ins with a veterinarian or qualified advisor. Small adjustments made early usually improve comfort, safety, and long-term outcomes more than large corrective changes made later.
Design buffer solutions for any desired pH, calculate buffer capacity, and understand how buffers respond to added acid or base. Essential for biochemistry, analytical chemistry, and laboratory work. This henderson-hasselbalch calculator helps you compare outcomes quickly and reduce avoidable mistakes when making day-to-day care decisions. Use the estimate as a planning baseline and confirm final decisions with a qualified professional when risk is high.
Henderson-Hasselbalch: pH = pKa + log₁₀([A⁻]/[HA]) Rearranged: [A⁻]/[HA] = 10^(pH - pKa) pKa = pH - log₁₀([A⁻]/[HA]) Buffer capacity β = 2.303 × C × Ka × [H⁺] / (Ka + [H⁺])² Effective range: pKa ± 1
Result: pH = 4.94
For an acetic acid / sodium acetate buffer with pKa = 4.76: pH = 4.76 + log(0.15/0.10) = 4.76 + log(1.5) = 4.76 + 0.176 = 4.94. The pH is slightly above pKa because the base form predominates.
Laboratory buffers are typically prepared at 20-200 mM total concentration. The choice of buffer depends on the target pH, compatibility with the experiment (some buffers chelate metals or interfere with assays), temperature stability, and ionic strength requirements. Good's buffers (HEPES, MES, MOPS, etc.) were specifically designed for biological research.
During the titration of a weak acid with a strong base, the buffer region spans the half-equivalence point. At half-equivalence, exactly half the acid is converted to its conjugate base, so [A⁻] = [HA] and pH = pKa. The Henderson-Hasselbalch equation describes the entire buffer region between 10% and 90% neutralization.
Polyprotic acids (H₃PO₄, H₂CO₃, citric acid) can buffer at multiple pH values — one for each ionization. Phosphate buffer works near pH 2.1, 7.2, and 12.4. This makes phosphate versatile but requires choosing the right conjugate pair for your target pH.
It's valid when (1) the acid is weak (pKa 2-12), (2) concentrations are >> Ka, and (3) the solution doesn't dilute too much. It breaks down for very dilute buffers, strong acids/bases, or polyprotic systems without simplification.
At pH = pKa, [A⁻] = [HA] (the ratio is 1, and log(1) = 0). This is where the buffer has maximum capacity — equal ability to neutralize added acid or base.
Buffer capacity (β) measures resistance to pH change. It equals the moles of strong acid or base needed to change pH by one unit per liter. It depends on total buffer concentration and how close pH is to pKa.
Yes, use pKb of the base equivalently, or use the conjugate acid's pKa with pH = pKa + log([B]/[BH⁺]). For NH₃/NH₄⁺ buffer: pKa(NH₄⁺) = 9.25.
Typically pKa ± 1 (where [A⁻]/[HA] is between 0.1 and 10). Outside this range, the buffer has insufficient capacity in one direction.
Choose a weak acid whose pKa is close to your target pH. The buffer is most effective when the desired pH equals the pKa. Adjust the [A⁻]/[HA] ratio for fine-tuning.