About the pH Titration Buffer Calculator - Henderson-Hasselbalch Planning
Henderson-Hasselbalch Equation:
pH = pKa + log([A⁻] / [HA])
Calculates buffer pH from conjugate base to weak acid ratio
How the calculator solves it: instead of applying Henderson-Hasselbalch only, it solves the full charge balance for a weak monoprotic acid titrated with a strong base (25°C, Kw = 1e-14) using the Total Volume to get concentrations. That keeps the pH correct with no base added, at the equivalence point (pH above 7), and past it, where excess strong base sets the pH.
Acid-base chemistry underpins biological systems, industrial processes, and analytical chemistry. pH is the most common metric — a logarithmic scale where each unit represents a 10× change in hydrogen ion concentration.
Key relationships
- pH = −log[H⁺]; pOH = −log[OH⁻]; pH + pOH = 14 at 25°C
- Henderson-Hasselbalch equation: pH = pKa + log([A⁻]/[HA]) — calculates buffer pH from the ratio of conjugate base to weak acid
- Titration equivalence point: where moles of acid = moles of base. For strong acid + strong base, equivalence point pH = 7. For weak acid + strong base, it's above 7.
Buffer design
Buffers work best within ±1 pH unit of the pKa of the weak acid used. Outside this range, the buffer capacity drops sharply. For a target pH of 7.4 (blood), phosphate (pKa 7.2) or HEPES (pKa 7.5) are commonly chosen.
Common mistakes
- Forgetting that pH is logarithmic: going from pH 7 to pH 5 is a 100× increase in [H⁺], not a 2-unit increase
- Using strong acid concentrations before equilibrium is established — strong acids fully dissociate, weak acids only partially