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
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
Frequently Asked Questions
How accurate are the results?
The pH Titration Buffer applies a standard formula to your inputs — accuracy depends on how precisely you measure those inputs. For planning and estimation, results are reliable. For high-stakes or professional decisions, cross-check the output with a domain expert or primary source.
What if my reagents aren't 100% pure?
Account for purity in your mass calculation: actual mass needed = theoretical mass / (purity fraction). For example, 95% pure NaCl: if you need 10g of pure NaCl, weigh out 10/0.95 = 10.53g. Always check the Certificate of Analysis for the actual purity of each lot.
How should I interpret the pH Titration Buffer output?
The result is a calculated estimate based on the formula and your inputs. Compare it against the reference values or benchmarks shown on this page to understand whether your result is high, low, or typical. For decisions with real consequences, use the output as one data point alongside direct measurement and professional advice.
When should I use a different approach?
Use this calculator for quick, formula-based estimates. If your situation involves multiple interacting variables, time-varying inputs, or safety-critical decisions, consider a dedicated software tool, professional consultation, or direct measurement. Calculators are most reliable within their stated assumptions — check that your scenario matches those assumptions before relying on the output.