Historical remarks on the Henderson-Hasselbalch equation: its advantages and limitations and a novel approach for exact pH calculation in buffer region

The theoretical titration curve of a weak acid with a strong base was considered. The limitation of the Henderson-Hasselbalch equation for the calculation of pH in the buffer region was discussed. One novel simple equation for the exact calculation of pH from the beginning of titration up to the equivalence point was derived. By using this equation with one implicit approximation (the dissociation of water), the calculation of pH values after each addition of titrant is possible. A novel equation provides the simple and exact calculation of pH in the range of buffer, and that can be done in a simple and logical way without complex hand ling of acid-base equilibrium with computer and spreadsheet software. The calculated titration curves for different concentrations of acetic acid and sodium hydroxide were shown.