Comments on the Concept of Buffers

Purpose: The study focused on examining the approximations employed in deriving the Henderson–Hasselbalch equation by introducing both weak bases (wb’s) and strong bases (sb’s) into solutions containing weak acids (denoted as bH’s), performed on a mass-by-mass basis. Contemporary theories were adapted to accommodate these mass-based measurements, allowing for the prediction of pH-values without the need for adjustments to K_a-values concerning temperature or activity coefficients. Methods: The experiments were performed using a standard top-pan balance with a readability of 10 mg, and pH-values were determined potentiometrically with the pH electrode positioned at the base of the beaker. For the measurements, there was no need for volumetric glassware. The top-pan balance was reset between mass and pH readings. Results: The experimental results closely matched the theoretical predictions for the systems of ethanoic acid-sodium ethanoate (HAc–NaAc), ammonium chloride-ammonia (NH₄Cl–NH₃), and sodium hydrogen carbonate-disodium carbonate (NaHCO₃–Na₂CO₃). However, there was a notable difference for the sodium hydrogen sulphate-disodium sulphate (NaHSO₄–Na₂SO₄) system, which was attributed to the limitations of the pH-electrode's performance. A similar pattern was noticed in systems where NaOH took the place of weaker bases, except in the NaHCO₃–NaOH system, where discrepancies were also seen. Conclusion: Though slight discrepancies were noted when creating buffers with NaOH, they might be attributed to the overall uncertainty of the electrode and potential temperature influences. The measurement uncertainty was assessed in further detail for HAc–NaAc and HAc–NaOH. A significantly greater uncertainty was identified for the HAc–NaOH, due to both temperature variations and differences in the impurity levels in pellets of solid NaOH.