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 Ka-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.