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pH standard buffers (25 °C)

pH values of the NIST/IUPAC primary standards at 25 °C. Every pH-meter calibration traces back to these solutions; the everyday technical buffers 4.01, 7.00 and 10.01 are made against them.

9 rows
0.05 mol/kg potassium tetroxalate1.679
Potassium hydrogen tartrate (saturated at 25 °C)3.557
0.05 mol/kg potassium dihydrogen citrate3.776
0.05 mol/kg potassium hydrogen phthalate4.005
KH₂PO₄ + Na₂HPO₄ (0.025 mol/kg each)6.865
0.008695 mol/kg KH₂PO₄ + 0.03043 mol/kg Na₂HPO₄7.413
0.01 mol/kg borax9.180
NaHCO₃ + Na₂CO₃ (0.025 mol/kg each)10.012
Calcium hydroxide (saturated at 25 °C)12.454

Concentrations are molalities (mol/kg). Buffer pH changes with temperature (borax is about 9.46 at 0 °C), so calibrate with the value for the actual temperature or use temperature compensation.

Sources

  1. R. P. Buck et al., “Measurement of pH. Definition, standards, and procedures (IUPAC Recommendations 2002)”, Pure Appl. Chem. 74, 2169–2200 (2002).
  2. R. G. Bates, Determination of pH, 2nd ed. (Wiley, 1973); D. C. Harris, Quantitative Chemical Analysis, 9th ed. (2016), Ch. 15 (pH standards).

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