Defines pH scale in terms of single reference value standard solution of potassium hydrogen phthalate and the (theoretical) slope factor

This Part of BS 1647 specifies requirements for a pH scale in terms of a single reference value standard aqueous solution of potassium hydrogen phthalate with a molality of 0.05 mol/kg, and the (theoretical) slope factor. This pH scale is appropriate for pH measurements of aqueous solutions at temperatures in the range 0 °C to 95 °C using, for calibration, the operational standard solutions specified in Part 2 of this standard.

NOTE 1 Practical pH measurements are based on one or more of the operational reference standard solutions according to circumstances and the reference value standard solution is included in the list of operational standard reference solutions from which the choice is to be made.

NOTE 2 The procedures described in Appendix B are suitable for all pH measurements, including those where other solvents and suspended matter are present, but where the electrode system is calibrated against reference materials in aqueous solution. A.4 gives information about scales for non-aqueous and mixed aqueous solvents.

The best repeatability generally obtainable is ± 0.003 but may be considerably worse than this in solutions containing reactive materials and suspended matter, especially at the extremes of the pH range 0 to 14 and at temperatures above 60 °C.

Guidance on interpretation of pH measurements is given in Appendix A and guidance on accuracy of pH measurements is given in Appendix B.

NOTE 3 The titles of the publications referred to in this Part of this standard are listed on the inside back cover.