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    Standard Buffer Solutions

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    For the purpose of calibrating pH meters such as the hydrogen-calomel and the glass-calomel type, it is necessary to have on hand a number of buffer solutions of certified pH value covering the ranges of temperature and pH over which it is desired to work. Of the large number of compounds both organic and inorganic known to the chemist, comparatively few, however, have the requisite properties, such as uniformity and reproducibility of composition, freedom from deliquescence or efflorescence, ease of preparation and purification, and good buffer capacity, which would make them acceptable as buffer materials. In the past thirty years the concept of the term pH underwent a change from that of the simple definition of pH=logCH+ to the more modern definition of pH=logaH+.............(1) when it was realized that the potential of the hydrogen electrode was a measure of the activity of the hydrogen ion rather than of its concentration. Paradoxically, however, the activity of single ions cannot be determined from experiment without the use of some simplifying assumptions; it is therefore impossible to establish a pH scale on a rigorous thermodynamic basis. This point will be discussed later. The problem of purification of salts is one primarily of analytical chemistry, and the materials can be tested to determine their relative purity and reproducibility by any self-consistent method.

    Author Information:

    Manov, George G.
    Chemist, National Bureau of Standards, Washington, D. C.,

    Committee/Subcommittee: E01.02

    DOI: 10.1520/STP47876S