Potentiometric Measurements of the Hydrogen Ion Concentrations at Constant Ionic Strength

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  • 一定イオン強度における水素イオン濃度の電位差測定

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The calibration of a glass-reference electrode pair with liquid-junction was examined for measurements of the hydrogen ion concentrations (10-2-10-7moldm-3) at high ionic strengths. The relation between pH-values (pH) based on the pH scale standardized with pHstandards and hydrogen ion concentrations (h) is expressed by the relationship pHm=M⋅ph+C where ph= log h. The M-value is related to liquid-junction potentials between the salt bridge and two pH-standards. The M-value of 1.008+0.002 was obtained for the three buffer systems (strong acid, acetic acid, and dihydrogenphosphate) at ionic strengths 0. moldm-3 (KCI, NaC1, and KNO3). The C-value, which is dependent on the ionic st rength and on the kind of the supporting electrolyte, is a function of the activity coefficient rpf, the hydrogen ion (yH) and of the liquid-junction potential between the salt bridge and the sample (Es). The values of log yH4-(δE/S), where S is the response slope of the glass electrode, calculated from the values of M. and C for hydrochloric acid, were consistent with those of our previous impel-0 regarding the liquid-junction potentials within ±0.01 pH unit. The C-value of weak acids is directly influenced by an uncertainty in the dissociation constant used. The calibration line proposed previously, pHm=ph + A, is an approximate relationship which can be derived from IiHm=-M. ph+C. A decrease in the pH-value of a strong acid accompanied by addition of a neutral salt can be explained by a decrease in the C-value with increasing ionic strength.

Journal

  • NIPPON KAGAKU KAISHI

    NIPPON KAGAKU KAISHI 1989 (12), 2028-2034, 1989-12-10

    The Chemical Society of Japan

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